[PATCH 0/7] line-log: range-scope stat, check, and -G under -L

[PATCH 0/7] line-log: range-scope stat, check, and -G under -L

[Michael Montalbo via GitGitGadget]

This series extends git log -L so that more of its diff output and commit
selection honor the tracked line ranges: the diff stat formats and --check
are supported with range-scoped results, and the -G pickaxe is scoped to the
tracked range.

It builds on top of the mm/line-log-cleanup topic [1], which integrated -L
with the standard log output pipeline and taught it the non-patch formats
--raw, --name-only, --name-status, and --summary.

With these patches the following also honor the tracked range:

 * --stat, --numstat, --shortstat: counts cover only the lines inside the
   tracked range, not the whole file.

 * --check: whitespace errors are reported only for added lines inside the
   tracked range, with the correct file line numbers.

 * -G: a commit is selected only when the pattern appears on an
   added/removed line inside the tracked range, rather than anywhere in the
   file.

The --dirstat format is deliberately rejected. Its default mode reports each
directory's share of the total churn as a percentage, computed from
whole-file byte damage (via diffcore_count_changes(), outside the line-based
pipeline that -L scopes), so bare --dirstat cannot honor the tracked range.
The --dirstat=lines mode could: it aggregates the same per-file line counts
as --numstat, which -L already scopes. But supporting only that sub-mode
while bare --dirstat still errors is a confusing split, so the whole format
is left to a follow-up; --numstat already gives the exact range-scoped
per-file counts.

-S is left matching the whole file. Unlike -G, it counts needle occurrences
per blob rather than grepping the diff, so scoping it to a range needs a
different approach; that is left to a follow-up. Patch 7, which scopes -G,
also updates the -L documentation to note the -S/-G distinction, so the
whole-file behavior of -S is not mistaken for the range-scoped behavior
around it.

Patches 1-3 are independent of the new formats: they fix two bugs in the
existing -L patch output (a leaked deletion and an off-by-one hunk header),
bring its hunk headers in line with git diff's format, and clarify the
line-range filter mm/line-log-cleanup added, whose names obscured its model
(cryptic lno_ cursors conflating the pre/post-image and 0/1-based axes, a
flat hunk-state struct, and a one-letter state pointer (s)). The two bugs
may be a hint that the model could use clarification, so patch 1 renames and
groups the filter state and patch 2 documents the model, before the fixes
that read against it. Patches 4-7 then build the new formats on top:

 * Patch 1: rename and group the filter for clarity. Spell the cryptic names
   out to the file's own forms: the line-number cursors to
   lno_in_preimage/lno_in_postimage (as in struct emit_callback) and the
   range index to idx_in_postimage, while the hunk geometry stays old/new
   (the xdiff_emit_hunk_fn convention) and moves into a sub-struct. Name the
   filter pointer (filter) and rename the struct to line_range_filter and
   the flush helper to flush_range_hunk. No behavior change.

 * Patch 2: simplify the filter by classifying removals as they arrive,
   dropping the pending_rm buffer and a latent flush_range_hunk() bug that
   leaked deletions just past the range. Make the buffered lines the hunk's
   single source of truth: flush_range_hunk() derives the counts from them
   rather than tracking them per line, dropping three more fields. Document
   the model with a block comment and worked example, and add
   begin_range_hunk() as the counterpart to flush_range_hunk(). (This
   simplification was submitted by itself previously [2] but did not
   advance, so it is re-included here.)

 * Patch 3: stop hand-rolling the synthetic hunk header and emit it through
   xdiff's own formatter via a new xdiff_emit_hunk_header() helper. The
   hand-rolled code put a count-0 side's begin one too high (the convention
   is the line before the change); routing through xdl_emit_hunk_hdr() fixes
   that by construction and, as a side effect, makes -L headers match git
   diff exactly, including its omission of a count of 1. Regenerate the two
   affected fixtures.

 * Patch 4: extract a line_range_filter_diff() helper that folds the
   filter's two preconditions into one place: inflate ctxlen to the largest
   range span so every change within a range lands in a single xdiff hunk,
   and clear XDL_EMIT_NO_HUNK_HDR so the hunk headers the filter reads are
   always emitted (its position tracking relies on both). It then runs an
   initialized filter through xdiff, flushes the final range hunk, and
   releases it; use it in builtin_diff(). The stat, check, and -G patches
   that reuse it inherit both.

 * Patch 5: reuse the filter in builtin_diffstat() for the stat formats,
   extend the -L output-format allowlist, and reject --dirstat.

 * Patch 6: reuse the filter in builtin_checkdiff() and extend the allowlist
   for --check. The separate blank-at-eof pass scans the whole file, so
   scope its report to the tracked ranges too.

 * Patch 7: scope -G to the tracked range. Expose the filter as
   diff_emit_line_ranges() and grep only the tracked range's lines,
   threading the filepair's line_ranges through the pickaxe callback. -S is
   left whole-file, and the -L documentation is updated to note that -G is
   range-scoped while -S still matches the whole file.

[1]
https://lore.kernel.org/git/pull.2094.v3.git.1780001267.gitgitgadget@gmail.com/
[2]
https://lore.kernel.org/git/pull.2099.git.1777230630020.gitgitgadget@gmail.com/

Michael Montalbo (7):
  diff: rename and group the line-range filter for clarity
  diff: simplify the line-range filter by classifying removals
    immediately
  diff: emit -L hunk headers via xdiff's formatter
  diff: extract a line-range diff helper for reuse
  line-log: support diff stat formats with -L
  diff: support --check with -L line ranges
  diffcore-pickaxe: scope -G to the -L tracked range

 Documentation/line-range-options.adoc    |  17 +-
 diff.c                                   | 491 ++++++++++++++---------
 diffcore-pickaxe.c                       |  37 +-
 revision.c                               |   6 +-
 t/t4211-line-log.sh                      | 439 +++++++++++++++++++-
 t/t4211/sha1/expect.no-assertion-error   |   2 +-
 t/t4211/sha1/expect.vanishes-early       |   6 +-
 t/t4211/sha256/expect.no-assertion-error |   2 +-
 t/t4211/sha256/expect.vanishes-early     |   6 +-
 xdiff-interface.c                        |  19 +
 xdiff-interface.h                        |  28 ++
 11 files changed, 826 insertions(+), 227 deletions(-)


base-commit: ea97ad8d017de0c9037451a78008a0fd60abea0c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2152%2Fmmontalbo%2Fmm%2Fline-log-stat-formats-followup-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2152/mmontalbo/mm/line-log-stat-formats-followup-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/2152
-- 
gitgitgadget

[PATCH 1/7] diff: rename and group the line-range filter for clarity

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

The line-range filter that mm/line-log-cleanup added uses names that
obscure its model.  The cursors lno_post/lno_pre and the index lno_0
share an lno_ prefix but conflate the pre/post-image axis with the
0-based/1-based axis, the hunk state is a flat set of rhunk_* fields,
and the filter-state pointer is just s.

The filter bridges two layers of diff.c, and its fields already used
each layer's vocabulary, but in cryptic abbreviations.  Spell them out
to the form the rest of the file uses, so that the patches that follow
can simplify and fix it with those clearer names in place:

  - lno_post/lno_pre -> lno_in_postimage/lno_in_preimage, the
    line-number cursors, matching the counters in struct emit_callback
  - lno_0 -> idx_in_postimage, the 0-based range index
  - the hunk-header geometry stays old/new (old_begin, new_begin, and
    counts) to match the xdiff_emit_hunk_fn callback and the
    "@@ -<old> +<new> @@" header it feeds, but moves from flat rhunk_*
    fields into a "hunk" sub-struct, so accesses read
    filter->hunk.old_begin
  - flush_rhunk -> flush_range_hunk
  - the filter-state pointer in each callback: s -> filter

Also rename the struct line_range_callback to line_range_filter: it is
a filter over xdiff output, not merely a callback.

No behavior change.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c | 192 +++++++++++++++++++++++++++++----------------------------
 1 file changed, 97 insertions(+), 95 deletions(-)

diff --git a/diff.c b/diff.c
index 5a584fa1d5..1e043c959f 100644
--- a/diff.c
+++ b/diff.c
@@ -623,15 +623,15 @@ struct emit_callback {
  * reveals whether they precede an in-range line (flush into range hunk) or
  * an out-of-range line (discard).
  */
-struct line_range_callback {
+struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
 	void *orig_cb_data;
 	const struct range_set *ranges;	/* 0-based [start, end) */
 	unsigned int cur_range;		/* index into the range_set */
 
 	/* Post/pre-image line counters (1-based, set from hunk headers) */
-	long lno_post;
-	long lno_pre;
+	long lno_in_postimage;
+	long lno_in_preimage;
 
 	/*
 	 * Function name from most recent xdiff hunk header;
@@ -640,12 +640,14 @@ struct line_range_callback {
 	char func[80];
 	long funclen;
 
-	/* Range hunk being accumulated for the current range */
-	struct strbuf rhunk;
-	long rhunk_old_begin, rhunk_old_count;
-	long rhunk_new_begin, rhunk_new_count;
-	int rhunk_active;
-	int rhunk_has_changes;		/* any '+' or '-' lines? */
+	/* The range hunk being accumulated for the current range. */
+	struct {
+		struct strbuf lines;	/* buffered in-range diff lines */
+		long old_begin, old_count;
+		long new_begin, new_count;
+		int active;
+		int has_changes;	/* any '+' or '-' line? */
+	} hunk;
 
 	/* Removal lines not yet known to be in-range */
 	struct strbuf pending_rm;
@@ -2540,26 +2542,26 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
-static void discard_pending_rm(struct line_range_callback *s)
+static void discard_pending_rm(struct line_range_filter *filter)
 {
-	strbuf_reset(&s->pending_rm);
-	s->pending_rm_count = 0;
+	strbuf_reset(&filter->pending_rm);
+	filter->pending_rm_count = 0;
 }
 
-static void flush_rhunk(struct line_range_callback *s)
+static void flush_range_hunk(struct line_range_filter *filter)
 {
 	struct strbuf hdr = STRBUF_INIT;
 	const char *p, *end;
 
-	if (!s->rhunk_active || s->ret)
+	if (!filter->hunk.active || filter->ret)
 		return;
 
 	/* Drain any pending removal lines into the range hunk */
-	if (s->pending_rm_count) {
-		strbuf_addbuf(&s->rhunk, &s->pending_rm);
-		s->rhunk_old_count += s->pending_rm_count;
-		s->rhunk_has_changes = 1;
-		discard_pending_rm(s);
+	if (filter->pending_rm_count) {
+		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
+		filter->hunk.old_count += filter->pending_rm_count;
+		filter->hunk.has_changes = 1;
+		discard_pending_rm(filter);
 	}
 
 	/*
@@ -2568,22 +2570,22 @@ static void flush_rhunk(struct line_range_callback *s)
 	 * ctxlen causes xdiff to emit context covering a range that
 	 * has no changes in this commit.
 	 */
-	if (!s->rhunk_has_changes) {
-		s->rhunk_active = 0;
-		strbuf_reset(&s->rhunk);
+	if (!filter->hunk.has_changes) {
+		filter->hunk.active = 0;
+		strbuf_reset(&filter->hunk.lines);
 		return;
 	}
 
 	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    s->rhunk_old_begin, s->rhunk_old_count,
-		    s->rhunk_new_begin, s->rhunk_new_count);
-	if (s->funclen > 0) {
+		    filter->hunk.old_begin, filter->hunk.old_count,
+		    filter->hunk.new_begin, filter->hunk.new_count);
+	if (filter->funclen > 0) {
 		strbuf_addch(&hdr, ' ');
-		strbuf_add(&hdr, s->func, s->funclen);
+		strbuf_add(&hdr, filter->func, filter->funclen);
 	}
 	strbuf_addch(&hdr, '\n');
 
-	s->ret = s->orig_line_fn(s->orig_cb_data, hdr.buf, hdr.len);
+	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
 
 	/*
@@ -2591,18 +2593,18 @@ static void flush_rhunk(struct line_range_callback *s)
 	 * The cast discards const because xdiff_emit_line_fn takes
 	 * char *, though fn_out_consume does not modify the buffer.
 	 */
-	p = s->rhunk.buf;
-	end = p + s->rhunk.len;
-	while (!s->ret && p < end) {
+	p = filter->hunk.lines.buf;
+	end = p + filter->hunk.lines.len;
+	while (!filter->ret && p < end) {
 		const char *eol = memchr(p, '\n', end - p);
 		unsigned long line_len = eol ? (unsigned long)(eol - p + 1)
 					     : (unsigned long)(end - p);
-		s->ret = s->orig_line_fn(s->orig_cb_data, (char *)p, line_len);
+		filter->ret = filter->orig_line_fn(filter->orig_cb_data, (char *)p, line_len);
 		p += line_len;
 	}
 
-	s->rhunk_active = 0;
-	strbuf_reset(&s->rhunk);
+	filter->hunk.active = 0;
+	strbuf_reset(&filter->hunk.lines);
 }
 
 static void line_range_hunk_fn(void *data,
@@ -2610,7 +2612,7 @@ static void line_range_hunk_fn(void *data,
 			       long new_begin, long new_nr UNUSED,
 			       const char *func, long funclen)
 {
-	struct line_range_callback *s = data;
+	struct line_range_filter *filter = data;
 
 	/*
 	 * When count > 0, begin is 1-based.  When count == 0, begin is
@@ -2622,104 +2624,104 @@ static void line_range_hunk_fn(void *data,
 	 * flush or discard them when the next content line reveals
 	 * whether the removals precede in-range content.
 	 */
-	s->lno_post = new_begin;
-	s->lno_pre = old_begin;
+	filter->lno_in_postimage = new_begin;
+	filter->lno_in_preimage = old_begin;
 
 	if (funclen > 0) {
-		if (funclen > (long)sizeof(s->func))
-			funclen = sizeof(s->func);
-		memcpy(s->func, func, funclen);
+		if (funclen > (long)sizeof(filter->func))
+			funclen = sizeof(filter->func);
+		memcpy(filter->func, func, funclen);
 	}
-	s->funclen = funclen;
+	filter->funclen = funclen;
 }
 
 static int line_range_line_fn(void *priv, char *line, unsigned long len)
 {
-	struct line_range_callback *s = priv;
+	struct line_range_filter *filter = priv;
 	const struct range *cur;
-	long lno_0, cur_pre;
+	long idx_in_postimage, cur_pre;
 
-	if (s->ret)
-		return s->ret;
+	if (filter->ret)
+		return filter->ret;
 
 	if (line[0] == '-') {
-		if (!s->pending_rm_count)
-			s->pending_rm_pre_begin = s->lno_pre;
-		s->lno_pre++;
-		strbuf_add(&s->pending_rm, line, len);
-		s->pending_rm_count++;
-		return s->ret;
+		if (!filter->pending_rm_count)
+			filter->pending_rm_pre_begin = filter->lno_in_preimage;
+		filter->lno_in_preimage++;
+		strbuf_add(&filter->pending_rm, line, len);
+		filter->pending_rm_count++;
+		return filter->ret;
 	}
 
 	if (line[0] == '\\') {
-		if (s->pending_rm_count)
-			strbuf_add(&s->pending_rm, line, len);
-		else if (s->rhunk_active)
-			strbuf_add(&s->rhunk, line, len);
+		if (filter->pending_rm_count)
+			strbuf_add(&filter->pending_rm, line, len);
+		else if (filter->hunk.active)
+			strbuf_add(&filter->hunk.lines, line, len);
 		/* otherwise outside tracked range; drop silently */
-		return s->ret;
+		return filter->ret;
 	}
 
 	if (line[0] != '+' && line[0] != ' ')
 		BUG("unexpected diff line type '%c'", line[0]);
 
-	lno_0 = s->lno_post - 1;
-	cur_pre = s->lno_pre;	/* save before advancing for context lines */
-	s->lno_post++;
+	idx_in_postimage = filter->lno_in_postimage - 1;
+	cur_pre = filter->lno_in_preimage;	/* save before advancing for context lines */
+	filter->lno_in_postimage++;
 	if (line[0] == ' ')
-		s->lno_pre++;
+		filter->lno_in_preimage++;
 
 	/* Advance past ranges we've passed */
-	while (s->cur_range < s->ranges->nr &&
-	       lno_0 >= s->ranges->ranges[s->cur_range].end) {
-		if (s->rhunk_active)
-			flush_rhunk(s);
-		discard_pending_rm(s);
-		s->cur_range++;
+	while (filter->cur_range < filter->ranges->nr &&
+	       idx_in_postimage >= filter->ranges->ranges[filter->cur_range].end) {
+		if (filter->hunk.active)
+			flush_range_hunk(filter);
+		discard_pending_rm(filter);
+		filter->cur_range++;
 	}
 
 	/* Past all ranges */
-	if (s->cur_range >= s->ranges->nr) {
-		discard_pending_rm(s);
-		return s->ret;
+	if (filter->cur_range >= filter->ranges->nr) {
+		discard_pending_rm(filter);
+		return filter->ret;
 	}
 
-	cur = &s->ranges->ranges[s->cur_range];
+	cur = &filter->ranges->ranges[filter->cur_range];
 
 	/* Before current range */
-	if (lno_0 < cur->start) {
-		discard_pending_rm(s);
-		return s->ret;
+	if (idx_in_postimage < cur->start) {
+		discard_pending_rm(filter);
+		return filter->ret;
 	}
 
 	/* In range so start a new range hunk if needed */
-	if (!s->rhunk_active) {
-		s->rhunk_active = 1;
-		s->rhunk_has_changes = 0;
-		s->rhunk_new_begin = lno_0 + 1;
-		s->rhunk_old_begin = s->pending_rm_count
-			? s->pending_rm_pre_begin : cur_pre;
-		s->rhunk_old_count = 0;
-		s->rhunk_new_count = 0;
-		strbuf_reset(&s->rhunk);
+	if (!filter->hunk.active) {
+		filter->hunk.active = 1;
+		filter->hunk.has_changes = 0;
+		filter->hunk.new_begin = idx_in_postimage + 1;
+		filter->hunk.old_begin = filter->pending_rm_count
+			? filter->pending_rm_pre_begin : cur_pre;
+		filter->hunk.old_count = 0;
+		filter->hunk.new_count = 0;
+		strbuf_reset(&filter->hunk.lines);
 	}
 
 	/* Flush pending removals into range hunk */
-	if (s->pending_rm_count) {
-		strbuf_addbuf(&s->rhunk, &s->pending_rm);
-		s->rhunk_old_count += s->pending_rm_count;
-		s->rhunk_has_changes = 1;
-		discard_pending_rm(s);
+	if (filter->pending_rm_count) {
+		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
+		filter->hunk.old_count += filter->pending_rm_count;
+		filter->hunk.has_changes = 1;
+		discard_pending_rm(filter);
 	}
 
-	strbuf_add(&s->rhunk, line, len);
-	s->rhunk_new_count++;
+	strbuf_add(&filter->hunk.lines, line, len);
+	filter->hunk.new_count++;
 	if (line[0] == '+')
-		s->rhunk_has_changes = 1;
+		filter->hunk.has_changes = 1;
 	else
-		s->rhunk_old_count++;
+		filter->hunk.old_count++;
 
-	return s->ret;
+	return filter->ret;
 }
 
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
@@ -4086,7 +4088,7 @@ static void builtin_diff(const char *name_a,
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
 		} else if (line_ranges) {
-			struct line_range_callback lr_state;
+			struct line_range_filter lr_state;
 			unsigned int i;
 			long max_span = 0;
 
@@ -4094,7 +4096,7 @@ static void builtin_diff(const char *name_a,
 			lr_state.orig_line_fn = fn_out_consume;
 			lr_state.orig_cb_data = &ecbdata;
 			lr_state.ranges = line_ranges;
-			strbuf_init(&lr_state.rhunk, 0);
+			strbuf_init(&lr_state.hunk.lines, 0);
 			strbuf_init(&lr_state.pending_rm, 0);
 
 			/*
@@ -4125,11 +4127,11 @@ static void builtin_diff(const char *name_a,
 				die("unable to generate diff for %s",
 				    one->path);
 
-			flush_rhunk(&lr_state);
+			flush_range_hunk(&lr_state);
 			if (lr_state.ret)
 				die("unable to generate diff for %s",
 				    one->path);
-			strbuf_release(&lr_state.rhunk);
+			strbuf_release(&lr_state.hunk.lines);
 			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
-- 
gitgitgadget

[PATCH 2/7] diff: simplify the line-range filter by classifying removals immediately

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

The filter buffered '-' lines in a pending_rm strbuf, deferring their
classification until a '+' or ' ' line revealed the post-image
position.  That buffering is unnecessary: a removal occupies no
post-image line, so it does not advance lno_in_postimage, and xdiff
emits removals before additions within a change.  A '-' therefore
arrives while lno_in_postimage already holds the index the following
'+'/' ' will occupy, and can be classified against the ranges as it
arrives.

The buffering also hid a bug: flush_range_hunk() drained pending_rm into
the range hunk whenever the hunk was active, even after lno_in_postimage
had advanced past the tracked range, so a deletion just after the
tracked function leaked into the patch.  Classifying each line as it
arrives removes the pending_rm buffer, the discard_pending_rm() helper,
three struct fields, and makes that bug impossible by construction.

With every line classified on arrival, the buffered lines are the
hunk's single source of truth, so the old/new counts need not be kept
alongside them: flush_range_hunk() derives the counts (and whether the
hunk holds any change) from the buffer when it builds the header.  Drop
the per-line counting and the old_count, new_count, and has_changes
fields; there is no longer a second tally that could fall out of sync
with the buffer.

Add begin_range_hunk() to open the accumulator at the first in-range
line, seeding both begins from the live image cursors, as the
counterpart to flush_range_hunk().  With the counting gone too,
line_range_line_fn() now only appends an in-range line.

Document the coordinate model: a block comment on struct
line_range_filter states it (the pre/post-image cursors, the 0-based
idx_in_postimage, removals classified by the following line) with a
worked example.

Add tests for the leaked trailing deletion this fixes, the symmetric
leading-deletion case, and the filter's range boundaries (a change at
the first and last line of a range, and a pure in-range deletion).

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c              | 215 ++++++++++++++++++++++++--------------------
 t/t4211-line-log.sh | 125 ++++++++++++++++++++++++++
 2 files changed, 243 insertions(+), 97 deletions(-)

diff --git a/diff.c b/diff.c
index 1e043c959f..ee765d7ac2 100644
--- a/diff.c
+++ b/diff.c
@@ -610,18 +610,58 @@ struct emit_callback {
 };
 
 /*
- * State for the line-range callback wrappers that sit between
- * xdi_diff_outf() and fn_out_consume().  xdiff produces a normal,
- * unfiltered diff; the wrappers intercept each hunk header and line,
- * track post-image position, and forward only lines that fall within
- * the requested ranges.  Contiguous in-range lines are collected into
- * range hunks and flushed with a synthetic @@ header so that
- * fn_out_consume() sees well-formed unified-diff fragments.
+ * Line-range filter: scopes "git log -L" output to the tracked ranges.
  *
- * Removal lines ('-') cannot be classified by post-image position, so
- * they are buffered in pending_rm until the next '+' or ' ' line
- * reveals whether they precede an in-range line (flush into range hunk) or
- * an out-of-range line (discard).
+ * It sits between xdi_diff_outf() and an output callback (fn_out_consume,
+ * diffstat_consume, checkdiff_consume).  xdiff produces a normal diff; the
+ * filter forwards only the lines inside the requested ranges, collecting
+ * contiguous in-range lines into a "range hunk" emitted with a synthetic
+ * @@ header so the callback sees well-formed unified-diff fragments.
+ *
+ * A diff describes the change from a pre-image to a post-image.  Each
+ * line is context (' ', in both), a removal ('-', pre-image only), or
+ * an addition ('+', post-image only).  -L tracks ranges in the
+ * post-image, so a line is in range by its post-image position.
+ *
+ * Two 1-based cursors track the next line in each image, named as in
+ * struct emit_callback and seeded from the xdiff hunk header:
+ *
+ *	lno_in_postimage  advances on '+' and ' '   (lines in the post-image)
+ *	lno_in_preimage   advances on '-' and ' '   (lines in the pre-image)
+ *
+ * Ranges are 0-based half-open [start, end), so a line is tested at the
+ * 0-based index idx_in_postimage = lno_in_postimage - 1.
+ *
+ * A '-' is not present in the post-image, so it has no post-image line
+ * number of its own.  Since it does not advance lno_in_postimage, it is
+ * classified at the idx_in_postimage that the following '+'/' ' will
+ * occupy.  xdiff emits a change's removals before its additions, so that
+ * index is already known when the '-' arrives.
+ *
+ * The synthetic "@@ -<old> +<new> @@" header has two sides, old (the
+ * pre-image) and new (the post-image), matching the xdiff_emit_hunk_fn
+ * callback; the hunk.old_begin / hunk.new_begin fields below hold those
+ * begins, and flush_range_hunk() derives the counts from the buffered
+ * lines.
+ *
+ * Example, tracking post-image line 2 (range [1, 2)) of:
+ *
+ *	pre-image  post-image
+ *	1 a        1 a
+ *	2 b        2 X      (b -> X)
+ *	3 c        3 c
+ *
+ *	classify each line by idx_in_postimage.  The pre and post columns
+ *	are each cursor's value while that line is classified, i.e. before
+ *	the line advances them (pre = lno_in_preimage,
+ *	post = lno_in_postimage, idx = idx_in_postimage):
+ *	' a'  pre 1  post 1  idx 0  ->  before start, skip
+ *	'-b'  pre 2  post 2  idx 1  ->  keep (removal)
+ *	'+X'  pre 3  post 2  idx 1  ->  keep (addition)
+ *	' c'  pre 3  post 3  idx 2  ->  past end, flush
+ *
+ * -b and +X share idx = 1 because -b did not advance lno_in_postimage;
+ * both land in the range hunk, flushed when ' c' crosses the range end.
  */
 struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
@@ -640,20 +680,18 @@ struct line_range_filter {
 	char func[80];
 	long funclen;
 
-	/* The range hunk being accumulated for the current range. */
+	/*
+	 * The range hunk being accumulated.  At most one is live at a time:
+	 * it is flushed and reset as the cursor leaves each range (and once
+	 * more at end of diff), then reused for the next range.
+	 */
 	struct {
 		struct strbuf lines;	/* buffered in-range diff lines */
-		long old_begin, old_count;
-		long new_begin, new_count;
+		long old_begin;
+		long new_begin;
 		int active;
-		int has_changes;	/* any '+' or '-' line? */
 	} hunk;
 
-	/* Removal lines not yet known to be in-range */
-	struct strbuf pending_rm;
-	int pending_rm_count;
-	long pending_rm_pre_begin;	/* pre-image line of first pending */
-
 	int ret;			/* latched error from orig_line_fn */
 };
 
@@ -2542,26 +2580,48 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
-static void discard_pending_rm(struct line_range_filter *filter)
+/*
+ * Begin a range hunk at the first in-range line.  Its position fixes the
+ * hunk's begins, taken from the two image cursors before they advance:
+ * new_begin from the post-image, old_begin from the pre-image.  The line
+ * counts are not tracked here; flush_range_hunk() derives them from the
+ * buffered lines.
+ */
+static void begin_range_hunk(struct line_range_filter *filter)
 {
-	strbuf_reset(&filter->pending_rm);
-	filter->pending_rm_count = 0;
+	filter->hunk.active = 1;
+	filter->hunk.new_begin = filter->lno_in_postimage;
+	filter->hunk.old_begin = filter->lno_in_preimage;
+	strbuf_reset(&filter->hunk.lines);
 }
 
 static void flush_range_hunk(struct line_range_filter *filter)
 {
 	struct strbuf hdr = STRBUF_INIT;
 	const char *p, *end;
+	long old_count = 0, new_count = 0;
+	int has_changes = 0;
 
 	if (!filter->hunk.active || filter->ret)
 		return;
 
-	/* Drain any pending removal lines into the range hunk */
-	if (filter->pending_rm_count) {
-		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
-		filter->hunk.old_count += filter->pending_rm_count;
-		filter->hunk.has_changes = 1;
-		discard_pending_rm(filter);
+	/*
+	 * Derive the hunk's geometry from the buffered lines: a ' '
+	 * counts on both sides, a '-' on the old side, a '+' on the new.
+	 * A '-' or '+' marks a real change; the "\ No newline at end of
+	 * file" marker (line[0] == '\\') counts on neither side.
+	 */
+	p = filter->hunk.lines.buf;
+	end = p + filter->hunk.lines.len;
+	while (p < end) {
+		const char *eol = memchr(p, '\n', end - p);
+		if (*p == ' ' || *p == '-')
+			old_count++;
+		if (*p == ' ' || *p == '+')
+			new_count++;
+		if (*p == '-' || *p == '+')
+			has_changes = 1;
+		p = eol ? eol + 1 : end;
 	}
 
 	/*
@@ -2570,15 +2630,15 @@ static void flush_range_hunk(struct line_range_filter *filter)
 	 * ctxlen causes xdiff to emit context covering a range that
 	 * has no changes in this commit.
 	 */
-	if (!filter->hunk.has_changes) {
+	if (!has_changes) {
 		filter->hunk.active = 0;
 		strbuf_reset(&filter->hunk.lines);
 		return;
 	}
 
 	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    filter->hunk.old_begin, filter->hunk.old_count,
-		    filter->hunk.new_begin, filter->hunk.new_count);
+		    filter->hunk.old_begin, old_count,
+		    filter->hunk.new_begin, new_count);
 	if (filter->funclen > 0) {
 		strbuf_addch(&hdr, ' ');
 		strbuf_add(&hdr, filter->func, filter->funclen);
@@ -2618,11 +2678,6 @@ static void line_range_hunk_fn(void *data,
 	 * When count > 0, begin is 1-based.  When count == 0, begin is
 	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
 	 * that type will arrive, so the value is unused.
-	 *
-	 * Any pending removal lines from the previous xdiff hunk are
-	 * intentionally left in pending_rm: the line callback will
-	 * flush or discard them when the next content line reveals
-	 * whether the removals precede in-range content.
 	 */
 	filter->lno_in_postimage = new_begin;
 	filter->lno_in_preimage = old_begin;
@@ -2638,88 +2693,56 @@ static void line_range_hunk_fn(void *data,
 static int line_range_line_fn(void *priv, char *line, unsigned long len)
 {
 	struct line_range_filter *filter = priv;
-	const struct range *cur;
-	long idx_in_postimage, cur_pre;
+	long idx_in_postimage;
+	int in_range;
 
 	if (filter->ret)
 		return filter->ret;
 
-	if (line[0] == '-') {
-		if (!filter->pending_rm_count)
-			filter->pending_rm_pre_begin = filter->lno_in_preimage;
-		filter->lno_in_preimage++;
-		strbuf_add(&filter->pending_rm, line, len);
-		filter->pending_rm_count++;
-		return filter->ret;
-	}
-
 	if (line[0] == '\\') {
-		if (filter->pending_rm_count)
-			strbuf_add(&filter->pending_rm, line, len);
-		else if (filter->hunk.active)
+		if (filter->hunk.active)
 			strbuf_add(&filter->hunk.lines, line, len);
-		/* otherwise outside tracked range; drop silently */
 		return filter->ret;
 	}
 
-	if (line[0] != '+' && line[0] != ' ')
+	if (line[0] != '+' && line[0] != ' ' && line[0] != '-')
 		BUG("unexpected diff line type '%c'", line[0]);
 
+	/*
+	 * idx_in_postimage is this line's 0-based post-image index (see the model on
+	 * struct line_range_filter).  The cursors are advanced only after
+	 * the line is classified, so a '-' is tested at the same idx_in_postimage as
+	 * the '+'/' ' that follows it.
+	 */
 	idx_in_postimage = filter->lno_in_postimage - 1;
-	cur_pre = filter->lno_in_preimage;	/* save before advancing for context lines */
-	filter->lno_in_postimage++;
-	if (line[0] == ' ')
-		filter->lno_in_preimage++;
 
-	/* Advance past ranges we've passed */
+	/* Retire ranges we have passed, flushing the one we leave. */
 	while (filter->cur_range < filter->ranges->nr &&
 	       idx_in_postimage >= filter->ranges->ranges[filter->cur_range].end) {
 		if (filter->hunk.active)
 			flush_range_hunk(filter);
-		discard_pending_rm(filter);
 		filter->cur_range++;
 	}
 
-	/* Past all ranges */
-	if (filter->cur_range >= filter->ranges->nr) {
-		discard_pending_rm(filter);
-		return filter->ret;
-	}
+	in_range = filter->cur_range < filter->ranges->nr &&
+		   idx_in_postimage >= filter->ranges->ranges[filter->cur_range].start &&
+		   idx_in_postimage < filter->ranges->ranges[filter->cur_range].end;
 
-	cur = &filter->ranges->ranges[filter->cur_range];
+	if (in_range) {
+		if (!filter->hunk.active)
+			begin_range_hunk(filter);
 
-	/* Before current range */
-	if (idx_in_postimage < cur->start) {
-		discard_pending_rm(filter);
-		return filter->ret;
+		strbuf_add(&filter->hunk.lines, line, len);
 	}
 
-	/* In range so start a new range hunk if needed */
-	if (!filter->hunk.active) {
-		filter->hunk.active = 1;
-		filter->hunk.has_changes = 0;
-		filter->hunk.new_begin = idx_in_postimage + 1;
-		filter->hunk.old_begin = filter->pending_rm_count
-			? filter->pending_rm_pre_begin : cur_pre;
-		filter->hunk.old_count = 0;
-		filter->hunk.new_count = 0;
-		strbuf_reset(&filter->hunk.lines);
-	}
-
-	/* Flush pending removals into range hunk */
-	if (filter->pending_rm_count) {
-		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
-		filter->hunk.old_count += filter->pending_rm_count;
-		filter->hunk.has_changes = 1;
-		discard_pending_rm(filter);
-	}
-
-	strbuf_add(&filter->hunk.lines, line, len);
-	filter->hunk.new_count++;
-	if (line[0] == '+')
-		filter->hunk.has_changes = 1;
-	else
-		filter->hunk.old_count++;
+	/*
+	 * Advance each image's cursor: a line present in that image (see
+	 * the model) consumes one of its line numbers.
+	 */
+	if (line[0] != '-')
+		filter->lno_in_postimage++;
+	if (line[0] != '+')
+		filter->lno_in_preimage++;
 
 	return filter->ret;
 }
@@ -4097,7 +4120,6 @@ static void builtin_diff(const char *name_a,
 			lr_state.orig_cb_data = &ecbdata;
 			lr_state.ranges = line_ranges;
 			strbuf_init(&lr_state.hunk.lines, 0);
-			strbuf_init(&lr_state.pending_rm, 0);
 
 			/*
 			 * Inflate ctxlen so that all changes within
@@ -4132,7 +4154,6 @@ static void builtin_diff(const char *name_a,
 				die("unable to generate diff for %s",
 				    one->path);
 			strbuf_release(&lr_state.hunk.lines);
-			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index ca4eb7bbc7..e9691066de 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -738,6 +738,131 @@ test_expect_success '-L with -G filters to diff-text matches' '
 	grep "F2 + 2" actual
 '
 
+test_expect_success 'setup for trailing deletion test' '
+	git checkout --orphan trailing-del &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 1;
+	}
+	// trailing comment
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "add file with trailing comment" &&
+	# Modify tracked() AND delete the trailing comment in
+	# one commit, so the commit touches the tracked range
+	# and is not filtered out by the revision walker.
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 2;
+	}
+	EOF
+	git commit -a -m "modify tracked and delete trailing comment"
+'
+
+test_expect_success '-L does not include deletions past end of tracked range' '
+	git log -L:tracked:file.c --format= -1 -p >actual &&
+	# The trailing comment deletion is outside the tracked
+	# range and should not appear in the patch output.
+	test_grep "return 2" actual &&
+	test_grep ! "trailing comment" actual
+'
+
+test_expect_success '-L includes leading deletions resolved by in-range line' '
+	git checkout --orphan leading-del &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	// leading comment
+	void tracked()
+	{
+	    return 1;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "add file with leading comment" &&
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 2;
+	}
+	EOF
+	git commit -a -m "modify tracked and delete leading comment" &&
+	git log -L:tracked:file.c --format= -1 -p >actual &&
+	# The leading comment deletion is resolved by the next
+	# non-removal line (void tracked), which is in range: a
+	# removal is classified by the position of the following
+	# line, so it joins the range that line falls in.
+	test_grep "return 2" actual &&
+	test_grep "leading comment" actual
+'
+
+test_expect_success 'setup for line-range filter edge cases' '
+	git checkout --orphan filter-edge &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	void before()
+	{
+	    return 0;
+	}
+
+	void tracked()
+	{
+	    int a = 1;
+	    int b = 2;
+	    int c = 3;
+	    return a + b + c;
+	}
+
+	void after()
+	{
+	    return 9;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "initial"
+'
+
+test_expect_success '-L change at exact first line of range' '
+	git checkout filter-edge &&
+	# Change the function signature (first line of range)
+	sed "s/void tracked/int tracked/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "change first line" &&
+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
+	test_grep "change first line" actual &&
+	test_grep "+int tracked" actual &&
+	test_grep "\\-void tracked" actual
+'
+
+test_expect_success '-L change at exact last line of range' '
+	git checkout filter-edge &&
+	git reset --hard HEAD~1 &&
+	# Change the closing brace line (last line of range)
+	sed "s/^}$/} \/\/ end tracked/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "change last line" &&
+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
+	test_grep "change last line" actual &&
+	test_grep "end tracked" actual
+'
+
+test_expect_success '-L pure deletion in range (no additions)' '
+	git checkout filter-edge &&
+	git reset --hard HEAD~1 &&
+	# Delete a line inside tracked() without adding anything
+	sed "/int c/d" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "pure deletion" &&
+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
+	test_grep "pure deletion" actual &&
+	test_grep "\\-.*int c" actual
+'
+
 test_expect_success '-L with --diff-filter=M excludes root commit' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c --diff-filter=M --format=%s --no-patch >actual &&
-- 
gitgitgadget

[PATCH 3/7] diff: emit -L hunk headers via xdiff's formatter

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

The line-range filter builds its own "@@ -<old> +<new> @@" header for
each range hunk.  For a side with no lines (count 0, such as the old
side of a pure insertion), the begin should be the number of the line
before the change, per the convention git diff and xdl_emit_hunk_hdr()
follow.  The hand-rolled code's begin was one too high; in t4211 this
produced

	@@ -25,0 +18,9 @@

an old begin of 25 in a 24-line file, where git diff would give 24.

Stop hand-rolling the header.  flush_range_hunk() now formats it through
xdiff's own emitter: a new xdiff_emit_hunk_header() helper wraps
xdl_emit_hunk_hdr(), the function that produces every other diff's hunk
headers.  The count-0 begin is then correct by construction, and as a
side effect -L headers match git diff exactly, including its omission of
a count of 1 ("@@ -22 +22 @@" rather than "@@ -22,1 +22,1 @@").

xdiff's hunk callback already hands line_range_hunk_fn() a count-0 begin
decremented, so undo that when seeding the cursors and let the formatter
re-apply the convention once, at emit time.

The off-by-one predates this series, and the two regenerated fixtures
reach it from different origins: no-assertion-error has carried it since
its test was added in ab60c693a2 (line-log: fix assertion error,
2025-08-18), while vanishes-early acquired it when 86e986f166 (line-log:
route -L output through the standard diff pipeline) reshaped its tracked
line into a pure insertion.  vanishes-early also drops its count-1
counts.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c                                   | 27 +++++++++++-------------
 t/t4211/sha1/expect.no-assertion-error   |  2 +-
 t/t4211/sha1/expect.vanishes-early       |  6 +++---
 t/t4211/sha256/expect.no-assertion-error |  2 +-
 t/t4211/sha256/expect.vanishes-early     |  6 +++---
 xdiff-interface.c                        | 19 +++++++++++++++++
 xdiff-interface.h                        | 15 +++++++++++++
 7 files changed, 54 insertions(+), 23 deletions(-)

diff --git a/diff.c b/diff.c
index ee765d7ac2..9751bb6798 100644
--- a/diff.c
+++ b/diff.c
@@ -2636,14 +2636,9 @@ static void flush_range_hunk(struct line_range_filter *filter)
 		return;
 	}
 
-	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    filter->hunk.old_begin, old_count,
-		    filter->hunk.new_begin, new_count);
-	if (filter->funclen > 0) {
-		strbuf_addch(&hdr, ' ');
-		strbuf_add(&hdr, filter->func, filter->funclen);
-	}
-	strbuf_addch(&hdr, '\n');
+	xdiff_emit_hunk_header(&hdr, filter->hunk.old_begin, old_count,
+			       filter->hunk.new_begin, new_count,
+			       filter->func, filter->funclen);
 
 	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
@@ -2668,19 +2663,21 @@ static void flush_range_hunk(struct line_range_filter *filter)
 }
 
 static void line_range_hunk_fn(void *data,
-			       long old_begin, long old_nr UNUSED,
-			       long new_begin, long new_nr UNUSED,
+			       long old_begin, long old_nr,
+			       long new_begin, long new_nr,
 			       const char *func, long funclen)
 {
 	struct line_range_filter *filter = data;
 
 	/*
-	 * When count > 0, begin is 1-based.  When count == 0, begin is
-	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
-	 * that type will arrive, so the value is unused.
+	 * Seed the per-image line cursors from the hunk header's begins.  For
+	 * a side with no lines (count 0), xdiff's callback has already moved
+	 * its begin to the line before the change, so add one back to recover
+	 * the true 1-based start.  xdiff_emit_hunk_header() reapplies that -1
+	 * when the clipped hunk is emitted.
 	 */
-	filter->lno_in_postimage = new_begin;
-	filter->lno_in_preimage = old_begin;
+	filter->lno_in_postimage = new_nr ? new_begin : new_begin + 1;
+	filter->lno_in_preimage = old_nr ? old_begin : old_begin + 1;
 
 	if (funclen > 0) {
 		if (funclen > (long)sizeof(filter->func))
diff --git a/t/t4211/sha1/expect.no-assertion-error b/t/t4211/sha1/expect.no-assertion-error
index 54c568f273..95faf51a7b 100644
--- a/t/t4211/sha1/expect.no-assertion-error
+++ b/t/t4211/sha1/expect.no-assertion-error
@@ -8,7 +8,7 @@ diff --git a/b.c b/b.c
 index bf79c2f..27c829c 100644
 --- a/b.c
 +++ b/b.c
-@@ -25,0 +18,9 @@
+@@ -24,0 +18,9 @@
 +long f(long x)
 +{
 +	int s = 0;
diff --git a/t/t4211/sha1/expect.vanishes-early b/t/t4211/sha1/expect.vanishes-early
index a413ad3659..e4b1a201d5 100644
--- a/t/t4211/sha1/expect.vanishes-early
+++ b/t/t4211/sha1/expect.vanishes-early
@@ -8,7 +8,7 @@ diff --git a/a.c b/a.c
 index 0b9cae5..5de3ea4 100644
 --- a/a.c
 +++ b/a.c
-@@ -23,0 +24,1 @@ int main ()
+@@ -22,0 +24 @@ int main ()
 +/* incomplete lines are bad! */
 
 commit 100b61a6f2f720f812620a9d10afb3a960ccb73c
@@ -21,7 +21,7 @@ diff --git a/a.c b/a.c
 index 5e709a1..0b9cae5 100644
 --- a/a.c
 +++ b/a.c
-@@ -22,1 +22,1 @@ int main ()
+@@ -22 +22 @@ int main ()
 -}
 +}
 \ No newline at end of file
@@ -37,5 +37,5 @@ new file mode 100644
 index 0000000..444e415
 --- /dev/null
 +++ b/a.c
-@@ -0,0 +20,1 @@
+@@ -0,0 +20 @@
 +}
diff --git a/t/t4211/sha256/expect.no-assertion-error b/t/t4211/sha256/expect.no-assertion-error
index c25f2ce19c..815d27f7f1 100644
--- a/t/t4211/sha256/expect.no-assertion-error
+++ b/t/t4211/sha256/expect.no-assertion-error
@@ -8,7 +8,7 @@ diff --git a/b.c b/b.c
 index 69cb69c..a0d566e 100644
 --- a/b.c
 +++ b/b.c
-@@ -25,0 +18,9 @@
+@@ -24,0 +18,9 @@
 +long f(long x)
 +{
 +	int s = 0;
diff --git a/t/t4211/sha256/expect.vanishes-early b/t/t4211/sha256/expect.vanishes-early
index bc33b963dc..263fc9eaac 100644
--- a/t/t4211/sha256/expect.vanishes-early
+++ b/t/t4211/sha256/expect.vanishes-early
@@ -8,7 +8,7 @@ diff --git a/a.c b/a.c
 index e4fa1d8..62c1fc2 100644
 --- a/a.c
 +++ b/a.c
-@@ -23,0 +24,1 @@ int main ()
+@@ -22,0 +24 @@ int main ()
 +/* incomplete lines are bad! */
 
 commit 29f32ac3141c48b22803e5c4127b719917b67d0f8ca8c5248bebfa2a19f7da10
@@ -21,7 +21,7 @@ diff --git a/a.c b/a.c
 index d325124..e4fa1d8 100644
 --- a/a.c
 +++ b/a.c
-@@ -22,1 +22,1 @@ int main ()
+@@ -22 +22 @@ int main ()
 -}
 +}
 \ No newline at end of file
@@ -37,5 +37,5 @@ new file mode 100644
 index 0000000..9f550c3
 --- /dev/null
 +++ b/a.c
-@@ -0,0 +20,1 @@
+@@ -0,0 +20 @@
 +}
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 5ee2b96d0a..32e04630ee 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -91,6 +91,25 @@ static int xdiff_outf(void *priv_, mmbuffer_t *mb, int nbuf)
 	return 0;
 }
 
+static int strbuf_out_line(void *priv, mmbuffer_t *mb, int nbuf)
+{
+	struct strbuf *out = priv;
+	int i;
+	for (i = 0; i < nbuf; i++)
+		strbuf_add(out, mb[i].ptr, mb[i].size);
+	return 0;
+}
+
+void xdiff_emit_hunk_header(struct strbuf *out,
+			    long old_begin, long old_count,
+			    long new_begin, long new_count,
+			    const char *func, long funclen)
+{
+	xdemitcb_t ecb = { .priv = out, .out_line = strbuf_out_line };
+	xdl_emit_hunk_hdr(old_begin, old_count, new_begin, new_count,
+			  func, funclen, &ecb);
+}
+
 /*
  * Trim down common substring at the end of the buffers,
  * but end on a complete line.
diff --git a/xdiff-interface.h b/xdiff-interface.h
index ce54e1c0e0..51c88296ed 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -76,4 +76,19 @@ int xdiff_compare_lines(const char *l1, long s1,
  */
 unsigned long xdiff_hash_string(const char *s, size_t len, long flags);
 
+struct strbuf;
+
+/*
+ * Append a unified-diff hunk header to `out`, e.g.
+ * "@@ -<old> +<new> @@ func\n".  The header comes from wrapping xdiff's
+ * own hunk-header emitter, so it matches what a normal diff would
+ * produce for these begins and counts.  For a side with no lines
+ * (count 0) the begin is the line before the change, and a count of 1
+ * is omitted.
+ */
+void xdiff_emit_hunk_header(struct strbuf *out,
+			    long old_begin, long old_count,
+			    long new_begin, long new_count,
+			    const char *func, long funclen);
+
 #endif
-- 
gitgitgadget

[PATCH 4/7] diff: extract a line-range diff helper for reuse

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

builtin_diff() open-codes the line-range filter setup and teardown
around its xdi_diff_outf() call: zero the struct, point it at the
output callback, inflate ctxlen to the largest range span so each range
yields a single xdiff hunk, run the diff, flush the trailing range
hunk, and release the buffer.  The upcoming -L stat and check formats
need the same sequence.

Extract line_range_filter_init() for the setup and a
line_range_filter_diff() helper that prepares the xdiff config the
filter needs, runs an initialized filter through xdi_diff_outf(),
flushes the final range hunk, and releases it, returning the latched
error.  The helper inflates ctxlen to the largest range span so each
range yields a single xdiff hunk, and clears XDL_EMIT_NO_HUNK_HDR so
the hunk headers the filter seeds its position from are always emitted.
Folding both into the helper keeps these invariants, which the filter's
position tracking relies on, in a single place for every consumer.
builtin_diff() now does init + line_range_filter_diff(); the next two
patches reuse them in builtin_diffstat() and builtin_checkdiff()
instead of repeating the boilerplate.

No behavior change: builtin_diff() leaves XDL_EMIT_NO_HUNK_HDR unset,
so clearing it is a no-op until the suppressing consumers arrive.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c | 100 +++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 61 insertions(+), 39 deletions(-)

diff --git a/diff.c b/diff.c
index 9751bb6798..6233a96bf0 100644
--- a/diff.c
+++ b/diff.c
@@ -2580,6 +2580,18 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
+static void line_range_filter_init(struct line_range_filter *filter,
+				   const struct range_set *ranges,
+				   xdiff_emit_line_fn line_fn,
+				   void *cb_data)
+{
+	memset(filter, 0, sizeof(*filter));
+	filter->orig_line_fn = line_fn;
+	filter->orig_cb_data = cb_data;
+	filter->ranges = ranges;
+	strbuf_init(&filter->hunk.lines, 0);
+}
+
 /*
  * Begin a range hunk at the first in-range line.  Its position fixes the
  * hunk's begins, taken from the two image cursors before they advance:
@@ -2744,6 +2756,50 @@ static int line_range_line_fn(void *priv, char *line, unsigned long len)
 	return filter->ret;
 }
 
+/*
+ * Run an xdiff pass through an initialized line-range filter, flush the
+ * final range hunk, and release the filter.  Inflates ctxlen to the largest
+ * range span first, so that every change within a single range lands in one
+ * xdiff hunk and the inter-change context is emitted; the filter then clips
+ * back to range boundaries.  The optimal ctxlen depends on where changes fall
+ * within the range, which is only known after xdiff runs, so the max span is
+ * the upper bound that guarantees correctness in a single pass.  Every
+ * consumer (patch, diffstat, check) relies on one xdiff hunk per range, so
+ * this lives here rather than at each call site.  Also clears
+ * XDL_EMIT_NO_HUNK_HDR: the filter seeds its per-image position from the hunk
+ * headers, so a consumer that otherwise suppresses them (diffstat) still gets
+ * them here.  Returns non-zero if xdiff or any forwarded callback failed.
+ */
+static int line_range_filter_diff(struct line_range_filter *filter,
+				  mmfile_t *mf1, mmfile_t *mf2,
+				  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	const struct range_set *ranges = filter->ranges;
+	long max_span = 0;
+	unsigned int i;
+	int ret;
+
+	for (i = 0; i < ranges->nr; i++) {
+		long span = ranges->ranges[i].end - ranges->ranges[i].start;
+		if (span > max_span)
+			max_span = span;
+	}
+	if (max_span > xecfg->ctxlen)
+		xecfg->ctxlen = max_span;
+
+	/* the filter seeds its per-image position from hunk headers */
+	xecfg->flags &= ~XDL_EMIT_NO_HUNK_HDR;
+
+	ret = xdi_diff_outf(mf1, mf2, line_range_hunk_fn,
+			    line_range_line_fn, filter, xpp, xecfg);
+	if (!ret) {
+		flush_range_hunk(filter);
+		ret = filter->ret;
+	}
+	strbuf_release(&filter->hunk.lines);
+	return ret;
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
@@ -4108,49 +4164,15 @@ static void builtin_diff(const char *name_a,
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
 		} else if (line_ranges) {
-			struct line_range_filter lr_state;
-			unsigned int i;
-			long max_span = 0;
+			struct line_range_filter lr_filter;
 
-			memset(&lr_state, 0, sizeof(lr_state));
-			lr_state.orig_line_fn = fn_out_consume;
-			lr_state.orig_cb_data = &ecbdata;
-			lr_state.ranges = line_ranges;
-			strbuf_init(&lr_state.hunk.lines, 0);
-
-			/*
-			 * Inflate ctxlen so that all changes within
-			 * any single range are merged into one xdiff
-			 * hunk and the inter-change context is emitted.
-			 * The callback clips back to range boundaries.
-			 *
-			 * The optimal ctxlen depends on where changes
-			 * fall within the range, which is only known
-			 * after xdiff runs; the max range span is the
-			 * upper bound that guarantees correctness in a
-			 * single pass.
-			 */
-			for (i = 0; i < line_ranges->nr; i++) {
-				long span = line_ranges->ranges[i].end -
-					    line_ranges->ranges[i].start;
-				if (span > max_span)
-					max_span = span;
-			}
-			if (max_span > xecfg.ctxlen)
-				xecfg.ctxlen = max_span;
-
-			if (xdi_diff_outf(&mf1, &mf2,
-					  line_range_hunk_fn,
-					  line_range_line_fn,
-					  &lr_state, &xpp, &xecfg))
-				die("unable to generate diff for %s",
-				    one->path);
+			line_range_filter_init(&lr_filter, line_ranges,
+					       fn_out_consume, &ecbdata);
 
-			flush_range_hunk(&lr_state);
-			if (lr_state.ret)
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
 				die("unable to generate diff for %s",
 				    one->path);
-			strbuf_release(&lr_state.hunk.lines);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
-- 
gitgitgadget

[PATCH 5/7] line-log: support diff stat formats with -L

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Reuse the line_range_filter in builtin_diffstat() to produce
range-scoped statistics.  When a filepair carries line_ranges, the
filter wraps diffstat_consume() as its output callback, forwarding only
in-range lines for counting.  flush_range_hunk() replays buffered
content through diffstat_consume(), which ignores synthetic @@ headers
since it only counts '+' and '-' lines.

Expand the output format allowlist in setup_revisions() to accept
--stat, --numstat, and --shortstat with -L.

Leave --dirstat out of the allowlist so it is rejected like any other
unsupported format.  Its default mode counts each file's whole-file
byte damage via diffcore_count_changes(), outside the line-based
pipeline that the -L filter scopes, so bare --dirstat cannot honor the
tracked range.  The --dirstat=lines mode could: it aggregates the same
per-file line counts as --numstat, which -L already scopes.  But
accepting only that sub-mode while bare --dirstat keeps erroring is a
confusing split, so the whole format is deferred to a follow-up;
--numstat already reports the exact range-scoped per-file counts.

Also drop "yet" from the generic -L rejection message ("does not
yet support the requested diff format").  Some rejected formats do
not fit a line range at all, so "yet" wrongly implied they are all
just awaiting support.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  12 ++-
 diff.c                                |  13 ++-
 revision.c                            |   6 +-
 t/t4211-line-log.sh                   | 150 ++++++++++++++++++++++----
 4 files changed, 155 insertions(+), 26 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index 72f639b5e7..1a25f55bb1 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -9,10 +9,14 @@
 	_<start>_ and _<end>_ (or _<funcname>_) must exist in the starting revision.
 	You can specify this option more than once. Implies `--patch`.
 	Patch output can be suppressed using `--no-patch`.
-	Non-patch diff formats `--raw`, `--name-only`, `--name-status`,
-	and `--summary` are supported.  Diff stat formats
-	(`--stat`, `--numstat`, `--shortstat`, `--dirstat`) are not
-	currently implemented.
+	The following non-patch diff formats are supported: `--raw`,
+	`--name-only`, `--name-status`, `--summary`,
+	`--stat`, `--numstat`, and `--shortstat`.
+	The stat formats show range-scoped counts: only lines within
+	the tracked range are counted.  `--dirstat` is not supported
+	with `-L`: it summarizes change as each directory's share of
+	the total churn, not as counts for the tracked lines.  Use
+	`--numstat` for exact per-file counts within the range.
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
diff --git a/diff.c b/diff.c
index 6233a96bf0..026fafeb90 100644
--- a/diff.c
+++ b/diff.c
@@ -4289,7 +4289,18 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 		xecfg.ctxlen = o->context;
 		xecfg.interhunkctxlen = o->interhunkcontext;
 		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
-		if (xdi_diff_outf(&mf1, &mf2, NULL,
+
+		if (p->line_ranges) {
+			struct line_range_filter lr_filter;
+
+			line_range_filter_init(&lr_filter, p->line_ranges,
+					       diffstat_consume, diffstat);
+
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
+				die("unable to generate diffstat for %s",
+				    one->path);
+		} else if (xdi_diff_outf(&mf1, &mf2, NULL,
 				  diffstat_consume, diffstat, &xpp, &xecfg))
 			die("unable to generate diffstat for %s", one->path);
 
diff --git a/revision.c b/revision.c
index 6a8101e8b7..2c76e15778 100644
--- a/revision.c
+++ b/revision.c
@@ -3193,8 +3193,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 	     (revs->diffopt.output_format &
 	      ~(DIFF_FORMAT_PATCH | DIFF_FORMAT_NO_OUTPUT |
 		DIFF_FORMAT_RAW | DIFF_FORMAT_NAME |
-		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY))))
-		die(_("-L does not yet support the requested diff format"));
+		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY |
+		DIFF_FORMAT_NUMSTAT | DIFF_FORMAT_DIFFSTAT |
+		DIFF_FORMAT_SHORTSTAT))))
+		die(_("-L does not support the requested diff format"));
 
 	if (revs->expand_tabs_in_log < 0)
 		revs->expand_tabs_in_log = revs->expand_tabs_in_log_default;
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index e9691066de..af37bd532f 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -176,24 +176,15 @@ test_expect_success '--name-status shows status and path' '
 	test_grep ! "^@@" actual
 '
 
-test_expect_success '--stat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --stat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--numstat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --numstat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--shortstat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --shortstat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--dirstat is not yet supported with -L' '
+test_expect_success '--dirstat is not supported with -L' '
+	# --dirstat is not supported with -L: its default mode measures
+	# whole-file change, not the tracked lines, and the
+	# --dirstat=lines variant is deferred too, so both forms are
+	# rejected like any other unsupported format.
 	test_must_fail git log -L1,24:b.c --dirstat 2>err &&
-	test_grep "does not yet support" err
+	test_grep "does not support" err &&
+	test_must_fail git log -L1,24:b.c --dirstat=lines 2>err &&
+	test_grep "does not support" err
 '
 
 test_expect_success 'setup for checking fancy rename following' '
@@ -887,9 +878,9 @@ test_expect_success '-L with -S suppresses non-matching commits' '
 	test_cmp expect actual
 '
 
-test_expect_success '--full-diff is not yet supported with -L' '
+test_expect_success '--full-diff is not supported with -L' '
 	test_must_fail git log -L1,24:b.c --full-diff 2>err &&
-	test_grep "does not yet support" err
+	test_grep "does not support" err
 '
 
 test_expect_success '-L --oneline has no extra blank line before diff' '
@@ -900,6 +891,127 @@ test_expect_success '-L --oneline has no extra blank line before diff' '
 	test_grep "^diff --git" line2
 '
 
+test_expect_success 'setup for stat range-scoping tests' '
+	git checkout --orphan stat-scoping &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "Add func1() and func2()" &&
+
+	# Modify both functions in a single commit so that
+	# whole-file stats differ from range-scoped stats.
+	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "Modify both functions"
+'
+
+test_expect_success '--numstat counts only lines in tracked range' '
+	# "Modify both functions" changes one line in func1 and one in
+	# func2.  Whole-file numstat would show 2 added, 2 deleted.
+	# Range-scoped numstat for func2 should show only 1 and 1.
+	git log -L:func2:file.c --numstat --format=%s -1 >actual &&
+	test_grep "Modify both functions" actual &&
+	test_grep "^1	1	file.c$" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--numstat counts only additions for root commit' '
+	# Root commit creates both func1 (4 lines) and func2 (4 lines).
+	# Whole-file numstat would show 9 lines added.  Range-scoped
+	# numstat for func2 should show only 4.
+	git log -L:func2:file.c --numstat --format=%s >actual &&
+	test_grep "Add func1() and func2()" actual &&
+	test_grep "^4	0	file.c$" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--stat counts only lines in tracked range' '
+	git log -L:func2:file.c --stat --format=%s -1 >actual &&
+	test_grep "Modify both functions" actual &&
+	test_grep "file.c |" actual &&
+	test_grep "1 insertion" actual &&
+	test_grep "1 deletion" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--shortstat counts only lines in tracked range' '
+	# --shortstat prints only the summary line: no per-file "file.c |"
+	# line.  Counts are range-scoped as for --numstat above.
+	git log -L:func2:file.c --shortstat --format=%s -1 >actual &&
+	test_grep "Modify both functions" actual &&
+	test_grep "1 insertion" actual &&
+	test_grep "1 deletion" actual &&
+	test_grep ! "file.c |" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--numstat across renames and multiple commits' '
+	# parallel-change carries the tracked function f across an a.c -> b.c
+	# rename and a merge of two parallel histories.  With -M, --numstat
+	# follows the rename and reports range-scoped (not whole-file)
+	# added/removed counts for f per commit; the file column flips from
+	# b.c to a.c at the rename as the walk goes back in time.  Commits
+	# that do not change the range of f emit no row (the merge and the
+	# pure file-move produce nothing), so there are fewer rows than
+	# commits.
+	git checkout parallel-change &&
+	git log -M -L ":f:b.c" --format= --numstat >actual &&
+	cat >expect <<-\EOF &&
+	1	1	b.c
+	1	1	a.c
+	1	1	a.c
+	1	1	a.c
+	1	0	a.c
+	13	0	a.c
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '-L multiple ranges with --numstat excludes untracked change' '
+	git checkout --orphan multi-range &&
+	git reset --hard &&
+	cat >m.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+
+	int func3()
+	{
+	    return F3;
+	}
+	EOF
+	git add m.c &&
+	test_tick &&
+	git commit -m "add m.c" &&
+	# Change all three functions but track only func1 and func2.
+	# Whole-file numstat would be 3 3; a 2 2 result proves the
+	# untracked func3 change is excluded and the two ranges just sum.
+	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" -e "s/F3/F3 + 3/" m.c >tmp &&
+	mv tmp m.c &&
+	git commit -a -m "Modify all three functions" &&
+	git log -L:func1:m.c -L:func2:m.c --numstat --format=%s -1 >actual &&
+	test_grep "Modify all three functions" actual &&
+	test_grep "^2	2	m.c$" actual &&
+	test_grep ! "^3	3	m.c$" actual
+'
+
 test_expect_success '--summary shows new file on root commit' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c --summary --format= >actual &&
-- 
gitgitgadget

[PATCH 6/7] diff: support --check with -L line ranges

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

builtin_checkdiff() runs its own xdiff pass to detect whitespace
errors in newly added lines.  When -L is active, the check should
be scoped to the tracked line ranges rather than the whole file.

Reuse the line_range_filter to wrap checkdiff_consume(), the same
pattern already used for patch output and diffstat.  The filter
forwards only in-range lines for whitespace checking.

checkdiff reports the file line number of each error, which it
normally learns from the hunk header via checkdiff_consume_hunk().
The filter synthesizes its own hunk headers, so give it an optional
hunk callback and route checkdiff_consume_hunk() through it; this
sets the post-image position before the in-range lines are replayed.
Without it the reported line numbers would count from the start of
the range hunk rather than the start of the file.

The trailing blank-at-eof check is a second pass that scans the whole
file via check_blank_at_eof(), so gate its report on the tracked
ranges as well; otherwise a blank line added at end of file is
reported even when it lies outside the range.

Add DIFF_FORMAT_CHECKDIFF to the -L output format allowlist in
setup_revisions() so that -L --check is accepted, and list --check
among the supported formats in the documentation.  Add tests covering
that whitespace errors are reported, scoped to the tracked range, and
labeled with the correct file line number, including when two errors
in one range are separated by a gap that would otherwise split into
multiple xdiff hunks.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  2 +-
 diff.c                                | 65 ++++++++++++++++++-
 revision.c                            |  2 +-
 t/t4211-line-log.sh                   | 92 +++++++++++++++++++++++++++
 4 files changed, 156 insertions(+), 5 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index 1a25f55bb1..ec92f43ae4 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -10,7 +10,7 @@
 	You can specify this option more than once. Implies `--patch`.
 	Patch output can be suppressed using `--no-patch`.
 	The following non-patch diff formats are supported: `--raw`,
-	`--name-only`, `--name-status`, `--summary`,
+	`--name-only`, `--name-status`, `--summary`, `--check`,
 	`--stat`, `--numstat`, and `--shortstat`.
 	The stat formats show range-scoped counts: only lines within
 	the tracked range are counted.  `--dirstat` is not supported
diff --git a/diff.c b/diff.c
index 026fafeb90..519c513356 100644
--- a/diff.c
+++ b/diff.c
@@ -665,6 +665,12 @@ struct emit_callback {
  */
 struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
+	/*
+	 * Optional; consumers that report file line numbers (e.g.
+	 * checkdiff) need the synthetic hunk header to set their
+	 * post-image position before in-range lines are replayed.
+	 */
+	xdiff_emit_hunk_fn orig_hunk_fn;
 	void *orig_cb_data;
 	const struct range_set *ranges;	/* 0-based [start, end) */
 	unsigned int cur_range;		/* index into the range_set */
@@ -2652,6 +2658,17 @@ static void flush_range_hunk(struct line_range_filter *filter)
 			       filter->hunk.new_begin, new_count,
 			       filter->func, filter->funclen);
 
+	/*
+	 * Inform a line-numbering consumer of the post-image position
+	 * before replaying lines, mirroring the hunk callback xdiff
+	 * would have issued for a non-scoped diff.
+	 */
+	if (filter->orig_hunk_fn)
+		filter->orig_hunk_fn(filter->orig_cb_data,
+				filter->hunk.old_begin, old_count,
+				filter->hunk.new_begin, new_count,
+				filter->func, filter->funclen);
+
 	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
 
@@ -4330,11 +4347,29 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 	diff_free_filespec_data(two);
 }
 
+/*
+ * Is the 0-based line index within any of the tracked ranges?
+ * (range_set ranges are 0-based, half-open [start, end).)  This is a
+ * one-shot query for a single line and scans; the streaming filter
+ * (line_range_line_fn) uses a forward cursor instead.
+ */
+static int idx_in_ranges(const struct range_set *ranges, long idx)
+{
+	unsigned int i;
+
+	for (i = 0; i < ranges->nr; i++)
+		if (idx >= ranges->ranges[i].start &&
+		    idx < ranges->ranges[i].end)
+			return 1;
+	return 0;
+}
+
 static void builtin_checkdiff(const char *name_a, const char *name_b,
 			      const char *attr_path,
 			      struct diff_filespec *one,
 			      struct diff_filespec *two,
-			      struct diff_options *o)
+			      struct diff_options *o,
+			      const struct range_set *line_ranges)
 {
 	mmfile_t mf1, mf2;
 	struct checkdiff_t data;
@@ -4374,7 +4409,19 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 		memset(&xecfg, 0, sizeof(xecfg));
 		xecfg.ctxlen = 1; /* at least one context line */
 		xpp.flags = 0;
-		if (xdi_diff_outf(&mf1, &mf2, checkdiff_consume_hunk,
+
+		if (line_ranges) {
+			struct line_range_filter lr_filter;
+
+			line_range_filter_init(&lr_filter, line_ranges,
+					       checkdiff_consume, &data);
+			lr_filter.orig_hunk_fn = checkdiff_consume_hunk;
+
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
+				die("unable to generate checkdiff for %s",
+				    one->path);
+		} else if (xdi_diff_outf(&mf1, &mf2, checkdiff_consume_hunk,
 				  checkdiff_consume, &data,
 				  &xpp, &xecfg))
 			die("unable to generate checkdiff for %s", one->path);
@@ -4387,6 +4434,17 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 			check_blank_at_eof(&mf1, &mf2, &ecbdata);
 			blank_at_eof = ecbdata.blank_at_eof_in_postimage;
 
+			/*
+			 * check_blank_at_eof() scans the whole file; with -L,
+			 * keep the report only when its line is in a tracked
+			 * range.  The error's location is the first trailing
+			 * blank line (blank_at_eof, 1-based; ranges 0-based), so
+			 * we scope by that line.
+			 */
+			if (blank_at_eof && line_ranges &&
+			    !idx_in_ranges(line_ranges, blank_at_eof - 1))
+				blank_at_eof = 0;
+
 			if (blank_at_eof) {
 				static char *err;
 				if (!err)
@@ -5179,7 +5237,8 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 	diff_fill_oid_info(p->one, o->repo->index);
 	diff_fill_oid_info(p->two, o->repo->index);
 
-	builtin_checkdiff(name, other, attr_path, p->one, p->two, o);
+	builtin_checkdiff(name, other, attr_path, p->one, p->two, o,
+			  p->line_ranges);
 }
 
 void repo_diff_setup(struct repository *r, struct diff_options *options)
diff --git a/revision.c b/revision.c
index 2c76e15778..7abb287451 100644
--- a/revision.c
+++ b/revision.c
@@ -3195,7 +3195,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 		DIFF_FORMAT_RAW | DIFF_FORMAT_NAME |
 		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY |
 		DIFF_FORMAT_NUMSTAT | DIFF_FORMAT_DIFFSTAT |
-		DIFF_FORMAT_SHORTSTAT))))
+		DIFF_FORMAT_SHORTSTAT | DIFF_FORMAT_CHECKDIFF))))
 		die(_("-L does not support the requested diff format"));
 
 	if (revs->expand_tabs_in_log < 0)
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index af37bd532f..9d351aa05f 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -1018,4 +1018,96 @@ test_expect_success '--summary shows new file on root commit' '
 	test_grep "create mode 100644 file.c" actual
 '
 
+test_expect_success 'setup for --check test' '
+	git checkout --orphan check-test &&
+	git reset --hard &&
+	cat >check.c <<-\EOF &&
+	void tracked()
+	{
+	    return;
+	}
+
+	void other()
+	{
+	    return;
+	}
+	EOF
+	git add check.c &&
+	test_tick &&
+	git commit -m "add check.c" &&
+	# Introduce trailing whitespace errors in both functions
+	sed "s/return;/return; /" check.c >check.c.tmp &&
+	mv check.c.tmp check.c &&
+	git commit -a -m "introduce trailing whitespace"
+'
+
+test_expect_success '--check scoped to tracked range with correct file line' '
+	# tracked() trailing whitespace is at check.c:3; report it with the
+	# real file line number, not a count from the start of the range
+	# hunk.  other() at check.c:8 is outside the range and is excluded.
+	test_must_fail git log -L:tracked:check.c --check --format= >actual &&
+	test_grep "check.c:3: trailing whitespace" actual &&
+	test_grep ! "check.c:8:" actual
+'
+
+test_expect_success '--check reports each of several tracked ranges' '
+	# Track both functions as separate ranges.  Each range is flushed
+	# as its own hunk, so the second error must report its real file
+	# line (check.c:8), not continue the numbering from the first
+	# range (check.c:3).
+	test_must_fail git log -L:tracked:check.c -L:other:check.c \
+		--check --format= >actual &&
+	test_grep "check.c:3: trailing whitespace" actual &&
+	test_grep "check.c:8: trailing whitespace" actual
+'
+
+test_expect_success '--check line numbers stay correct across a gap in one range' '
+	git checkout --orphan check-gap &&
+	git reset --hard &&
+	cat >gap.c <<-\EOF &&
+	void tracked()
+	{
+	    int a = 1;
+	    int b = 2;
+	    int c = 3;
+	    int d = 4;
+	    int e = 5;
+	    int g = 7;
+	    return;
+	}
+	EOF
+	git add gap.c &&
+	test_tick &&
+	git commit -m "add gap.c" &&
+	# Two trailing-whitespace errors within one tracked range,
+	# separated by clean lines.  ctxlen is inflated to the range span,
+	# so they land in a single xdiff hunk with the gap as context;
+	# both must report their real file line number, with the context
+	# lines between them counted.
+	sed -e "s/int a = 1;/int a = 1; /" -e "s/int g = 7;/int g = 7; /" gap.c >tmp &&
+	mv tmp gap.c &&
+	git commit -a -m "ws errors with a gap" &&
+	test_must_fail git log -L:tracked:gap.c --check --format= >actual &&
+	test_grep "gap.c:3: trailing whitespace" actual &&
+	test_grep "gap.c:8: trailing whitespace" actual
+'
+
+test_expect_success '--check does not report blank-at-eof outside the range' '
+	git checkout --orphan check-eof &&
+	git reset --hard &&
+	printf "void tracked()\n{\n    return;\n}\n\nint tail = 1;\n" >eof.c &&
+	git add eof.c &&
+	test_tick &&
+	git commit -m "add eof.c" &&
+	# One commit introduces a trailing-whitespace error inside tracked()
+	# (line 3) and a blank line at end of file (line 7, outside the
+	# range).  The blank-at-eof check scans the whole file, so it must be
+	# scoped: report the in-range error, not the out-of-range EOF blank.
+	printf "void tracked()\n{\n    return; \n}\n\nint tail = 1;\n\n" >eof.c &&
+	git commit -a -m "ws in range, blank at eof out of range" &&
+	test_must_fail git log -L:tracked:eof.c --check --format= >actual &&
+	test_grep "eof.c:3: trailing whitespace" actual &&
+	test_grep ! "blank line at EOF" actual
+'
+
 test_done
-- 
gitgitgadget

[PATCH 7/7] diffcore-pickaxe: scope -G to the -L tracked range

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

git log -L scopes its diff output to the tracked range, but pickaxe
(-S, -G) still runs in diffcore over the whole-file change, so -L -G
selects a commit whenever the pattern appears in any added or removed
line of the file, even outside the tracked range.

Teach -G to honor the range.  diff_grep() already runs an xdiff pass
and greps the +/- lines; route that pass through the line-range filter
so only the tracked range's lines are grepped.  Expose the filter as
diff_emit_line_ranges(), a line-range-scoped xdi_diff_outf(), thread
the filepair's line_ranges through the pickaxe callback, and pass it
from pickaxe_match().  Skip scoping under textconv, whose output is not
in the original file's line coordinates.

-G needs only a hit/no-hit answer, so the line-number concerns the
filter handles for patch and check output do not apply here.

-S is left matching the whole file: it counts needle occurrences per
blob rather than grepping the diff, so scoping it needs a different
approach, left to a follow-up.  has_changes() takes the range parameter
but ignores it for now.

Document the resulting -L pickaxe scoping: -G is range-scoped, while -S
still matches the whole file.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  5 +-
 diff.c                                | 15 ++++++
 diffcore-pickaxe.c                    | 37 +++++++++++---
 t/t4211-line-log.sh                   | 72 +++++++++++++++++++++++++--
 xdiff-interface.h                     | 13 +++++
 5 files changed, 130 insertions(+), 12 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index ec92f43ae4..7cfae1499c 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -20,6 +20,9 @@
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
-as are pickaxe options (`-S`, `-G`) and `--diff-filter`.
+as are pickaxe options (`-S`, `-G`) and `--diff-filter`.  `-G` is
+scoped to the tracked range; `-S` is still evaluated over the whole
+file, so an `-S` query may select a commit for a change outside the
+range.
 +
 include::line-range-format.adoc[]
diff --git a/diff.c b/diff.c
index 519c513356..a8f346621b 100644
--- a/diff.c
+++ b/diff.c
@@ -2817,6 +2817,21 @@ static int line_range_filter_diff(struct line_range_filter *filter,
 	return ret;
 }
 
+/*
+ * Expose the in-file line-range filter to callers outside diff.c (e.g.
+ * pickaxe -G); see xdiff-interface.h for the contract.
+ */
+int diff_emit_line_ranges(mmfile_t *one, mmfile_t *two,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	struct line_range_filter filter;
+
+	line_range_filter_init(&filter, ranges, line_fn, cb_data);
+	return line_range_filter_diff(&filter, one, two, xpp, xecfg);
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index a52d569911..047b2bf7ac 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -16,7 +16,8 @@
 
 typedef int (*pickaxe_fn)(mmfile_t *one, mmfile_t *two,
 			  struct diff_options *o,
-			  regex_t *regexp, kwset_t kws);
+			  regex_t *regexp, kwset_t kws,
+			  const struct range_set *ranges);
 
 struct diffgrep_cb {
 	regex_t *regexp;
@@ -42,7 +43,8 @@ static int diffgrep_consume(void *priv, char *line, unsigned long len)
 
 static int diff_grep(mmfile_t *one, mmfile_t *two,
 		     struct diff_options *o,
-		     regex_t *regexp, kwset_t kws UNUSED)
+		     regex_t *regexp, kwset_t kws UNUSED,
+		     const struct range_set *ranges)
 {
 	struct diffgrep_cb ecbdata;
 	xpparam_t xpp;
@@ -50,8 +52,11 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	int ret;
 
 	/*
-	 * We have both sides; need to run textual diff and see if
-	 * the pattern appears on added/deleted lines.
+	 * We have both sides; need to run textual diff and see if the
+	 * pattern appears on added/deleted lines.  Under -L (ranges set),
+	 * forward only the tracked range's lines so the match is scoped.
+	 * -G needs only a hit/no-hit answer, so the line-number bookkeeping
+	 * the filter does for -L patch and check output is irrelevant here.
 	 */
 	memset(&xpp, 0, sizeof(xpp));
 	memset(&xecfg, 0, sizeof(xecfg));
@@ -65,8 +70,12 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	 * An xdiff error might be our "data->hit" from above. See the
 	 * comment for xdiff_emit_line_fn in xdiff-interface.h
 	 */
-	ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
-			    &ecbdata, &xpp, &xecfg);
+	if (ranges)
+		ret = diff_emit_line_ranges(one, two, ranges, diffgrep_consume,
+					    &ecbdata, &xpp, &xecfg);
+	else
+		ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
+				    &ecbdata, &xpp, &xecfg);
 	if (ecbdata.hit)
 		return 1;
 	if (ret)
@@ -119,8 +128,13 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws,
 
 static int has_changes(mmfile_t *one, mmfile_t *two,
 		       struct diff_options *o UNUSED,
-		       regex_t *regexp, kwset_t kws)
+		       regex_t *regexp, kwset_t kws,
+		       const struct range_set *ranges UNUSED)
 {
+	/*
+	 * -S counts needle occurrences in each whole blob.  Scoping this to
+	 * a -L range is left to a follow-up; for now -S ignores the range.
+	 */
 	unsigned int c1 = one ? contains(one, regexp, kws, 0) : 0;
 	unsigned int c2 = two ? contains(two, regexp, kws, c1 + 1) : 0;
 	return c1 != c2;
@@ -132,6 +146,7 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	struct userdiff_driver *textconv_one = NULL;
 	struct userdiff_driver *textconv_two = NULL;
 	mmfile_t mf1, mf2;
+	const struct range_set *ranges;
 	int ret;
 
 	/* ignore unmerged */
@@ -169,7 +184,13 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	mf1.size = fill_textconv(o->repo, textconv_one, p->one, &mf1.ptr);
 	mf2.size = fill_textconv(o->repo, textconv_two, p->two, &mf2.ptr);
 
-	ret = fn(&mf1, &mf2, o, regexp, kws);
+	/*
+	 * -L scopes the search to the tracked range, but the range is in
+	 * original-file line coordinates that do not map onto textconv
+	 * output, so search the whole file when textconv is in play.
+	 */
+	ranges = (textconv_one || textconv_two) ? NULL : p->line_ranges;
+	ret = fn(&mf1, &mf2, o, regexp, kws, ranges);
 
 	if (textconv_one)
 		free(mf1.ptr);
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 9d351aa05f..3d35b20178 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -722,9 +722,9 @@ test_expect_success '-L with -S filters to string-count changes' '
 test_expect_success '-L with -G filters to diff-text matches' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c -G "F2 [+] 2" --format= >actual &&
-	# -G greps the whole-file diff text, not just the tracked range;
-	# combined with -L, this selects commits that both touch func2
-	# and have "F2 + 2" in their diff.
+	# -G greps the diff text, and under -L only the lines in the
+	# tracked range (unlike -S above, which searches the whole file);
+	# this selects commits whose change to func2 contains "F2 + 2".
 	test $(grep -c "^diff --git" actual) = 1 &&
 	grep "F2 + 2" actual
 '
@@ -1110,4 +1110,70 @@ test_expect_success '--check does not report blank-at-eof outside the range' '
 	test_grep ! "blank line at EOF" actual
 '
 
+test_expect_success '-L -G is scoped to the tracked range' '
+	git checkout --orphan grep-scope &&
+	git reset --hard &&
+	cat >gp.c <<-\EOF &&
+	int func1()
+	{
+	    return ALPHA;
+	}
+
+	int func2()
+	{
+	    return BETA;
+	}
+	EOF
+	git add gp.c &&
+	test_tick &&
+	git commit -m "add gp.c" &&
+	sed -e "s/ALPHA/ALPHA2/" -e "s/BETA/BETA2/" gp.c >tmp &&
+	mv tmp gp.c &&
+	git commit -a -m "touch both functions" &&
+	# The commit changes ALPHA (func1) and BETA (func2).  Tracking func2,
+	# -G BETA matches its in-range change; -G ALPHA must not, since ALPHA
+	# changes only outside the tracked range.
+	git log -L:func2:gp.c -G BETA --format=%s >actual &&
+	test_grep "touch both functions" actual &&
+	git log -L:func2:gp.c -G ALPHA --format=%s >actual &&
+	test_grep ! "touch both functions" actual
+'
+
+test_expect_success '-L -G searches the whole file under textconv' '
+	git checkout --orphan grep-textconv &&
+	git reset --hard &&
+	cat >tc.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+	EOF
+	git add tc.c &&
+	test_tick &&
+	git commit -m "add tc.c" &&
+	# One commit changes func1 and func2; MAGIC lands only in the
+	# func2 change, outside func1.
+	sed -e "s/F1/F1 + 1/" -e "s/return F2/return MAGIC/" tc.c >tmp &&
+	mv tmp tc.c &&
+	git commit -a -m "change both funcs" &&
+	echo "tc.c diff=tc" >.gitattributes &&
+
+	# Without a textconv driver, -G is scoped to func1, so MAGIC (only
+	# in the func2 change) does not select the commit.
+	git log -L:func1:tc.c -G MAGIC --format=%s --no-patch >actual &&
+	test_must_be_empty actual &&
+
+	# A textconv driver makes the range (original-file line numbers)
+	# meaningless against the driver output, so -G falls back to the
+	# whole file and MAGIC now selects the commit.
+	git config diff.tc.textconv cat &&
+	git log -L:func1:tc.c -G MAGIC --format=%s --no-patch >actual &&
+	test_grep "change both funcs" actual
+'
+
 test_done
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 51c88296ed..71e5dffefb 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -46,6 +46,19 @@ int xdi_diff_outf(mmfile_t *mf1, mmfile_t *mf2,
 		  xdiff_emit_line_fn line_fn,
 		  void *consume_callback_data,
 		  xpparam_t const *xpp, xdemitconf_t const *xecfg);
+
+struct range_set;
+/*
+ * Like xdi_diff_outf(), but forwards only the lines within the given
+ * (post-image) line ranges to line_fn, as "git log -L" scopes its output.
+ * Returns line_fn's latched return value (so a consumer can signal a hit
+ * with a non-zero return), or non-zero on xdiff failure.  Defined in
+ * diff.c (it reuses the line-range filter there).
+ */
+int diff_emit_line_ranges(mmfile_t *mf1, mmfile_t *mf2,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg);
 int read_mmfile(mmfile_t *ptr, const char *filename);
 void read_mmblob(mmfile_t *ptr, struct object_database *odb,
 		 const struct object_id *oid);
-- 
gitgitgadget

Re: [PATCH 5/7] line-log: support diff stat formats with -L

[Junio C Hamano]

"Michael Montalbo via GitGitGadget" <gitgitgadget@gmail.com> writes:

> diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
> index 72f639b5e7..1a25f55bb1 100644
> --- a/Documentation/line-range-options.adoc
> +++ b/Documentation/line-range-options.adoc
> @@ -9,10 +9,14 @@
>  	_<start>_ and _<end>_ (or _<funcname>_) must exist in the starting revision.
>  	You can specify this option more than once. Implies `--patch`.
>  	Patch output can be suppressed using `--no-patch`.
> -	Non-patch diff formats `--raw`, `--name-only`, `--name-status`,
> -	and `--summary` are supported.  Diff stat formats
> -	(`--stat`, `--numstat`, `--shortstat`, `--dirstat`) are not
> -	currently implemented.
> +	The following non-patch diff formats are supported: `--raw`,
> +	`--name-only`, `--name-status`, `--summary`,
> +	`--stat`, `--numstat`, and `--shortstat`.
> +	The stat formats show range-scoped counts: only lines within
> +	the tracked range are counted.  `--dirstat` is not supported

If "range-scoped" is a widely known term (as opposed to a new word
invented only during the introduction of this topic), the above
reads well with a nice rhythm, but otherwise it may be easier to
read, i.e., something like

	The stat formats counts only lines within the tracked range.

without having readers learn yet another new term that is only used
here.

> diff --git a/diff.c b/diff.c
> index 6233a96bf0..026fafeb90 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -4289,7 +4289,18 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
>  		xecfg.ctxlen = o->context;
>  		xecfg.interhunkctxlen = o->interhunkcontext;
>  		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
> -		if (xdi_diff_outf(&mf1, &mf2, NULL,
> +
> +		if (p->line_ranges) {
> +			struct line_range_filter lr_filter;
> +
> +			line_range_filter_init(&lr_filter, p->line_ranges,
> +					       diffstat_consume, diffstat);
> +
> +			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
> +						   &xpp, &xecfg))
> +				die("unable to generate diffstat for %s",
> +				    one->path);
> +		} else if (xdi_diff_outf(&mf1, &mf2, NULL,
>  				  diffstat_consume, diffstat, &xpp, &xecfg))
>  			die("unable to generate diffstat for %s", one->path);

It is pleasing to see that this can be done with such a surprisingly
small change.

Re: [PATCH 5/7] line-log: support diff stat formats with -L

[Michael Montalbo]

On Thu, Jun 18, 2026 at 3:00 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> If "range-scoped" is a widely known term (as opposed to a new word
> invented only during the introduction of this topic), the above
> reads well with a nice rhythm, but otherwise it may be easier to
> read, i.e., something like
>
>         The stat formats counts only lines within the tracked range.
>
> without having readers learn yet another new term that is only used
> here.
>

It was something I invented for the topic, but I agree it is better to
avoid coining a new term, especially since it ends up being spelled
out anyway in the blurb that follows. Will replace the term.

> > diff --git a/diff.c b/diff.c
> > index 6233a96bf0..026fafeb90 100644
> > --- a/diff.c
> > +++ b/diff.c
> > @@ -4289,7 +4289,18 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
> >               xecfg.ctxlen = o->context;
> >               xecfg.interhunkctxlen = o->interhunkcontext;
> >               xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
> > -             if (xdi_diff_outf(&mf1, &mf2, NULL,
> > +
> > +             if (p->line_ranges) {
> > +                     struct line_range_filter lr_filter;
> > +
> > +                     line_range_filter_init(&lr_filter, p->line_ranges,
> > +                                            diffstat_consume, diffstat);
> > +
> > +                     if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
> > +                                                &xpp, &xecfg))
> > +                             die("unable to generate diffstat for %s",
> > +                                 one->path);
> > +             } else if (xdi_diff_outf(&mf1, &mf2, NULL,
> >                                 diffstat_consume, diffstat, &xpp, &xecfg))
> >                       die("unable to generate diffstat for %s", one->path);
>
> It is pleasing to see that this can be done with such a surprisingly
> small change.
>

Agreed! I didn't initially plan it out that way during the first series,
but things fell into place nicely by the end.

[PATCH v2 0/7] line-log: scope stat, check, and -G to -L line ranges

[Michael Montalbo via GitGitGadget]

This series extends git log -L so that more of its diff output and commit
selection honor the tracked line ranges: the diff stat formats and --check
report only the lines inside the tracked range, and the -G pickaxe is scoped
to the tracked range.

It builds on top of the mm/line-log-cleanup topic [1], which integrated -L
with the standard log output pipeline and taught it the non-patch formats
--raw, --name-only, --name-status, and --summary.

With these patches the following also honor the tracked range:

 * --stat, --numstat, --shortstat: counts cover only the lines inside the
   tracked range, not the whole file.

 * --check: whitespace errors are reported only for added lines inside the
   tracked range, with the correct file line numbers.

 * -G: a commit is selected only when the pattern appears on an
   added/removed line inside the tracked range, rather than anywhere in the
   file.

The --dirstat format is deliberately rejected. Its default mode reports each
directory's share of the total churn as a percentage, computed from
whole-file byte damage (via diffcore_count_changes(), outside the line-based
pipeline that -L scopes), so bare --dirstat cannot honor the tracked range.
The --dirstat=lines mode could: it aggregates the same per-file line counts
as --numstat, which -L already scopes. But supporting only that sub-mode
while bare --dirstat still errors is a confusing split, so the whole format
is left to a follow-up; --numstat already gives the exact per-file counts
within the tracked range.

-S is left matching the whole file. Unlike -G, it counts needle occurrences
per blob rather than grepping the diff, so scoping it to a range needs a
different approach; that is left to a follow-up. Patch 7, which scopes -G,
also updates the -L documentation to note the -S/-G distinction, so the
whole-file behavior of -S is not mistaken for the way -G is scoped to the
tracked range.

Patches 1-3 are independent of the new formats: they fix two bugs in the
existing -L patch output (a leaked deletion and an off-by-one hunk header),
bring its hunk headers in line with git diff's format, and clarify the
line-range filter mm/line-log-cleanup added, whose names obscured its model
(cryptic lno_ cursors conflating the pre/post-image and 0/1-based axes, a
flat hunk-state struct, and a one-letter state pointer (s)). The two bugs
may be a hint that the model could use clarification, so patch 1 renames and
groups the filter state and patch 2 documents the model, before the fixes
that read against it. Patches 4-7 then build the new formats on top:

 * Patch 1: rename and group the filter for clarity. Spell the cryptic names
   out to the file's own forms: the line-number cursors to
   lno_in_preimage/lno_in_postimage (as in struct emit_callback) and the
   range index to idx_in_postimage, while the hunk geometry stays old/new
   (the xdiff_emit_hunk_fn convention) and moves into a sub-struct. Name the
   filter pointer (filter) and rename the struct to line_range_filter and
   the flush helper to flush_range_hunk. No behavior change.

 * Patch 2: simplify the filter by classifying removals as they arrive,
   dropping the pending_rm buffer and a latent flush_range_hunk() bug that
   leaked deletions just past the range. Make the buffered lines the hunk's
   single source of truth: flush_range_hunk() derives the counts from them
   rather than tracking them per line, dropping three more fields. Document
   the model with a block comment and worked example, and add
   begin_range_hunk() as the counterpart to flush_range_hunk(). (This
   simplification was submitted by itself previously [2] but did not
   advance, so it is re-included here.)

 * Patch 3: stop hand-rolling the synthetic hunk header and emit it through
   xdiff's own formatter via a new xdiff_emit_hunk_header() helper. The
   hand-rolled code put a count-0 side's begin one too high (the convention
   is the line before the change); routing through xdl_emit_hunk_hdr() fixes
   that by construction and, as a side effect, makes -L headers match git
   diff exactly, including its omission of a count of 1. Regenerate the two
   affected fixtures.

 * Patch 4: extract a line_range_filter_diff() helper that folds the
   filter's two preconditions into one place: inflate ctxlen to the largest
   range span so every change within a range lands in a single xdiff hunk,
   and clear XDL_EMIT_NO_HUNK_HDR so the hunk headers the filter reads are
   always emitted (its position tracking relies on both). It then runs an
   initialized filter through xdiff, flushes the final range hunk, and
   releases it; use it in builtin_diff(). The stat, check, and -G patches
   that reuse it inherit both.

 * Patch 5: reuse the filter in builtin_diffstat() for the stat formats,
   extend the -L output-format allowlist, and reject --dirstat.

 * Patch 6: reuse the filter in builtin_checkdiff() and extend the allowlist
   for --check. The separate blank-at-eof pass scans the whole file, so
   scope its report to the tracked ranges too.

 * Patch 7: scope -G to the tracked range. Expose the filter as
   diff_emit_line_ranges() and grep only the tracked range's lines,
   threading the filepair's line_ranges through the pickaxe callback. -S is
   left whole-file, and the -L documentation is updated to note that -G is
   scoped to the tracked range while -S still matches the whole file.

Changes since v1:

 * Replace the term "range-scoped" with explicit descriptions that refer to
   "tracked line ranges" instead.

[1]
https://lore.kernel.org/git/pull.2094.v3.git.1780001267.gitgitgadget@gmail.com/
[2]
https://lore.kernel.org/git/pull.2099.git.1777230630020.gitgitgadget@gmail.com/

Michael Montalbo (7):
  diff: rename and group the line-range filter for clarity
  diff: simplify the line-range filter by classifying removals
    immediately
  diff: emit -L hunk headers via xdiff's formatter
  diff: extract a line-range diff helper for reuse
  line-log: support diff stat formats with -L
  diff: support --check with -L line ranges
  diffcore-pickaxe: scope -G to the -L tracked range

 Documentation/line-range-options.adoc    |  17 +-
 diff.c                                   | 491 ++++++++++++++---------
 diffcore-pickaxe.c                       |  37 +-
 revision.c                               |   6 +-
 t/t4211-line-log.sh                      | 439 +++++++++++++++++++-
 t/t4211/sha1/expect.no-assertion-error   |   2 +-
 t/t4211/sha1/expect.vanishes-early       |   6 +-
 t/t4211/sha256/expect.no-assertion-error |   2 +-
 t/t4211/sha256/expect.vanishes-early     |   6 +-
 xdiff-interface.c                        |  19 +
 xdiff-interface.h                        |  28 ++
 11 files changed, 826 insertions(+), 227 deletions(-)


base-commit: ea97ad8d017de0c9037451a78008a0fd60abea0c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2152%2Fmmontalbo%2Fmm%2Fline-log-stat-formats-followup-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2152/mmontalbo/mm/line-log-stat-formats-followup-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/2152

Range-diff vs v1:

 1:  6cfaccab92 = 1:  6cfaccab92 diff: rename and group the line-range filter for clarity
 2:  5602b7976a = 2:  5602b7976a diff: simplify the line-range filter by classifying removals immediately
 3:  d211c82e40 = 3:  d211c82e40 diff: emit -L hunk headers via xdiff's formatter
 4:  b82a997359 = 4:  b82a997359 diff: extract a line-range diff helper for reuse
 5:  a70d861d27 ! 5:  3d0091b549 line-log: support diff stat formats with -L
     @@ Metadata
       ## Commit message ##
          line-log: support diff stat formats with -L
      
     -    Reuse the line_range_filter in builtin_diffstat() to produce
     -    range-scoped statistics.  When a filepair carries line_ranges, the
     -    filter wraps diffstat_consume() as its output callback, forwarding only
     -    in-range lines for counting.  flush_range_hunk() replays buffered
     -    content through diffstat_consume(), which ignores synthetic @@ headers
     -    since it only counts '+' and '-' lines.
     +    Reuse the line_range_filter in builtin_diffstat() so the stat formats
     +    count only the lines within the tracked range.  When a filepair carries
     +    line_ranges, the filter wraps diffstat_consume() as its output callback,
     +    forwarding only the lines inside the range for counting.
     +    flush_range_hunk() replays buffered content through diffstat_consume(),
     +    which ignores synthetic @@ headers since it only counts '+' and '-'
     +    lines.
      
          Expand the output format allowlist in setup_revisions() to accept
          --stat, --numstat, and --shortstat with -L.
     @@ Commit message
          per-file line counts as --numstat, which -L already scopes.  But
          accepting only that sub-mode while bare --dirstat keeps erroring is a
          confusing split, so the whole format is deferred to a follow-up;
     -    --numstat already reports the exact range-scoped per-file counts.
     +    --numstat already reports the exact per-file counts within the tracked
     +    range.
      
          Also drop "yet" from the generic -L rejection message ("does not
          yet support the requested diff format").  Some rejected formats do
     @@ Documentation/line-range-options.adoc
      +	The following non-patch diff formats are supported: `--raw`,
      +	`--name-only`, `--name-status`, `--summary`,
      +	`--stat`, `--numstat`, and `--shortstat`.
     -+	The stat formats show range-scoped counts: only lines within
     -+	the tracked range are counted.  `--dirstat` is not supported
     ++	The stat formats count only lines within the tracked range.
     ++	`--dirstat` is not supported
      +	with `-L`: it summarizes change as each directory's share of
      +	the total churn, not as counts for the tracked lines.  Use
      +	`--numstat` for exact per-file counts within the range.
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +	git commit -m "Add func1() and func2()" &&
      +
      +	# Modify both functions in a single commit so that
     -+	# whole-file stats differ from range-scoped stats.
     ++	# whole-file stats differ from the counts for the tracked range.
      +	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" file.c >tmp &&
      +	mv tmp file.c &&
      +	git commit -a -m "Modify both functions"
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +test_expect_success '--numstat counts only lines in tracked range' '
      +	# "Modify both functions" changes one line in func1 and one in
      +	# func2.  Whole-file numstat would show 2 added, 2 deleted.
     -+	# Range-scoped numstat for func2 should show only 1 and 1.
     ++	# numstat for func2 within the tracked range should show only 1 and 1.
      +	git log -L:func2:file.c --numstat --format=%s -1 >actual &&
      +	test_grep "Modify both functions" actual &&
      +	test_grep "^1	1	file.c$" actual &&
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +
      +test_expect_success '--numstat counts only additions for root commit' '
      +	# Root commit creates both func1 (4 lines) and func2 (4 lines).
     -+	# Whole-file numstat would show 9 lines added.  Range-scoped
     -+	# numstat for func2 should show only 4.
     ++	# Whole-file numstat would show 9 lines added.  numstat for func2
     ++	# within the tracked range should show only 4.
      +	git log -L:func2:file.c --numstat --format=%s >actual &&
      +	test_grep "Add func1() and func2()" actual &&
      +	test_grep "^4	0	file.c$" actual &&
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +
      +test_expect_success '--shortstat counts only lines in tracked range' '
      +	# --shortstat prints only the summary line: no per-file "file.c |"
     -+	# line.  Counts are range-scoped as for --numstat above.
     ++	# line.  Counts cover only the tracked range, as for --numstat above.
      +	git log -L:func2:file.c --shortstat --format=%s -1 >actual &&
      +	test_grep "Modify both functions" actual &&
      +	test_grep "1 insertion" actual &&
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +test_expect_success '--numstat across renames and multiple commits' '
      +	# parallel-change carries the tracked function f across an a.c -> b.c
      +	# rename and a merge of two parallel histories.  With -M, --numstat
     -+	# follows the rename and reports range-scoped (not whole-file)
     -+	# added/removed counts for f per commit; the file column flips from
     ++	# follows the rename and reports added/removed counts for f within
     ++	# the tracked range (not whole-file) per commit; the file column flips from
      +	# b.c to a.c at the rename as the walk goes back in time.  Commits
      +	# that do not change the range of f emit no row (the merge and the
      +	# pure file-move produce nothing), so there are fewer rows than
 6:  be0679a5a7 ! 6:  36ed52d831 diff: support --check with -L line ranges
     @@ Documentation/line-range-options.adoc
      -	`--name-only`, `--name-status`, `--summary`,
      +	`--name-only`, `--name-status`, `--summary`, `--check`,
       	`--stat`, `--numstat`, and `--shortstat`.
     - 	The stat formats show range-scoped counts: only lines within
     - 	the tracked range are counted.  `--dirstat` is not supported
     + 	The stat formats count only lines within the tracked range.
     + 	`--dirstat` is not supported
      
       ## diff.c ##
      @@ diff.c: struct emit_callback {
 7:  f69ccfbc8c ! 7:  df83e6275b diffcore-pickaxe: scope -G to the -L tracked range
     @@ Commit message
          Teach -G to honor the range.  diff_grep() already runs an xdiff pass
          and greps the +/- lines; route that pass through the line-range filter
          so only the tracked range's lines are grepped.  Expose the filter as
     -    diff_emit_line_ranges(), a line-range-scoped xdi_diff_outf(), thread
     -    the filepair's line_ranges through the pickaxe callback, and pass it
     -    from pickaxe_match().  Skip scoping under textconv, whose output is not
     -    in the original file's line coordinates.
     +    diff_emit_line_ranges(), an xdi_diff_outf() that emits only the tracked
     +    range's lines, thread the filepair's line_ranges through the pickaxe
     +    callback, and pass it from pickaxe_match().  Skip scoping under
     +    textconv, whose output is not in the original file's line coordinates.
      
          -G needs only a hit/no-hit answer, so the line-number concerns the
          filter handles for patch and check output do not apply here.
     @@ Commit message
          approach, left to a follow-up.  has_changes() takes the range parameter
          but ignores it for now.
      
     -    Document the resulting -L pickaxe scoping: -G is range-scoped, while -S
     -    still matches the whole file.
     +    Document the resulting -L pickaxe scoping: -G is scoped to the tracked
     +    range, while -S still matches the whole file.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      

-- 
gitgitgadget

[PATCH v2 1/7] diff: rename and group the line-range filter for clarity

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

The line-range filter that mm/line-log-cleanup added uses names that
obscure its model.  The cursors lno_post/lno_pre and the index lno_0
share an lno_ prefix but conflate the pre/post-image axis with the
0-based/1-based axis, the hunk state is a flat set of rhunk_* fields,
and the filter-state pointer is just s.

The filter bridges two layers of diff.c, and its fields already used
each layer's vocabulary, but in cryptic abbreviations.  Spell them out
to the form the rest of the file uses, so that the patches that follow
can simplify and fix it with those clearer names in place:

  - lno_post/lno_pre -> lno_in_postimage/lno_in_preimage, the
    line-number cursors, matching the counters in struct emit_callback
  - lno_0 -> idx_in_postimage, the 0-based range index
  - the hunk-header geometry stays old/new (old_begin, new_begin, and
    counts) to match the xdiff_emit_hunk_fn callback and the
    "@@ -<old> +<new> @@" header it feeds, but moves from flat rhunk_*
    fields into a "hunk" sub-struct, so accesses read
    filter->hunk.old_begin
  - flush_rhunk -> flush_range_hunk
  - the filter-state pointer in each callback: s -> filter

Also rename the struct line_range_callback to line_range_filter: it is
a filter over xdiff output, not merely a callback.

No behavior change.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c | 192 +++++++++++++++++++++++++++++----------------------------
 1 file changed, 97 insertions(+), 95 deletions(-)

diff --git a/diff.c b/diff.c
index 5a584fa1d5..1e043c959f 100644
--- a/diff.c
+++ b/diff.c
@@ -623,15 +623,15 @@ struct emit_callback {
  * reveals whether they precede an in-range line (flush into range hunk) or
  * an out-of-range line (discard).
  */
-struct line_range_callback {
+struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
 	void *orig_cb_data;
 	const struct range_set *ranges;	/* 0-based [start, end) */
 	unsigned int cur_range;		/* index into the range_set */
 
 	/* Post/pre-image line counters (1-based, set from hunk headers) */
-	long lno_post;
-	long lno_pre;
+	long lno_in_postimage;
+	long lno_in_preimage;
 
 	/*
 	 * Function name from most recent xdiff hunk header;
@@ -640,12 +640,14 @@ struct line_range_callback {
 	char func[80];
 	long funclen;
 
-	/* Range hunk being accumulated for the current range */
-	struct strbuf rhunk;
-	long rhunk_old_begin, rhunk_old_count;
-	long rhunk_new_begin, rhunk_new_count;
-	int rhunk_active;
-	int rhunk_has_changes;		/* any '+' or '-' lines? */
+	/* The range hunk being accumulated for the current range. */
+	struct {
+		struct strbuf lines;	/* buffered in-range diff lines */
+		long old_begin, old_count;
+		long new_begin, new_count;
+		int active;
+		int has_changes;	/* any '+' or '-' line? */
+	} hunk;
 
 	/* Removal lines not yet known to be in-range */
 	struct strbuf pending_rm;
@@ -2540,26 +2542,26 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
-static void discard_pending_rm(struct line_range_callback *s)
+static void discard_pending_rm(struct line_range_filter *filter)
 {
-	strbuf_reset(&s->pending_rm);
-	s->pending_rm_count = 0;
+	strbuf_reset(&filter->pending_rm);
+	filter->pending_rm_count = 0;
 }
 
-static void flush_rhunk(struct line_range_callback *s)
+static void flush_range_hunk(struct line_range_filter *filter)
 {
 	struct strbuf hdr = STRBUF_INIT;
 	const char *p, *end;
 
-	if (!s->rhunk_active || s->ret)
+	if (!filter->hunk.active || filter->ret)
 		return;
 
 	/* Drain any pending removal lines into the range hunk */
-	if (s->pending_rm_count) {
-		strbuf_addbuf(&s->rhunk, &s->pending_rm);
-		s->rhunk_old_count += s->pending_rm_count;
-		s->rhunk_has_changes = 1;
-		discard_pending_rm(s);
+	if (filter->pending_rm_count) {
+		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
+		filter->hunk.old_count += filter->pending_rm_count;
+		filter->hunk.has_changes = 1;
+		discard_pending_rm(filter);
 	}
 
 	/*
@@ -2568,22 +2570,22 @@ static void flush_rhunk(struct line_range_callback *s)
 	 * ctxlen causes xdiff to emit context covering a range that
 	 * has no changes in this commit.
 	 */
-	if (!s->rhunk_has_changes) {
-		s->rhunk_active = 0;
-		strbuf_reset(&s->rhunk);
+	if (!filter->hunk.has_changes) {
+		filter->hunk.active = 0;
+		strbuf_reset(&filter->hunk.lines);
 		return;
 	}
 
 	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    s->rhunk_old_begin, s->rhunk_old_count,
-		    s->rhunk_new_begin, s->rhunk_new_count);
-	if (s->funclen > 0) {
+		    filter->hunk.old_begin, filter->hunk.old_count,
+		    filter->hunk.new_begin, filter->hunk.new_count);
+	if (filter->funclen > 0) {
 		strbuf_addch(&hdr, ' ');
-		strbuf_add(&hdr, s->func, s->funclen);
+		strbuf_add(&hdr, filter->func, filter->funclen);
 	}
 	strbuf_addch(&hdr, '\n');
 
-	s->ret = s->orig_line_fn(s->orig_cb_data, hdr.buf, hdr.len);
+	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
 
 	/*
@@ -2591,18 +2593,18 @@ static void flush_rhunk(struct line_range_callback *s)
 	 * The cast discards const because xdiff_emit_line_fn takes
 	 * char *, though fn_out_consume does not modify the buffer.
 	 */
-	p = s->rhunk.buf;
-	end = p + s->rhunk.len;
-	while (!s->ret && p < end) {
+	p = filter->hunk.lines.buf;
+	end = p + filter->hunk.lines.len;
+	while (!filter->ret && p < end) {
 		const char *eol = memchr(p, '\n', end - p);
 		unsigned long line_len = eol ? (unsigned long)(eol - p + 1)
 					     : (unsigned long)(end - p);
-		s->ret = s->orig_line_fn(s->orig_cb_data, (char *)p, line_len);
+		filter->ret = filter->orig_line_fn(filter->orig_cb_data, (char *)p, line_len);
 		p += line_len;
 	}
 
-	s->rhunk_active = 0;
-	strbuf_reset(&s->rhunk);
+	filter->hunk.active = 0;
+	strbuf_reset(&filter->hunk.lines);
 }
 
 static void line_range_hunk_fn(void *data,
@@ -2610,7 +2612,7 @@ static void line_range_hunk_fn(void *data,
 			       long new_begin, long new_nr UNUSED,
 			       const char *func, long funclen)
 {
-	struct line_range_callback *s = data;
+	struct line_range_filter *filter = data;
 
 	/*
 	 * When count > 0, begin is 1-based.  When count == 0, begin is
@@ -2622,104 +2624,104 @@ static void line_range_hunk_fn(void *data,
 	 * flush or discard them when the next content line reveals
 	 * whether the removals precede in-range content.
 	 */
-	s->lno_post = new_begin;
-	s->lno_pre = old_begin;
+	filter->lno_in_postimage = new_begin;
+	filter->lno_in_preimage = old_begin;
 
 	if (funclen > 0) {
-		if (funclen > (long)sizeof(s->func))
-			funclen = sizeof(s->func);
-		memcpy(s->func, func, funclen);
+		if (funclen > (long)sizeof(filter->func))
+			funclen = sizeof(filter->func);
+		memcpy(filter->func, func, funclen);
 	}
-	s->funclen = funclen;
+	filter->funclen = funclen;
 }
 
 static int line_range_line_fn(void *priv, char *line, unsigned long len)
 {
-	struct line_range_callback *s = priv;
+	struct line_range_filter *filter = priv;
 	const struct range *cur;
-	long lno_0, cur_pre;
+	long idx_in_postimage, cur_pre;
 
-	if (s->ret)
-		return s->ret;
+	if (filter->ret)
+		return filter->ret;
 
 	if (line[0] == '-') {
-		if (!s->pending_rm_count)
-			s->pending_rm_pre_begin = s->lno_pre;
-		s->lno_pre++;
-		strbuf_add(&s->pending_rm, line, len);
-		s->pending_rm_count++;
-		return s->ret;
+		if (!filter->pending_rm_count)
+			filter->pending_rm_pre_begin = filter->lno_in_preimage;
+		filter->lno_in_preimage++;
+		strbuf_add(&filter->pending_rm, line, len);
+		filter->pending_rm_count++;
+		return filter->ret;
 	}
 
 	if (line[0] == '\\') {
-		if (s->pending_rm_count)
-			strbuf_add(&s->pending_rm, line, len);
-		else if (s->rhunk_active)
-			strbuf_add(&s->rhunk, line, len);
+		if (filter->pending_rm_count)
+			strbuf_add(&filter->pending_rm, line, len);
+		else if (filter->hunk.active)
+			strbuf_add(&filter->hunk.lines, line, len);
 		/* otherwise outside tracked range; drop silently */
-		return s->ret;
+		return filter->ret;
 	}
 
 	if (line[0] != '+' && line[0] != ' ')
 		BUG("unexpected diff line type '%c'", line[0]);
 
-	lno_0 = s->lno_post - 1;
-	cur_pre = s->lno_pre;	/* save before advancing for context lines */
-	s->lno_post++;
+	idx_in_postimage = filter->lno_in_postimage - 1;
+	cur_pre = filter->lno_in_preimage;	/* save before advancing for context lines */
+	filter->lno_in_postimage++;
 	if (line[0] == ' ')
-		s->lno_pre++;
+		filter->lno_in_preimage++;
 
 	/* Advance past ranges we've passed */
-	while (s->cur_range < s->ranges->nr &&
-	       lno_0 >= s->ranges->ranges[s->cur_range].end) {
-		if (s->rhunk_active)
-			flush_rhunk(s);
-		discard_pending_rm(s);
-		s->cur_range++;
+	while (filter->cur_range < filter->ranges->nr &&
+	       idx_in_postimage >= filter->ranges->ranges[filter->cur_range].end) {
+		if (filter->hunk.active)
+			flush_range_hunk(filter);
+		discard_pending_rm(filter);
+		filter->cur_range++;
 	}
 
 	/* Past all ranges */
-	if (s->cur_range >= s->ranges->nr) {
-		discard_pending_rm(s);
-		return s->ret;
+	if (filter->cur_range >= filter->ranges->nr) {
+		discard_pending_rm(filter);
+		return filter->ret;
 	}
 
-	cur = &s->ranges->ranges[s->cur_range];
+	cur = &filter->ranges->ranges[filter->cur_range];
 
 	/* Before current range */
-	if (lno_0 < cur->start) {
-		discard_pending_rm(s);
-		return s->ret;
+	if (idx_in_postimage < cur->start) {
+		discard_pending_rm(filter);
+		return filter->ret;
 	}
 
 	/* In range so start a new range hunk if needed */
-	if (!s->rhunk_active) {
-		s->rhunk_active = 1;
-		s->rhunk_has_changes = 0;
-		s->rhunk_new_begin = lno_0 + 1;
-		s->rhunk_old_begin = s->pending_rm_count
-			? s->pending_rm_pre_begin : cur_pre;
-		s->rhunk_old_count = 0;
-		s->rhunk_new_count = 0;
-		strbuf_reset(&s->rhunk);
+	if (!filter->hunk.active) {
+		filter->hunk.active = 1;
+		filter->hunk.has_changes = 0;
+		filter->hunk.new_begin = idx_in_postimage + 1;
+		filter->hunk.old_begin = filter->pending_rm_count
+			? filter->pending_rm_pre_begin : cur_pre;
+		filter->hunk.old_count = 0;
+		filter->hunk.new_count = 0;
+		strbuf_reset(&filter->hunk.lines);
 	}
 
 	/* Flush pending removals into range hunk */
-	if (s->pending_rm_count) {
-		strbuf_addbuf(&s->rhunk, &s->pending_rm);
-		s->rhunk_old_count += s->pending_rm_count;
-		s->rhunk_has_changes = 1;
-		discard_pending_rm(s);
+	if (filter->pending_rm_count) {
+		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
+		filter->hunk.old_count += filter->pending_rm_count;
+		filter->hunk.has_changes = 1;
+		discard_pending_rm(filter);
 	}
 
-	strbuf_add(&s->rhunk, line, len);
-	s->rhunk_new_count++;
+	strbuf_add(&filter->hunk.lines, line, len);
+	filter->hunk.new_count++;
 	if (line[0] == '+')
-		s->rhunk_has_changes = 1;
+		filter->hunk.has_changes = 1;
 	else
-		s->rhunk_old_count++;
+		filter->hunk.old_count++;
 
-	return s->ret;
+	return filter->ret;
 }
 
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
@@ -4086,7 +4088,7 @@ static void builtin_diff(const char *name_a,
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
 		} else if (line_ranges) {
-			struct line_range_callback lr_state;
+			struct line_range_filter lr_state;
 			unsigned int i;
 			long max_span = 0;
 
@@ -4094,7 +4096,7 @@ static void builtin_diff(const char *name_a,
 			lr_state.orig_line_fn = fn_out_consume;
 			lr_state.orig_cb_data = &ecbdata;
 			lr_state.ranges = line_ranges;
-			strbuf_init(&lr_state.rhunk, 0);
+			strbuf_init(&lr_state.hunk.lines, 0);
 			strbuf_init(&lr_state.pending_rm, 0);
 
 			/*
@@ -4125,11 +4127,11 @@ static void builtin_diff(const char *name_a,
 				die("unable to generate diff for %s",
 				    one->path);
 
-			flush_rhunk(&lr_state);
+			flush_range_hunk(&lr_state);
 			if (lr_state.ret)
 				die("unable to generate diff for %s",
 				    one->path);
-			strbuf_release(&lr_state.rhunk);
+			strbuf_release(&lr_state.hunk.lines);
 			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
-- 
gitgitgadget

[PATCH v2 2/7] diff: simplify the line-range filter by classifying removals immediately

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

The filter buffered '-' lines in a pending_rm strbuf, deferring their
classification until a '+' or ' ' line revealed the post-image
position.  That buffering is unnecessary: a removal occupies no
post-image line, so it does not advance lno_in_postimage, and xdiff
emits removals before additions within a change.  A '-' therefore
arrives while lno_in_postimage already holds the index the following
'+'/' ' will occupy, and can be classified against the ranges as it
arrives.

The buffering also hid a bug: flush_range_hunk() drained pending_rm into
the range hunk whenever the hunk was active, even after lno_in_postimage
had advanced past the tracked range, so a deletion just after the
tracked function leaked into the patch.  Classifying each line as it
arrives removes the pending_rm buffer, the discard_pending_rm() helper,
three struct fields, and makes that bug impossible by construction.

With every line classified on arrival, the buffered lines are the
hunk's single source of truth, so the old/new counts need not be kept
alongside them: flush_range_hunk() derives the counts (and whether the
hunk holds any change) from the buffer when it builds the header.  Drop
the per-line counting and the old_count, new_count, and has_changes
fields; there is no longer a second tally that could fall out of sync
with the buffer.

Add begin_range_hunk() to open the accumulator at the first in-range
line, seeding both begins from the live image cursors, as the
counterpart to flush_range_hunk().  With the counting gone too,
line_range_line_fn() now only appends an in-range line.

Document the coordinate model: a block comment on struct
line_range_filter states it (the pre/post-image cursors, the 0-based
idx_in_postimage, removals classified by the following line) with a
worked example.

Add tests for the leaked trailing deletion this fixes, the symmetric
leading-deletion case, and the filter's range boundaries (a change at
the first and last line of a range, and a pure in-range deletion).

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c              | 215 ++++++++++++++++++++++++--------------------
 t/t4211-line-log.sh | 125 ++++++++++++++++++++++++++
 2 files changed, 243 insertions(+), 97 deletions(-)

diff --git a/diff.c b/diff.c
index 1e043c959f..ee765d7ac2 100644
--- a/diff.c
+++ b/diff.c
@@ -610,18 +610,58 @@ struct emit_callback {
 };
 
 /*
- * State for the line-range callback wrappers that sit between
- * xdi_diff_outf() and fn_out_consume().  xdiff produces a normal,
- * unfiltered diff; the wrappers intercept each hunk header and line,
- * track post-image position, and forward only lines that fall within
- * the requested ranges.  Contiguous in-range lines are collected into
- * range hunks and flushed with a synthetic @@ header so that
- * fn_out_consume() sees well-formed unified-diff fragments.
+ * Line-range filter: scopes "git log -L" output to the tracked ranges.
  *
- * Removal lines ('-') cannot be classified by post-image position, so
- * they are buffered in pending_rm until the next '+' or ' ' line
- * reveals whether they precede an in-range line (flush into range hunk) or
- * an out-of-range line (discard).
+ * It sits between xdi_diff_outf() and an output callback (fn_out_consume,
+ * diffstat_consume, checkdiff_consume).  xdiff produces a normal diff; the
+ * filter forwards only the lines inside the requested ranges, collecting
+ * contiguous in-range lines into a "range hunk" emitted with a synthetic
+ * @@ header so the callback sees well-formed unified-diff fragments.
+ *
+ * A diff describes the change from a pre-image to a post-image.  Each
+ * line is context (' ', in both), a removal ('-', pre-image only), or
+ * an addition ('+', post-image only).  -L tracks ranges in the
+ * post-image, so a line is in range by its post-image position.
+ *
+ * Two 1-based cursors track the next line in each image, named as in
+ * struct emit_callback and seeded from the xdiff hunk header:
+ *
+ *	lno_in_postimage  advances on '+' and ' '   (lines in the post-image)
+ *	lno_in_preimage   advances on '-' and ' '   (lines in the pre-image)
+ *
+ * Ranges are 0-based half-open [start, end), so a line is tested at the
+ * 0-based index idx_in_postimage = lno_in_postimage - 1.
+ *
+ * A '-' is not present in the post-image, so it has no post-image line
+ * number of its own.  Since it does not advance lno_in_postimage, it is
+ * classified at the idx_in_postimage that the following '+'/' ' will
+ * occupy.  xdiff emits a change's removals before its additions, so that
+ * index is already known when the '-' arrives.
+ *
+ * The synthetic "@@ -<old> +<new> @@" header has two sides, old (the
+ * pre-image) and new (the post-image), matching the xdiff_emit_hunk_fn
+ * callback; the hunk.old_begin / hunk.new_begin fields below hold those
+ * begins, and flush_range_hunk() derives the counts from the buffered
+ * lines.
+ *
+ * Example, tracking post-image line 2 (range [1, 2)) of:
+ *
+ *	pre-image  post-image
+ *	1 a        1 a
+ *	2 b        2 X      (b -> X)
+ *	3 c        3 c
+ *
+ *	classify each line by idx_in_postimage.  The pre and post columns
+ *	are each cursor's value while that line is classified, i.e. before
+ *	the line advances them (pre = lno_in_preimage,
+ *	post = lno_in_postimage, idx = idx_in_postimage):
+ *	' a'  pre 1  post 1  idx 0  ->  before start, skip
+ *	'-b'  pre 2  post 2  idx 1  ->  keep (removal)
+ *	'+X'  pre 3  post 2  idx 1  ->  keep (addition)
+ *	' c'  pre 3  post 3  idx 2  ->  past end, flush
+ *
+ * -b and +X share idx = 1 because -b did not advance lno_in_postimage;
+ * both land in the range hunk, flushed when ' c' crosses the range end.
  */
 struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
@@ -640,20 +680,18 @@ struct line_range_filter {
 	char func[80];
 	long funclen;
 
-	/* The range hunk being accumulated for the current range. */
+	/*
+	 * The range hunk being accumulated.  At most one is live at a time:
+	 * it is flushed and reset as the cursor leaves each range (and once
+	 * more at end of diff), then reused for the next range.
+	 */
 	struct {
 		struct strbuf lines;	/* buffered in-range diff lines */
-		long old_begin, old_count;
-		long new_begin, new_count;
+		long old_begin;
+		long new_begin;
 		int active;
-		int has_changes;	/* any '+' or '-' line? */
 	} hunk;
 
-	/* Removal lines not yet known to be in-range */
-	struct strbuf pending_rm;
-	int pending_rm_count;
-	long pending_rm_pre_begin;	/* pre-image line of first pending */
-
 	int ret;			/* latched error from orig_line_fn */
 };
 
@@ -2542,26 +2580,48 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
-static void discard_pending_rm(struct line_range_filter *filter)
+/*
+ * Begin a range hunk at the first in-range line.  Its position fixes the
+ * hunk's begins, taken from the two image cursors before they advance:
+ * new_begin from the post-image, old_begin from the pre-image.  The line
+ * counts are not tracked here; flush_range_hunk() derives them from the
+ * buffered lines.
+ */
+static void begin_range_hunk(struct line_range_filter *filter)
 {
-	strbuf_reset(&filter->pending_rm);
-	filter->pending_rm_count = 0;
+	filter->hunk.active = 1;
+	filter->hunk.new_begin = filter->lno_in_postimage;
+	filter->hunk.old_begin = filter->lno_in_preimage;
+	strbuf_reset(&filter->hunk.lines);
 }
 
 static void flush_range_hunk(struct line_range_filter *filter)
 {
 	struct strbuf hdr = STRBUF_INIT;
 	const char *p, *end;
+	long old_count = 0, new_count = 0;
+	int has_changes = 0;
 
 	if (!filter->hunk.active || filter->ret)
 		return;
 
-	/* Drain any pending removal lines into the range hunk */
-	if (filter->pending_rm_count) {
-		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
-		filter->hunk.old_count += filter->pending_rm_count;
-		filter->hunk.has_changes = 1;
-		discard_pending_rm(filter);
+	/*
+	 * Derive the hunk's geometry from the buffered lines: a ' '
+	 * counts on both sides, a '-' on the old side, a '+' on the new.
+	 * A '-' or '+' marks a real change; the "\ No newline at end of
+	 * file" marker (line[0] == '\\') counts on neither side.
+	 */
+	p = filter->hunk.lines.buf;
+	end = p + filter->hunk.lines.len;
+	while (p < end) {
+		const char *eol = memchr(p, '\n', end - p);
+		if (*p == ' ' || *p == '-')
+			old_count++;
+		if (*p == ' ' || *p == '+')
+			new_count++;
+		if (*p == '-' || *p == '+')
+			has_changes = 1;
+		p = eol ? eol + 1 : end;
 	}
 
 	/*
@@ -2570,15 +2630,15 @@ static void flush_range_hunk(struct line_range_filter *filter)
 	 * ctxlen causes xdiff to emit context covering a range that
 	 * has no changes in this commit.
 	 */
-	if (!filter->hunk.has_changes) {
+	if (!has_changes) {
 		filter->hunk.active = 0;
 		strbuf_reset(&filter->hunk.lines);
 		return;
 	}
 
 	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    filter->hunk.old_begin, filter->hunk.old_count,
-		    filter->hunk.new_begin, filter->hunk.new_count);
+		    filter->hunk.old_begin, old_count,
+		    filter->hunk.new_begin, new_count);
 	if (filter->funclen > 0) {
 		strbuf_addch(&hdr, ' ');
 		strbuf_add(&hdr, filter->func, filter->funclen);
@@ -2618,11 +2678,6 @@ static void line_range_hunk_fn(void *data,
 	 * When count > 0, begin is 1-based.  When count == 0, begin is
 	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
 	 * that type will arrive, so the value is unused.
-	 *
-	 * Any pending removal lines from the previous xdiff hunk are
-	 * intentionally left in pending_rm: the line callback will
-	 * flush or discard them when the next content line reveals
-	 * whether the removals precede in-range content.
 	 */
 	filter->lno_in_postimage = new_begin;
 	filter->lno_in_preimage = old_begin;
@@ -2638,88 +2693,56 @@ static void line_range_hunk_fn(void *data,
 static int line_range_line_fn(void *priv, char *line, unsigned long len)
 {
 	struct line_range_filter *filter = priv;
-	const struct range *cur;
-	long idx_in_postimage, cur_pre;
+	long idx_in_postimage;
+	int in_range;
 
 	if (filter->ret)
 		return filter->ret;
 
-	if (line[0] == '-') {
-		if (!filter->pending_rm_count)
-			filter->pending_rm_pre_begin = filter->lno_in_preimage;
-		filter->lno_in_preimage++;
-		strbuf_add(&filter->pending_rm, line, len);
-		filter->pending_rm_count++;
-		return filter->ret;
-	}
-
 	if (line[0] == '\\') {
-		if (filter->pending_rm_count)
-			strbuf_add(&filter->pending_rm, line, len);
-		else if (filter->hunk.active)
+		if (filter->hunk.active)
 			strbuf_add(&filter->hunk.lines, line, len);
-		/* otherwise outside tracked range; drop silently */
 		return filter->ret;
 	}
 
-	if (line[0] != '+' && line[0] != ' ')
+	if (line[0] != '+' && line[0] != ' ' && line[0] != '-')
 		BUG("unexpected diff line type '%c'", line[0]);
 
+	/*
+	 * idx_in_postimage is this line's 0-based post-image index (see the model on
+	 * struct line_range_filter).  The cursors are advanced only after
+	 * the line is classified, so a '-' is tested at the same idx_in_postimage as
+	 * the '+'/' ' that follows it.
+	 */
 	idx_in_postimage = filter->lno_in_postimage - 1;
-	cur_pre = filter->lno_in_preimage;	/* save before advancing for context lines */
-	filter->lno_in_postimage++;
-	if (line[0] == ' ')
-		filter->lno_in_preimage++;
 
-	/* Advance past ranges we've passed */
+	/* Retire ranges we have passed, flushing the one we leave. */
 	while (filter->cur_range < filter->ranges->nr &&
 	       idx_in_postimage >= filter->ranges->ranges[filter->cur_range].end) {
 		if (filter->hunk.active)
 			flush_range_hunk(filter);
-		discard_pending_rm(filter);
 		filter->cur_range++;
 	}
 
-	/* Past all ranges */
-	if (filter->cur_range >= filter->ranges->nr) {
-		discard_pending_rm(filter);
-		return filter->ret;
-	}
+	in_range = filter->cur_range < filter->ranges->nr &&
+		   idx_in_postimage >= filter->ranges->ranges[filter->cur_range].start &&
+		   idx_in_postimage < filter->ranges->ranges[filter->cur_range].end;
 
-	cur = &filter->ranges->ranges[filter->cur_range];
+	if (in_range) {
+		if (!filter->hunk.active)
+			begin_range_hunk(filter);
 
-	/* Before current range */
-	if (idx_in_postimage < cur->start) {
-		discard_pending_rm(filter);
-		return filter->ret;
+		strbuf_add(&filter->hunk.lines, line, len);
 	}
 
-	/* In range so start a new range hunk if needed */
-	if (!filter->hunk.active) {
-		filter->hunk.active = 1;
-		filter->hunk.has_changes = 0;
-		filter->hunk.new_begin = idx_in_postimage + 1;
-		filter->hunk.old_begin = filter->pending_rm_count
-			? filter->pending_rm_pre_begin : cur_pre;
-		filter->hunk.old_count = 0;
-		filter->hunk.new_count = 0;
-		strbuf_reset(&filter->hunk.lines);
-	}
-
-	/* Flush pending removals into range hunk */
-	if (filter->pending_rm_count) {
-		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
-		filter->hunk.old_count += filter->pending_rm_count;
-		filter->hunk.has_changes = 1;
-		discard_pending_rm(filter);
-	}
-
-	strbuf_add(&filter->hunk.lines, line, len);
-	filter->hunk.new_count++;
-	if (line[0] == '+')
-		filter->hunk.has_changes = 1;
-	else
-		filter->hunk.old_count++;
+	/*
+	 * Advance each image's cursor: a line present in that image (see
+	 * the model) consumes one of its line numbers.
+	 */
+	if (line[0] != '-')
+		filter->lno_in_postimage++;
+	if (line[0] != '+')
+		filter->lno_in_preimage++;
 
 	return filter->ret;
 }
@@ -4097,7 +4120,6 @@ static void builtin_diff(const char *name_a,
 			lr_state.orig_cb_data = &ecbdata;
 			lr_state.ranges = line_ranges;
 			strbuf_init(&lr_state.hunk.lines, 0);
-			strbuf_init(&lr_state.pending_rm, 0);
 
 			/*
 			 * Inflate ctxlen so that all changes within
@@ -4132,7 +4154,6 @@ static void builtin_diff(const char *name_a,
 				die("unable to generate diff for %s",
 				    one->path);
 			strbuf_release(&lr_state.hunk.lines);
-			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index ca4eb7bbc7..e9691066de 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -738,6 +738,131 @@ test_expect_success '-L with -G filters to diff-text matches' '
 	grep "F2 + 2" actual
 '
 
+test_expect_success 'setup for trailing deletion test' '
+	git checkout --orphan trailing-del &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 1;
+	}
+	// trailing comment
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "add file with trailing comment" &&
+	# Modify tracked() AND delete the trailing comment in
+	# one commit, so the commit touches the tracked range
+	# and is not filtered out by the revision walker.
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 2;
+	}
+	EOF
+	git commit -a -m "modify tracked and delete trailing comment"
+'
+
+test_expect_success '-L does not include deletions past end of tracked range' '
+	git log -L:tracked:file.c --format= -1 -p >actual &&
+	# The trailing comment deletion is outside the tracked
+	# range and should not appear in the patch output.
+	test_grep "return 2" actual &&
+	test_grep ! "trailing comment" actual
+'
+
+test_expect_success '-L includes leading deletions resolved by in-range line' '
+	git checkout --orphan leading-del &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	// leading comment
+	void tracked()
+	{
+	    return 1;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "add file with leading comment" &&
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 2;
+	}
+	EOF
+	git commit -a -m "modify tracked and delete leading comment" &&
+	git log -L:tracked:file.c --format= -1 -p >actual &&
+	# The leading comment deletion is resolved by the next
+	# non-removal line (void tracked), which is in range: a
+	# removal is classified by the position of the following
+	# line, so it joins the range that line falls in.
+	test_grep "return 2" actual &&
+	test_grep "leading comment" actual
+'
+
+test_expect_success 'setup for line-range filter edge cases' '
+	git checkout --orphan filter-edge &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	void before()
+	{
+	    return 0;
+	}
+
+	void tracked()
+	{
+	    int a = 1;
+	    int b = 2;
+	    int c = 3;
+	    return a + b + c;
+	}
+
+	void after()
+	{
+	    return 9;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "initial"
+'
+
+test_expect_success '-L change at exact first line of range' '
+	git checkout filter-edge &&
+	# Change the function signature (first line of range)
+	sed "s/void tracked/int tracked/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "change first line" &&
+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
+	test_grep "change first line" actual &&
+	test_grep "+int tracked" actual &&
+	test_grep "\\-void tracked" actual
+'
+
+test_expect_success '-L change at exact last line of range' '
+	git checkout filter-edge &&
+	git reset --hard HEAD~1 &&
+	# Change the closing brace line (last line of range)
+	sed "s/^}$/} \/\/ end tracked/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "change last line" &&
+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
+	test_grep "change last line" actual &&
+	test_grep "end tracked" actual
+'
+
+test_expect_success '-L pure deletion in range (no additions)' '
+	git checkout filter-edge &&
+	git reset --hard HEAD~1 &&
+	# Delete a line inside tracked() without adding anything
+	sed "/int c/d" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "pure deletion" &&
+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
+	test_grep "pure deletion" actual &&
+	test_grep "\\-.*int c" actual
+'
+
 test_expect_success '-L with --diff-filter=M excludes root commit' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c --diff-filter=M --format=%s --no-patch >actual &&
-- 
gitgitgadget

[PATCH v2 3/7] diff: emit -L hunk headers via xdiff's formatter

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

The line-range filter builds its own "@@ -<old> +<new> @@" header for
each range hunk.  For a side with no lines (count 0, such as the old
side of a pure insertion), the begin should be the number of the line
before the change, per the convention git diff and xdl_emit_hunk_hdr()
follow.  The hand-rolled code's begin was one too high; in t4211 this
produced

	@@ -25,0 +18,9 @@

an old begin of 25 in a 24-line file, where git diff would give 24.

Stop hand-rolling the header.  flush_range_hunk() now formats it through
xdiff's own emitter: a new xdiff_emit_hunk_header() helper wraps
xdl_emit_hunk_hdr(), the function that produces every other diff's hunk
headers.  The count-0 begin is then correct by construction, and as a
side effect -L headers match git diff exactly, including its omission of
a count of 1 ("@@ -22 +22 @@" rather than "@@ -22,1 +22,1 @@").

xdiff's hunk callback already hands line_range_hunk_fn() a count-0 begin
decremented, so undo that when seeding the cursors and let the formatter
re-apply the convention once, at emit time.

The off-by-one predates this series, and the two regenerated fixtures
reach it from different origins: no-assertion-error has carried it since
its test was added in ab60c693a2 (line-log: fix assertion error,
2025-08-18), while vanishes-early acquired it when 86e986f166 (line-log:
route -L output through the standard diff pipeline) reshaped its tracked
line into a pure insertion.  vanishes-early also drops its count-1
counts.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c                                   | 27 +++++++++++-------------
 t/t4211/sha1/expect.no-assertion-error   |  2 +-
 t/t4211/sha1/expect.vanishes-early       |  6 +++---
 t/t4211/sha256/expect.no-assertion-error |  2 +-
 t/t4211/sha256/expect.vanishes-early     |  6 +++---
 xdiff-interface.c                        | 19 +++++++++++++++++
 xdiff-interface.h                        | 15 +++++++++++++
 7 files changed, 54 insertions(+), 23 deletions(-)

diff --git a/diff.c b/diff.c
index ee765d7ac2..9751bb6798 100644
--- a/diff.c
+++ b/diff.c
@@ -2636,14 +2636,9 @@ static void flush_range_hunk(struct line_range_filter *filter)
 		return;
 	}
 
-	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    filter->hunk.old_begin, old_count,
-		    filter->hunk.new_begin, new_count);
-	if (filter->funclen > 0) {
-		strbuf_addch(&hdr, ' ');
-		strbuf_add(&hdr, filter->func, filter->funclen);
-	}
-	strbuf_addch(&hdr, '\n');
+	xdiff_emit_hunk_header(&hdr, filter->hunk.old_begin, old_count,
+			       filter->hunk.new_begin, new_count,
+			       filter->func, filter->funclen);
 
 	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
@@ -2668,19 +2663,21 @@ static void flush_range_hunk(struct line_range_filter *filter)
 }
 
 static void line_range_hunk_fn(void *data,
-			       long old_begin, long old_nr UNUSED,
-			       long new_begin, long new_nr UNUSED,
+			       long old_begin, long old_nr,
+			       long new_begin, long new_nr,
 			       const char *func, long funclen)
 {
 	struct line_range_filter *filter = data;
 
 	/*
-	 * When count > 0, begin is 1-based.  When count == 0, begin is
-	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
-	 * that type will arrive, so the value is unused.
+	 * Seed the per-image line cursors from the hunk header's begins.  For
+	 * a side with no lines (count 0), xdiff's callback has already moved
+	 * its begin to the line before the change, so add one back to recover
+	 * the true 1-based start.  xdiff_emit_hunk_header() reapplies that -1
+	 * when the clipped hunk is emitted.
 	 */
-	filter->lno_in_postimage = new_begin;
-	filter->lno_in_preimage = old_begin;
+	filter->lno_in_postimage = new_nr ? new_begin : new_begin + 1;
+	filter->lno_in_preimage = old_nr ? old_begin : old_begin + 1;
 
 	if (funclen > 0) {
 		if (funclen > (long)sizeof(filter->func))
diff --git a/t/t4211/sha1/expect.no-assertion-error b/t/t4211/sha1/expect.no-assertion-error
index 54c568f273..95faf51a7b 100644
--- a/t/t4211/sha1/expect.no-assertion-error
+++ b/t/t4211/sha1/expect.no-assertion-error
@@ -8,7 +8,7 @@ diff --git a/b.c b/b.c
 index bf79c2f..27c829c 100644
 --- a/b.c
 +++ b/b.c
-@@ -25,0 +18,9 @@
+@@ -24,0 +18,9 @@
 +long f(long x)
 +{
 +	int s = 0;
diff --git a/t/t4211/sha1/expect.vanishes-early b/t/t4211/sha1/expect.vanishes-early
index a413ad3659..e4b1a201d5 100644
--- a/t/t4211/sha1/expect.vanishes-early
+++ b/t/t4211/sha1/expect.vanishes-early
@@ -8,7 +8,7 @@ diff --git a/a.c b/a.c
 index 0b9cae5..5de3ea4 100644
 --- a/a.c
 +++ b/a.c
-@@ -23,0 +24,1 @@ int main ()
+@@ -22,0 +24 @@ int main ()
 +/* incomplete lines are bad! */
 
 commit 100b61a6f2f720f812620a9d10afb3a960ccb73c
@@ -21,7 +21,7 @@ diff --git a/a.c b/a.c
 index 5e709a1..0b9cae5 100644
 --- a/a.c
 +++ b/a.c
-@@ -22,1 +22,1 @@ int main ()
+@@ -22 +22 @@ int main ()
 -}
 +}
 \ No newline at end of file
@@ -37,5 +37,5 @@ new file mode 100644
 index 0000000..444e415
 --- /dev/null
 +++ b/a.c
-@@ -0,0 +20,1 @@
+@@ -0,0 +20 @@
 +}
diff --git a/t/t4211/sha256/expect.no-assertion-error b/t/t4211/sha256/expect.no-assertion-error
index c25f2ce19c..815d27f7f1 100644
--- a/t/t4211/sha256/expect.no-assertion-error
+++ b/t/t4211/sha256/expect.no-assertion-error
@@ -8,7 +8,7 @@ diff --git a/b.c b/b.c
 index 69cb69c..a0d566e 100644
 --- a/b.c
 +++ b/b.c
-@@ -25,0 +18,9 @@
+@@ -24,0 +18,9 @@
 +long f(long x)
 +{
 +	int s = 0;
diff --git a/t/t4211/sha256/expect.vanishes-early b/t/t4211/sha256/expect.vanishes-early
index bc33b963dc..263fc9eaac 100644
--- a/t/t4211/sha256/expect.vanishes-early
+++ b/t/t4211/sha256/expect.vanishes-early
@@ -8,7 +8,7 @@ diff --git a/a.c b/a.c
 index e4fa1d8..62c1fc2 100644
 --- a/a.c
 +++ b/a.c
-@@ -23,0 +24,1 @@ int main ()
+@@ -22,0 +24 @@ int main ()
 +/* incomplete lines are bad! */
 
 commit 29f32ac3141c48b22803e5c4127b719917b67d0f8ca8c5248bebfa2a19f7da10
@@ -21,7 +21,7 @@ diff --git a/a.c b/a.c
 index d325124..e4fa1d8 100644
 --- a/a.c
 +++ b/a.c
-@@ -22,1 +22,1 @@ int main ()
+@@ -22 +22 @@ int main ()
 -}
 +}
 \ No newline at end of file
@@ -37,5 +37,5 @@ new file mode 100644
 index 0000000..9f550c3
 --- /dev/null
 +++ b/a.c
-@@ -0,0 +20,1 @@
+@@ -0,0 +20 @@
 +}
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 5ee2b96d0a..32e04630ee 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -91,6 +91,25 @@ static int xdiff_outf(void *priv_, mmbuffer_t *mb, int nbuf)
 	return 0;
 }
 
+static int strbuf_out_line(void *priv, mmbuffer_t *mb, int nbuf)
+{
+	struct strbuf *out = priv;
+	int i;
+	for (i = 0; i < nbuf; i++)
+		strbuf_add(out, mb[i].ptr, mb[i].size);
+	return 0;
+}
+
+void xdiff_emit_hunk_header(struct strbuf *out,
+			    long old_begin, long old_count,
+			    long new_begin, long new_count,
+			    const char *func, long funclen)
+{
+	xdemitcb_t ecb = { .priv = out, .out_line = strbuf_out_line };
+	xdl_emit_hunk_hdr(old_begin, old_count, new_begin, new_count,
+			  func, funclen, &ecb);
+}
+
 /*
  * Trim down common substring at the end of the buffers,
  * but end on a complete line.
diff --git a/xdiff-interface.h b/xdiff-interface.h
index ce54e1c0e0..51c88296ed 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -76,4 +76,19 @@ int xdiff_compare_lines(const char *l1, long s1,
  */
 unsigned long xdiff_hash_string(const char *s, size_t len, long flags);
 
+struct strbuf;
+
+/*
+ * Append a unified-diff hunk header to `out`, e.g.
+ * "@@ -<old> +<new> @@ func\n".  The header comes from wrapping xdiff's
+ * own hunk-header emitter, so it matches what a normal diff would
+ * produce for these begins and counts.  For a side with no lines
+ * (count 0) the begin is the line before the change, and a count of 1
+ * is omitted.
+ */
+void xdiff_emit_hunk_header(struct strbuf *out,
+			    long old_begin, long old_count,
+			    long new_begin, long new_count,
+			    const char *func, long funclen);
+
 #endif
-- 
gitgitgadget

[PATCH v2 4/7] diff: extract a line-range diff helper for reuse

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

builtin_diff() open-codes the line-range filter setup and teardown
around its xdi_diff_outf() call: zero the struct, point it at the
output callback, inflate ctxlen to the largest range span so each range
yields a single xdiff hunk, run the diff, flush the trailing range
hunk, and release the buffer.  The upcoming -L stat and check formats
need the same sequence.

Extract line_range_filter_init() for the setup and a
line_range_filter_diff() helper that prepares the xdiff config the
filter needs, runs an initialized filter through xdi_diff_outf(),
flushes the final range hunk, and releases it, returning the latched
error.  The helper inflates ctxlen to the largest range span so each
range yields a single xdiff hunk, and clears XDL_EMIT_NO_HUNK_HDR so
the hunk headers the filter seeds its position from are always emitted.
Folding both into the helper keeps these invariants, which the filter's
position tracking relies on, in a single place for every consumer.
builtin_diff() now does init + line_range_filter_diff(); the next two
patches reuse them in builtin_diffstat() and builtin_checkdiff()
instead of repeating the boilerplate.

No behavior change: builtin_diff() leaves XDL_EMIT_NO_HUNK_HDR unset,
so clearing it is a no-op until the suppressing consumers arrive.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c | 100 +++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 61 insertions(+), 39 deletions(-)

diff --git a/diff.c b/diff.c
index 9751bb6798..6233a96bf0 100644
--- a/diff.c
+++ b/diff.c
@@ -2580,6 +2580,18 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
+static void line_range_filter_init(struct line_range_filter *filter,
+				   const struct range_set *ranges,
+				   xdiff_emit_line_fn line_fn,
+				   void *cb_data)
+{
+	memset(filter, 0, sizeof(*filter));
+	filter->orig_line_fn = line_fn;
+	filter->orig_cb_data = cb_data;
+	filter->ranges = ranges;
+	strbuf_init(&filter->hunk.lines, 0);
+}
+
 /*
  * Begin a range hunk at the first in-range line.  Its position fixes the
  * hunk's begins, taken from the two image cursors before they advance:
@@ -2744,6 +2756,50 @@ static int line_range_line_fn(void *priv, char *line, unsigned long len)
 	return filter->ret;
 }
 
+/*
+ * Run an xdiff pass through an initialized line-range filter, flush the
+ * final range hunk, and release the filter.  Inflates ctxlen to the largest
+ * range span first, so that every change within a single range lands in one
+ * xdiff hunk and the inter-change context is emitted; the filter then clips
+ * back to range boundaries.  The optimal ctxlen depends on where changes fall
+ * within the range, which is only known after xdiff runs, so the max span is
+ * the upper bound that guarantees correctness in a single pass.  Every
+ * consumer (patch, diffstat, check) relies on one xdiff hunk per range, so
+ * this lives here rather than at each call site.  Also clears
+ * XDL_EMIT_NO_HUNK_HDR: the filter seeds its per-image position from the hunk
+ * headers, so a consumer that otherwise suppresses them (diffstat) still gets
+ * them here.  Returns non-zero if xdiff or any forwarded callback failed.
+ */
+static int line_range_filter_diff(struct line_range_filter *filter,
+				  mmfile_t *mf1, mmfile_t *mf2,
+				  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	const struct range_set *ranges = filter->ranges;
+	long max_span = 0;
+	unsigned int i;
+	int ret;
+
+	for (i = 0; i < ranges->nr; i++) {
+		long span = ranges->ranges[i].end - ranges->ranges[i].start;
+		if (span > max_span)
+			max_span = span;
+	}
+	if (max_span > xecfg->ctxlen)
+		xecfg->ctxlen = max_span;
+
+	/* the filter seeds its per-image position from hunk headers */
+	xecfg->flags &= ~XDL_EMIT_NO_HUNK_HDR;
+
+	ret = xdi_diff_outf(mf1, mf2, line_range_hunk_fn,
+			    line_range_line_fn, filter, xpp, xecfg);
+	if (!ret) {
+		flush_range_hunk(filter);
+		ret = filter->ret;
+	}
+	strbuf_release(&filter->hunk.lines);
+	return ret;
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
@@ -4108,49 +4164,15 @@ static void builtin_diff(const char *name_a,
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
 		} else if (line_ranges) {
-			struct line_range_filter lr_state;
-			unsigned int i;
-			long max_span = 0;
+			struct line_range_filter lr_filter;
 
-			memset(&lr_state, 0, sizeof(lr_state));
-			lr_state.orig_line_fn = fn_out_consume;
-			lr_state.orig_cb_data = &ecbdata;
-			lr_state.ranges = line_ranges;
-			strbuf_init(&lr_state.hunk.lines, 0);
-
-			/*
-			 * Inflate ctxlen so that all changes within
-			 * any single range are merged into one xdiff
-			 * hunk and the inter-change context is emitted.
-			 * The callback clips back to range boundaries.
-			 *
-			 * The optimal ctxlen depends on where changes
-			 * fall within the range, which is only known
-			 * after xdiff runs; the max range span is the
-			 * upper bound that guarantees correctness in a
-			 * single pass.
-			 */
-			for (i = 0; i < line_ranges->nr; i++) {
-				long span = line_ranges->ranges[i].end -
-					    line_ranges->ranges[i].start;
-				if (span > max_span)
-					max_span = span;
-			}
-			if (max_span > xecfg.ctxlen)
-				xecfg.ctxlen = max_span;
-
-			if (xdi_diff_outf(&mf1, &mf2,
-					  line_range_hunk_fn,
-					  line_range_line_fn,
-					  &lr_state, &xpp, &xecfg))
-				die("unable to generate diff for %s",
-				    one->path);
+			line_range_filter_init(&lr_filter, line_ranges,
+					       fn_out_consume, &ecbdata);
 
-			flush_range_hunk(&lr_state);
-			if (lr_state.ret)
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
 				die("unable to generate diff for %s",
 				    one->path);
-			strbuf_release(&lr_state.hunk.lines);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
-- 
gitgitgadget

[PATCH v2 5/7] line-log: support diff stat formats with -L

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Reuse the line_range_filter in builtin_diffstat() so the stat formats
count only the lines within the tracked range.  When a filepair carries
line_ranges, the filter wraps diffstat_consume() as its output callback,
forwarding only the lines inside the range for counting.
flush_range_hunk() replays buffered content through diffstat_consume(),
which ignores synthetic @@ headers since it only counts '+' and '-'
lines.

Expand the output format allowlist in setup_revisions() to accept
--stat, --numstat, and --shortstat with -L.

Leave --dirstat out of the allowlist so it is rejected like any other
unsupported format.  Its default mode counts each file's whole-file
byte damage via diffcore_count_changes(), outside the line-based
pipeline that the -L filter scopes, so bare --dirstat cannot honor the
tracked range.  The --dirstat=lines mode could: it aggregates the same
per-file line counts as --numstat, which -L already scopes.  But
accepting only that sub-mode while bare --dirstat keeps erroring is a
confusing split, so the whole format is deferred to a follow-up;
--numstat already reports the exact per-file counts within the tracked
range.

Also drop "yet" from the generic -L rejection message ("does not
yet support the requested diff format").  Some rejected formats do
not fit a line range at all, so "yet" wrongly implied they are all
just awaiting support.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  12 ++-
 diff.c                                |  13 ++-
 revision.c                            |   6 +-
 t/t4211-line-log.sh                   | 150 ++++++++++++++++++++++----
 4 files changed, 155 insertions(+), 26 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index 72f639b5e7..a111a492b4 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -9,10 +9,14 @@
 	_<start>_ and _<end>_ (or _<funcname>_) must exist in the starting revision.
 	You can specify this option more than once. Implies `--patch`.
 	Patch output can be suppressed using `--no-patch`.
-	Non-patch diff formats `--raw`, `--name-only`, `--name-status`,
-	and `--summary` are supported.  Diff stat formats
-	(`--stat`, `--numstat`, `--shortstat`, `--dirstat`) are not
-	currently implemented.
+	The following non-patch diff formats are supported: `--raw`,
+	`--name-only`, `--name-status`, `--summary`,
+	`--stat`, `--numstat`, and `--shortstat`.
+	The stat formats count only lines within the tracked range.
+	`--dirstat` is not supported
+	with `-L`: it summarizes change as each directory's share of
+	the total churn, not as counts for the tracked lines.  Use
+	`--numstat` for exact per-file counts within the range.
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
diff --git a/diff.c b/diff.c
index 6233a96bf0..026fafeb90 100644
--- a/diff.c
+++ b/diff.c
@@ -4289,7 +4289,18 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 		xecfg.ctxlen = o->context;
 		xecfg.interhunkctxlen = o->interhunkcontext;
 		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
-		if (xdi_diff_outf(&mf1, &mf2, NULL,
+
+		if (p->line_ranges) {
+			struct line_range_filter lr_filter;
+
+			line_range_filter_init(&lr_filter, p->line_ranges,
+					       diffstat_consume, diffstat);
+
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
+				die("unable to generate diffstat for %s",
+				    one->path);
+		} else if (xdi_diff_outf(&mf1, &mf2, NULL,
 				  diffstat_consume, diffstat, &xpp, &xecfg))
 			die("unable to generate diffstat for %s", one->path);
 
diff --git a/revision.c b/revision.c
index 6a8101e8b7..2c76e15778 100644
--- a/revision.c
+++ b/revision.c
@@ -3193,8 +3193,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 	     (revs->diffopt.output_format &
 	      ~(DIFF_FORMAT_PATCH | DIFF_FORMAT_NO_OUTPUT |
 		DIFF_FORMAT_RAW | DIFF_FORMAT_NAME |
-		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY))))
-		die(_("-L does not yet support the requested diff format"));
+		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY |
+		DIFF_FORMAT_NUMSTAT | DIFF_FORMAT_DIFFSTAT |
+		DIFF_FORMAT_SHORTSTAT))))
+		die(_("-L does not support the requested diff format"));
 
 	if (revs->expand_tabs_in_log < 0)
 		revs->expand_tabs_in_log = revs->expand_tabs_in_log_default;
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index e9691066de..b9ca336dbc 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -176,24 +176,15 @@ test_expect_success '--name-status shows status and path' '
 	test_grep ! "^@@" actual
 '
 
-test_expect_success '--stat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --stat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--numstat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --numstat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--shortstat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --shortstat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--dirstat is not yet supported with -L' '
+test_expect_success '--dirstat is not supported with -L' '
+	# --dirstat is not supported with -L: its default mode measures
+	# whole-file change, not the tracked lines, and the
+	# --dirstat=lines variant is deferred too, so both forms are
+	# rejected like any other unsupported format.
 	test_must_fail git log -L1,24:b.c --dirstat 2>err &&
-	test_grep "does not yet support" err
+	test_grep "does not support" err &&
+	test_must_fail git log -L1,24:b.c --dirstat=lines 2>err &&
+	test_grep "does not support" err
 '
 
 test_expect_success 'setup for checking fancy rename following' '
@@ -887,9 +878,9 @@ test_expect_success '-L with -S suppresses non-matching commits' '
 	test_cmp expect actual
 '
 
-test_expect_success '--full-diff is not yet supported with -L' '
+test_expect_success '--full-diff is not supported with -L' '
 	test_must_fail git log -L1,24:b.c --full-diff 2>err &&
-	test_grep "does not yet support" err
+	test_grep "does not support" err
 '
 
 test_expect_success '-L --oneline has no extra blank line before diff' '
@@ -900,6 +891,127 @@ test_expect_success '-L --oneline has no extra blank line before diff' '
 	test_grep "^diff --git" line2
 '
 
+test_expect_success 'setup for stat range-scoping tests' '
+	git checkout --orphan stat-scoping &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "Add func1() and func2()" &&
+
+	# Modify both functions in a single commit so that
+	# whole-file stats differ from the counts for the tracked range.
+	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "Modify both functions"
+'
+
+test_expect_success '--numstat counts only lines in tracked range' '
+	# "Modify both functions" changes one line in func1 and one in
+	# func2.  Whole-file numstat would show 2 added, 2 deleted.
+	# numstat for func2 within the tracked range should show only 1 and 1.
+	git log -L:func2:file.c --numstat --format=%s -1 >actual &&
+	test_grep "Modify both functions" actual &&
+	test_grep "^1	1	file.c$" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--numstat counts only additions for root commit' '
+	# Root commit creates both func1 (4 lines) and func2 (4 lines).
+	# Whole-file numstat would show 9 lines added.  numstat for func2
+	# within the tracked range should show only 4.
+	git log -L:func2:file.c --numstat --format=%s >actual &&
+	test_grep "Add func1() and func2()" actual &&
+	test_grep "^4	0	file.c$" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--stat counts only lines in tracked range' '
+	git log -L:func2:file.c --stat --format=%s -1 >actual &&
+	test_grep "Modify both functions" actual &&
+	test_grep "file.c |" actual &&
+	test_grep "1 insertion" actual &&
+	test_grep "1 deletion" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--shortstat counts only lines in tracked range' '
+	# --shortstat prints only the summary line: no per-file "file.c |"
+	# line.  Counts cover only the tracked range, as for --numstat above.
+	git log -L:func2:file.c --shortstat --format=%s -1 >actual &&
+	test_grep "Modify both functions" actual &&
+	test_grep "1 insertion" actual &&
+	test_grep "1 deletion" actual &&
+	test_grep ! "file.c |" actual &&
+	test_grep ! "^diff --git" actual
+'
+
+test_expect_success '--numstat across renames and multiple commits' '
+	# parallel-change carries the tracked function f across an a.c -> b.c
+	# rename and a merge of two parallel histories.  With -M, --numstat
+	# follows the rename and reports added/removed counts for f within
+	# the tracked range (not whole-file) per commit; the file column flips from
+	# b.c to a.c at the rename as the walk goes back in time.  Commits
+	# that do not change the range of f emit no row (the merge and the
+	# pure file-move produce nothing), so there are fewer rows than
+	# commits.
+	git checkout parallel-change &&
+	git log -M -L ":f:b.c" --format= --numstat >actual &&
+	cat >expect <<-\EOF &&
+	1	1	b.c
+	1	1	a.c
+	1	1	a.c
+	1	1	a.c
+	1	0	a.c
+	13	0	a.c
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '-L multiple ranges with --numstat excludes untracked change' '
+	git checkout --orphan multi-range &&
+	git reset --hard &&
+	cat >m.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+
+	int func3()
+	{
+	    return F3;
+	}
+	EOF
+	git add m.c &&
+	test_tick &&
+	git commit -m "add m.c" &&
+	# Change all three functions but track only func1 and func2.
+	# Whole-file numstat would be 3 3; a 2 2 result proves the
+	# untracked func3 change is excluded and the two ranges just sum.
+	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" -e "s/F3/F3 + 3/" m.c >tmp &&
+	mv tmp m.c &&
+	git commit -a -m "Modify all three functions" &&
+	git log -L:func1:m.c -L:func2:m.c --numstat --format=%s -1 >actual &&
+	test_grep "Modify all three functions" actual &&
+	test_grep "^2	2	m.c$" actual &&
+	test_grep ! "^3	3	m.c$" actual
+'
+
 test_expect_success '--summary shows new file on root commit' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c --summary --format= >actual &&
-- 
gitgitgadget

[PATCH v2 6/7] diff: support --check with -L line ranges

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

builtin_checkdiff() runs its own xdiff pass to detect whitespace
errors in newly added lines.  When -L is active, the check should
be scoped to the tracked line ranges rather than the whole file.

Reuse the line_range_filter to wrap checkdiff_consume(), the same
pattern already used for patch output and diffstat.  The filter
forwards only in-range lines for whitespace checking.

checkdiff reports the file line number of each error, which it
normally learns from the hunk header via checkdiff_consume_hunk().
The filter synthesizes its own hunk headers, so give it an optional
hunk callback and route checkdiff_consume_hunk() through it; this
sets the post-image position before the in-range lines are replayed.
Without it the reported line numbers would count from the start of
the range hunk rather than the start of the file.

The trailing blank-at-eof check is a second pass that scans the whole
file via check_blank_at_eof(), so gate its report on the tracked
ranges as well; otherwise a blank line added at end of file is
reported even when it lies outside the range.

Add DIFF_FORMAT_CHECKDIFF to the -L output format allowlist in
setup_revisions() so that -L --check is accepted, and list --check
among the supported formats in the documentation.  Add tests covering
that whitespace errors are reported, scoped to the tracked range, and
labeled with the correct file line number, including when two errors
in one range are separated by a gap that would otherwise split into
multiple xdiff hunks.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  2 +-
 diff.c                                | 65 ++++++++++++++++++-
 revision.c                            |  2 +-
 t/t4211-line-log.sh                   | 92 +++++++++++++++++++++++++++
 4 files changed, 156 insertions(+), 5 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index a111a492b4..33b4e94881 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -10,7 +10,7 @@
 	You can specify this option more than once. Implies `--patch`.
 	Patch output can be suppressed using `--no-patch`.
 	The following non-patch diff formats are supported: `--raw`,
-	`--name-only`, `--name-status`, `--summary`,
+	`--name-only`, `--name-status`, `--summary`, `--check`,
 	`--stat`, `--numstat`, and `--shortstat`.
 	The stat formats count only lines within the tracked range.
 	`--dirstat` is not supported
diff --git a/diff.c b/diff.c
index 026fafeb90..519c513356 100644
--- a/diff.c
+++ b/diff.c
@@ -665,6 +665,12 @@ struct emit_callback {
  */
 struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
+	/*
+	 * Optional; consumers that report file line numbers (e.g.
+	 * checkdiff) need the synthetic hunk header to set their
+	 * post-image position before in-range lines are replayed.
+	 */
+	xdiff_emit_hunk_fn orig_hunk_fn;
 	void *orig_cb_data;
 	const struct range_set *ranges;	/* 0-based [start, end) */
 	unsigned int cur_range;		/* index into the range_set */
@@ -2652,6 +2658,17 @@ static void flush_range_hunk(struct line_range_filter *filter)
 			       filter->hunk.new_begin, new_count,
 			       filter->func, filter->funclen);
 
+	/*
+	 * Inform a line-numbering consumer of the post-image position
+	 * before replaying lines, mirroring the hunk callback xdiff
+	 * would have issued for a non-scoped diff.
+	 */
+	if (filter->orig_hunk_fn)
+		filter->orig_hunk_fn(filter->orig_cb_data,
+				filter->hunk.old_begin, old_count,
+				filter->hunk.new_begin, new_count,
+				filter->func, filter->funclen);
+
 	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
 
@@ -4330,11 +4347,29 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 	diff_free_filespec_data(two);
 }
 
+/*
+ * Is the 0-based line index within any of the tracked ranges?
+ * (range_set ranges are 0-based, half-open [start, end).)  This is a
+ * one-shot query for a single line and scans; the streaming filter
+ * (line_range_line_fn) uses a forward cursor instead.
+ */
+static int idx_in_ranges(const struct range_set *ranges, long idx)
+{
+	unsigned int i;
+
+	for (i = 0; i < ranges->nr; i++)
+		if (idx >= ranges->ranges[i].start &&
+		    idx < ranges->ranges[i].end)
+			return 1;
+	return 0;
+}
+
 static void builtin_checkdiff(const char *name_a, const char *name_b,
 			      const char *attr_path,
 			      struct diff_filespec *one,
 			      struct diff_filespec *two,
-			      struct diff_options *o)
+			      struct diff_options *o,
+			      const struct range_set *line_ranges)
 {
 	mmfile_t mf1, mf2;
 	struct checkdiff_t data;
@@ -4374,7 +4409,19 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 		memset(&xecfg, 0, sizeof(xecfg));
 		xecfg.ctxlen = 1; /* at least one context line */
 		xpp.flags = 0;
-		if (xdi_diff_outf(&mf1, &mf2, checkdiff_consume_hunk,
+
+		if (line_ranges) {
+			struct line_range_filter lr_filter;
+
+			line_range_filter_init(&lr_filter, line_ranges,
+					       checkdiff_consume, &data);
+			lr_filter.orig_hunk_fn = checkdiff_consume_hunk;
+
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
+				die("unable to generate checkdiff for %s",
+				    one->path);
+		} else if (xdi_diff_outf(&mf1, &mf2, checkdiff_consume_hunk,
 				  checkdiff_consume, &data,
 				  &xpp, &xecfg))
 			die("unable to generate checkdiff for %s", one->path);
@@ -4387,6 +4434,17 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 			check_blank_at_eof(&mf1, &mf2, &ecbdata);
 			blank_at_eof = ecbdata.blank_at_eof_in_postimage;
 
+			/*
+			 * check_blank_at_eof() scans the whole file; with -L,
+			 * keep the report only when its line is in a tracked
+			 * range.  The error's location is the first trailing
+			 * blank line (blank_at_eof, 1-based; ranges 0-based), so
+			 * we scope by that line.
+			 */
+			if (blank_at_eof && line_ranges &&
+			    !idx_in_ranges(line_ranges, blank_at_eof - 1))
+				blank_at_eof = 0;
+
 			if (blank_at_eof) {
 				static char *err;
 				if (!err)
@@ -5179,7 +5237,8 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 	diff_fill_oid_info(p->one, o->repo->index);
 	diff_fill_oid_info(p->two, o->repo->index);
 
-	builtin_checkdiff(name, other, attr_path, p->one, p->two, o);
+	builtin_checkdiff(name, other, attr_path, p->one, p->two, o,
+			  p->line_ranges);
 }
 
 void repo_diff_setup(struct repository *r, struct diff_options *options)
diff --git a/revision.c b/revision.c
index 2c76e15778..7abb287451 100644
--- a/revision.c
+++ b/revision.c
@@ -3195,7 +3195,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 		DIFF_FORMAT_RAW | DIFF_FORMAT_NAME |
 		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY |
 		DIFF_FORMAT_NUMSTAT | DIFF_FORMAT_DIFFSTAT |
-		DIFF_FORMAT_SHORTSTAT))))
+		DIFF_FORMAT_SHORTSTAT | DIFF_FORMAT_CHECKDIFF))))
 		die(_("-L does not support the requested diff format"));
 
 	if (revs->expand_tabs_in_log < 0)
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index b9ca336dbc..68576418f4 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -1018,4 +1018,96 @@ test_expect_success '--summary shows new file on root commit' '
 	test_grep "create mode 100644 file.c" actual
 '
 
+test_expect_success 'setup for --check test' '
+	git checkout --orphan check-test &&
+	git reset --hard &&
+	cat >check.c <<-\EOF &&
+	void tracked()
+	{
+	    return;
+	}
+
+	void other()
+	{
+	    return;
+	}
+	EOF
+	git add check.c &&
+	test_tick &&
+	git commit -m "add check.c" &&
+	# Introduce trailing whitespace errors in both functions
+	sed "s/return;/return; /" check.c >check.c.tmp &&
+	mv check.c.tmp check.c &&
+	git commit -a -m "introduce trailing whitespace"
+'
+
+test_expect_success '--check scoped to tracked range with correct file line' '
+	# tracked() trailing whitespace is at check.c:3; report it with the
+	# real file line number, not a count from the start of the range
+	# hunk.  other() at check.c:8 is outside the range and is excluded.
+	test_must_fail git log -L:tracked:check.c --check --format= >actual &&
+	test_grep "check.c:3: trailing whitespace" actual &&
+	test_grep ! "check.c:8:" actual
+'
+
+test_expect_success '--check reports each of several tracked ranges' '
+	# Track both functions as separate ranges.  Each range is flushed
+	# as its own hunk, so the second error must report its real file
+	# line (check.c:8), not continue the numbering from the first
+	# range (check.c:3).
+	test_must_fail git log -L:tracked:check.c -L:other:check.c \
+		--check --format= >actual &&
+	test_grep "check.c:3: trailing whitespace" actual &&
+	test_grep "check.c:8: trailing whitespace" actual
+'
+
+test_expect_success '--check line numbers stay correct across a gap in one range' '
+	git checkout --orphan check-gap &&
+	git reset --hard &&
+	cat >gap.c <<-\EOF &&
+	void tracked()
+	{
+	    int a = 1;
+	    int b = 2;
+	    int c = 3;
+	    int d = 4;
+	    int e = 5;
+	    int g = 7;
+	    return;
+	}
+	EOF
+	git add gap.c &&
+	test_tick &&
+	git commit -m "add gap.c" &&
+	# Two trailing-whitespace errors within one tracked range,
+	# separated by clean lines.  ctxlen is inflated to the range span,
+	# so they land in a single xdiff hunk with the gap as context;
+	# both must report their real file line number, with the context
+	# lines between them counted.
+	sed -e "s/int a = 1;/int a = 1; /" -e "s/int g = 7;/int g = 7; /" gap.c >tmp &&
+	mv tmp gap.c &&
+	git commit -a -m "ws errors with a gap" &&
+	test_must_fail git log -L:tracked:gap.c --check --format= >actual &&
+	test_grep "gap.c:3: trailing whitespace" actual &&
+	test_grep "gap.c:8: trailing whitespace" actual
+'
+
+test_expect_success '--check does not report blank-at-eof outside the range' '
+	git checkout --orphan check-eof &&
+	git reset --hard &&
+	printf "void tracked()\n{\n    return;\n}\n\nint tail = 1;\n" >eof.c &&
+	git add eof.c &&
+	test_tick &&
+	git commit -m "add eof.c" &&
+	# One commit introduces a trailing-whitespace error inside tracked()
+	# (line 3) and a blank line at end of file (line 7, outside the
+	# range).  The blank-at-eof check scans the whole file, so it must be
+	# scoped: report the in-range error, not the out-of-range EOF blank.
+	printf "void tracked()\n{\n    return; \n}\n\nint tail = 1;\n\n" >eof.c &&
+	git commit -a -m "ws in range, blank at eof out of range" &&
+	test_must_fail git log -L:tracked:eof.c --check --format= >actual &&
+	test_grep "eof.c:3: trailing whitespace" actual &&
+	test_grep ! "blank line at EOF" actual
+'
+
 test_done
-- 
gitgitgadget

[PATCH v2 7/7] diffcore-pickaxe: scope -G to the -L tracked range

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

git log -L scopes its diff output to the tracked range, but pickaxe
(-S, -G) still runs in diffcore over the whole-file change, so -L -G
selects a commit whenever the pattern appears in any added or removed
line of the file, even outside the tracked range.

Teach -G to honor the range.  diff_grep() already runs an xdiff pass
and greps the +/- lines; route that pass through the line-range filter
so only the tracked range's lines are grepped.  Expose the filter as
diff_emit_line_ranges(), an xdi_diff_outf() that emits only the tracked
range's lines, thread the filepair's line_ranges through the pickaxe
callback, and pass it from pickaxe_match().  Skip scoping under
textconv, whose output is not in the original file's line coordinates.

-G needs only a hit/no-hit answer, so the line-number concerns the
filter handles for patch and check output do not apply here.

-S is left matching the whole file: it counts needle occurrences per
blob rather than grepping the diff, so scoping it needs a different
approach, left to a follow-up.  has_changes() takes the range parameter
but ignores it for now.

Document the resulting -L pickaxe scoping: -G is scoped to the tracked
range, while -S still matches the whole file.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  5 +-
 diff.c                                | 15 ++++++
 diffcore-pickaxe.c                    | 37 +++++++++++---
 t/t4211-line-log.sh                   | 72 +++++++++++++++++++++++++--
 xdiff-interface.h                     | 13 +++++
 5 files changed, 130 insertions(+), 12 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index 33b4e94881..d619ffa633 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -20,6 +20,9 @@
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
-as are pickaxe options (`-S`, `-G`) and `--diff-filter`.
+as are pickaxe options (`-S`, `-G`) and `--diff-filter`.  `-G` is
+scoped to the tracked range; `-S` is still evaluated over the whole
+file, so an `-S` query may select a commit for a change outside the
+range.
 +
 include::line-range-format.adoc[]
diff --git a/diff.c b/diff.c
index 519c513356..a8f346621b 100644
--- a/diff.c
+++ b/diff.c
@@ -2817,6 +2817,21 @@ static int line_range_filter_diff(struct line_range_filter *filter,
 	return ret;
 }
 
+/*
+ * Expose the in-file line-range filter to callers outside diff.c (e.g.
+ * pickaxe -G); see xdiff-interface.h for the contract.
+ */
+int diff_emit_line_ranges(mmfile_t *one, mmfile_t *two,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	struct line_range_filter filter;
+
+	line_range_filter_init(&filter, ranges, line_fn, cb_data);
+	return line_range_filter_diff(&filter, one, two, xpp, xecfg);
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index a52d569911..047b2bf7ac 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -16,7 +16,8 @@
 
 typedef int (*pickaxe_fn)(mmfile_t *one, mmfile_t *two,
 			  struct diff_options *o,
-			  regex_t *regexp, kwset_t kws);
+			  regex_t *regexp, kwset_t kws,
+			  const struct range_set *ranges);
 
 struct diffgrep_cb {
 	regex_t *regexp;
@@ -42,7 +43,8 @@ static int diffgrep_consume(void *priv, char *line, unsigned long len)
 
 static int diff_grep(mmfile_t *one, mmfile_t *two,
 		     struct diff_options *o,
-		     regex_t *regexp, kwset_t kws UNUSED)
+		     regex_t *regexp, kwset_t kws UNUSED,
+		     const struct range_set *ranges)
 {
 	struct diffgrep_cb ecbdata;
 	xpparam_t xpp;
@@ -50,8 +52,11 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	int ret;
 
 	/*
-	 * We have both sides; need to run textual diff and see if
-	 * the pattern appears on added/deleted lines.
+	 * We have both sides; need to run textual diff and see if the
+	 * pattern appears on added/deleted lines.  Under -L (ranges set),
+	 * forward only the tracked range's lines so the match is scoped.
+	 * -G needs only a hit/no-hit answer, so the line-number bookkeeping
+	 * the filter does for -L patch and check output is irrelevant here.
 	 */
 	memset(&xpp, 0, sizeof(xpp));
 	memset(&xecfg, 0, sizeof(xecfg));
@@ -65,8 +70,12 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	 * An xdiff error might be our "data->hit" from above. See the
 	 * comment for xdiff_emit_line_fn in xdiff-interface.h
 	 */
-	ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
-			    &ecbdata, &xpp, &xecfg);
+	if (ranges)
+		ret = diff_emit_line_ranges(one, two, ranges, diffgrep_consume,
+					    &ecbdata, &xpp, &xecfg);
+	else
+		ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
+				    &ecbdata, &xpp, &xecfg);
 	if (ecbdata.hit)
 		return 1;
 	if (ret)
@@ -119,8 +128,13 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws,
 
 static int has_changes(mmfile_t *one, mmfile_t *two,
 		       struct diff_options *o UNUSED,
-		       regex_t *regexp, kwset_t kws)
+		       regex_t *regexp, kwset_t kws,
+		       const struct range_set *ranges UNUSED)
 {
+	/*
+	 * -S counts needle occurrences in each whole blob.  Scoping this to
+	 * a -L range is left to a follow-up; for now -S ignores the range.
+	 */
 	unsigned int c1 = one ? contains(one, regexp, kws, 0) : 0;
 	unsigned int c2 = two ? contains(two, regexp, kws, c1 + 1) : 0;
 	return c1 != c2;
@@ -132,6 +146,7 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	struct userdiff_driver *textconv_one = NULL;
 	struct userdiff_driver *textconv_two = NULL;
 	mmfile_t mf1, mf2;
+	const struct range_set *ranges;
 	int ret;
 
 	/* ignore unmerged */
@@ -169,7 +184,13 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	mf1.size = fill_textconv(o->repo, textconv_one, p->one, &mf1.ptr);
 	mf2.size = fill_textconv(o->repo, textconv_two, p->two, &mf2.ptr);
 
-	ret = fn(&mf1, &mf2, o, regexp, kws);
+	/*
+	 * -L scopes the search to the tracked range, but the range is in
+	 * original-file line coordinates that do not map onto textconv
+	 * output, so search the whole file when textconv is in play.
+	 */
+	ranges = (textconv_one || textconv_two) ? NULL : p->line_ranges;
+	ret = fn(&mf1, &mf2, o, regexp, kws, ranges);
 
 	if (textconv_one)
 		free(mf1.ptr);
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 68576418f4..bac74d4479 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -722,9 +722,9 @@ test_expect_success '-L with -S filters to string-count changes' '
 test_expect_success '-L with -G filters to diff-text matches' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c -G "F2 [+] 2" --format= >actual &&
-	# -G greps the whole-file diff text, not just the tracked range;
-	# combined with -L, this selects commits that both touch func2
-	# and have "F2 + 2" in their diff.
+	# -G greps the diff text, and under -L only the lines in the
+	# tracked range (unlike -S above, which searches the whole file);
+	# this selects commits whose change to func2 contains "F2 + 2".
 	test $(grep -c "^diff --git" actual) = 1 &&
 	grep "F2 + 2" actual
 '
@@ -1110,4 +1110,70 @@ test_expect_success '--check does not report blank-at-eof outside the range' '
 	test_grep ! "blank line at EOF" actual
 '
 
+test_expect_success '-L -G is scoped to the tracked range' '
+	git checkout --orphan grep-scope &&
+	git reset --hard &&
+	cat >gp.c <<-\EOF &&
+	int func1()
+	{
+	    return ALPHA;
+	}
+
+	int func2()
+	{
+	    return BETA;
+	}
+	EOF
+	git add gp.c &&
+	test_tick &&
+	git commit -m "add gp.c" &&
+	sed -e "s/ALPHA/ALPHA2/" -e "s/BETA/BETA2/" gp.c >tmp &&
+	mv tmp gp.c &&
+	git commit -a -m "touch both functions" &&
+	# The commit changes ALPHA (func1) and BETA (func2).  Tracking func2,
+	# -G BETA matches its in-range change; -G ALPHA must not, since ALPHA
+	# changes only outside the tracked range.
+	git log -L:func2:gp.c -G BETA --format=%s >actual &&
+	test_grep "touch both functions" actual &&
+	git log -L:func2:gp.c -G ALPHA --format=%s >actual &&
+	test_grep ! "touch both functions" actual
+'
+
+test_expect_success '-L -G searches the whole file under textconv' '
+	git checkout --orphan grep-textconv &&
+	git reset --hard &&
+	cat >tc.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+	EOF
+	git add tc.c &&
+	test_tick &&
+	git commit -m "add tc.c" &&
+	# One commit changes func1 and func2; MAGIC lands only in the
+	# func2 change, outside func1.
+	sed -e "s/F1/F1 + 1/" -e "s/return F2/return MAGIC/" tc.c >tmp &&
+	mv tmp tc.c &&
+	git commit -a -m "change both funcs" &&
+	echo "tc.c diff=tc" >.gitattributes &&
+
+	# Without a textconv driver, -G is scoped to func1, so MAGIC (only
+	# in the func2 change) does not select the commit.
+	git log -L:func1:tc.c -G MAGIC --format=%s --no-patch >actual &&
+	test_must_be_empty actual &&
+
+	# A textconv driver makes the range (original-file line numbers)
+	# meaningless against the driver output, so -G falls back to the
+	# whole file and MAGIC now selects the commit.
+	git config diff.tc.textconv cat &&
+	git log -L:func1:tc.c -G MAGIC --format=%s --no-patch >actual &&
+	test_grep "change both funcs" actual
+'
+
 test_done
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 51c88296ed..71e5dffefb 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -46,6 +46,19 @@ int xdi_diff_outf(mmfile_t *mf1, mmfile_t *mf2,
 		  xdiff_emit_line_fn line_fn,
 		  void *consume_callback_data,
 		  xpparam_t const *xpp, xdemitconf_t const *xecfg);
+
+struct range_set;
+/*
+ * Like xdi_diff_outf(), but forwards only the lines within the given
+ * (post-image) line ranges to line_fn, as "git log -L" scopes its output.
+ * Returns line_fn's latched return value (so a consumer can signal a hit
+ * with a non-zero return), or non-zero on xdiff failure.  Defined in
+ * diff.c (it reuses the line-range filter there).
+ */
+int diff_emit_line_ranges(mmfile_t *mf1, mmfile_t *mf2,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg);
 int read_mmfile(mmfile_t *ptr, const char *filename);
 void read_mmblob(mmfile_t *ptr, struct object_database *odb,
 		 const struct object_id *oid);
-- 
gitgitgadget

Re: [PATCH 0/7] line-log: range-scope stat, check, and -G under -L

[Michael Montalbo]

Friendly ping.

[PATCH v3 0/7] line-log: scope stat, check, and -G to -L line ranges

[Michael Montalbo via GitGitGadget]

Teach -L to work with the --stat family of options and --check. Also, teach
-G to search within the line ranges specified by -L. This series continues
the previous work[1][2] extending -L to work with more diff options, and,
for example, enables:

Reviewing the --stat history of a single function:

$ git log --oneline -L:strbuf_grow:strbuf.c --stat
c13d0f7bd4 strbuf: use st_add3() in strbuf_grow()
 strbuf.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)
...
b449f4cfc9 Rework strbuf API and semantics.
 strbuf.c | 6 ++++++
 1 file changed, 6 insertions(+)


Finding where a pattern changed inside one function with -G, while ignoring
matches elsewhere in the file:

$ git log --oneline -L:run_builtin:git.c -G RUN_SETUP
e5b17bda8b git: ensure correct git directory setup with -h
27bd38d4e5 git.c: treat RUN_SETUP_GENTLY and RUN_SETUP as mutually exclusive
...
47d0b4ff57 Clean up internal command handling


The first 4 commits are preparatory cleanup for the main feature changes and
could potentially be separated. The last 3 commits implement the new
features.

Patches:

 1. Rename line_range_callback to line_range_filter to more accurately
    reflect its role as a general filter for other diff features. Also,
    replace verbose comments with descriptive field and variable names.
 2. Simplify line-range filtering logic, which fixes a bug as a result.
 3. Make -L diff hunk header format consistent with default mode's header
    format for all cases by exposing xdiff's header generating function.
 4. Extract a line-range diff helper so the --stat, --check, and -G support
    can reuse it.
 5. Enable support for --stat family of options.
 6. Enable support for --check.
 7. Teach -G to search within -L line ranges.

Changes since v2:

 * Rewrite all prose in series from scratch to remove significant verbosity
   and extraneous detail that makes the series hard to reason about. Replace
   block comments with descriptive field and variable names.
 * Pare down and simplify some test implementations.
 * No other logical behavior changes.

[1]
https://lore.kernel.org/git/pull.2094.v3.git.1780001267.gitgitgadget@gmail.com/
[2]
https://lore.kernel.org/git/pull.2099.git.1777230630020.gitgitgadget@gmail.com/

Cc: "D. Ben Knoble" ben.knoble@gmail.com

Michael Montalbo (7):
  diff: rename line-range filter struct and clarify fields
  diff: simplify the line-range filter by classifying removals
    immediately
  diff: emit -L hunk headers via xdiff's formatter
  diff: extract a line-range diff helper for reuse
  diff: support stat formats with -L
  diff: support --check with -L line ranges
  diffcore-pickaxe: limit -G to the -L tracked range

 Documentation/line-range-options.adoc    |  15 +-
 diff.c                                   | 422 +++++++++++------------
 diffcore-pickaxe.c                       |  30 +-
 revision.c                               |   6 +-
 t/t4211-line-log.sh                      | 325 +++++++++++++++--
 t/t4211/sha1/expect.no-assertion-error   |   2 +-
 t/t4211/sha1/expect.vanishes-early       |   6 +-
 t/t4211/sha256/expect.no-assertion-error |   2 +-
 t/t4211/sha256/expect.vanishes-early     |   6 +-
 xdiff-interface.c                        |  19 +
 xdiff-interface.h                        |  23 ++
 11 files changed, 588 insertions(+), 268 deletions(-)


base-commit: 3cb9185f65410273787f74333cc027d2ea5daada
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2152%2Fmmontalbo%2Fmm%2Fline-log-stat-formats-followup-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2152/mmontalbo/mm/line-log-stat-formats-followup-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/2152

Range-diff vs v2:

 1:  6cfaccab92 ! 1:  331c6c92f3 diff: rename and group the line-range filter for clarity
     @@ Metadata
      Author: Michael Montalbo <mmontalbo@gmail.com>
      
       ## Commit message ##
     -    diff: rename and group the line-range filter for clarity
     +    diff: rename line-range filter struct and clarify fields
      
     -    The line-range filter that mm/line-log-cleanup added uses names that
     -    obscure its model.  The cursors lno_post/lno_pre and the index lno_0
     -    share an lno_ prefix but conflate the pre/post-image axis with the
     -    0-based/1-based axis, the hunk state is a flat set of rhunk_* fields,
     -    and the filter-state pointer is just s.
     +    diff's line-range filtering logic uses the line_range_callback
     +    struct to represent filtering state. However, this name does not
     +    clearly reflect the role it plays. This is especially relevant as
     +    we expand diff's line-range filtering to work with more options,
     +    including --stat and -G.
      
     -    The filter bridges two layers of diff.c, and its fields already used
     -    each layer's vocabulary, but in cryptic abbreviations.  Spell them out
     -    to the form the rest of the file uses, so that the patches that follow
     -    can simplify and fix it with those clearer names in place:
     +    Also, line_range_callback's fields are terse, while the comment
     +    explaining line_range_callback is verbose and out of place compared to
     +    its surroundings.
      
     -      - lno_post/lno_pre -> lno_in_postimage/lno_in_preimage, the
     -        line-number cursors, matching the counters in struct emit_callback
     -      - lno_0 -> idx_in_postimage, the 0-based range index
     -      - the hunk-header geometry stays old/new (old_begin, new_begin, and
     -        counts) to match the xdiff_emit_hunk_fn callback and the
     -        "@@ -<old> +<new> @@" header it feeds, but moves from flat rhunk_*
     -        fields into a "hunk" sub-struct, so accesses read
     -        filter->hunk.old_begin
     -      - flush_rhunk -> flush_range_hunk
     -      - the filter-state pointer in each callback: s -> filter
     +    Rename line_range_callback to line_range_filter, and replace the verbose
     +    comment with a concise one, instead preferring descriptive field and
     +    variable names that are self-explanatory over comments.
      
     -    Also rename the struct line_range_callback to line_range_filter: it is
     -    a filter over xdiff output, not merely a callback.
     -
     -    No behavior change.
     +    No logical behavior change. Some fields are grouped under a new struct
     +    in the newly renamed line_range_filter. Everything else is just a
     +    rename.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
       ## diff.c ##
      @@ diff.c: struct emit_callback {
     -  * reveals whether they precede an in-range line (flush into range hunk) or
     -  * an out-of-range line (discard).
     + };
     + 
     + /*
     +- * State for the line-range callback wrappers that sit between
     +- * xdi_diff_outf() and fn_out_consume().  xdiff produces a normal,
     +- * unfiltered diff; the wrappers intercept each hunk header and line,
     +- * track post-image position, and forward only lines that fall within
     +- * the requested ranges.  Contiguous in-range lines are collected into
     +- * range hunks and flushed with a synthetic @@ header so that
     +- * fn_out_consume() sees well-formed unified-diff fragments.
     +- *
     +- * Removal lines ('-') cannot be classified by post-image position, so
     +- * they are buffered in pending_rm until the next '+' or ' ' line
     +- * reveals whether they precede an in-range line (flush into range hunk) or
     +- * an out-of-range line (discard).
     ++ * Filter the line ranges that are emitted by diff.
        */
      -struct line_range_callback {
      +struct line_range_filter {
       	xdiff_emit_line_fn orig_line_fn;
       	void *orig_cb_data;
     - 	const struct range_set *ranges;	/* 0-based [start, end) */
     - 	unsigned int cur_range;		/* index into the range_set */
     - 
     - 	/* Post/pre-image line counters (1-based, set from hunk headers) */
     +-	const struct range_set *ranges;	/* 0-based [start, end) */
     +-	unsigned int cur_range;		/* index into the range_set */
     +-
     +-	/* Post/pre-image line counters (1-based, set from hunk headers) */
      -	long lno_post;
      -	long lno_pre;
     -+	long lno_in_postimage;
     -+	long lno_in_preimage;
     - 
     - 	/*
     - 	 * Function name from most recent xdiff hunk header;
     -@@ diff.c: struct line_range_callback {
     - 	char func[80];
     - 	long funclen;
     - 
     ++	const struct range_set *range_sets_to_filter_by;
     ++	unsigned int range_set_idx;
     ++
     ++	struct {
     ++		char func_name[80];
     ++		long func_name_len;
     ++		long old_begin, old_count;
     ++		long new_begin, new_count;
     ++		long lno_in_preimage;
     ++		long lno_in_postimage;
     ++		struct strbuf lines;
     ++		int active;
     ++		int has_changes;
     ++	} accumulating_hunk;
     + 
     +-	/*
     +-	 * Function name from most recent xdiff hunk header;
     +-	 * size matches struct func_line.buf in xdiff/xemit.c.
     +-	 */
     +-	char func[80];
     +-	long funclen;
     +-
      -	/* Range hunk being accumulated for the current range */
      -	struct strbuf rhunk;
      -	long rhunk_old_begin, rhunk_old_count;
      -	long rhunk_new_begin, rhunk_new_count;
      -	int rhunk_active;
      -	int rhunk_has_changes;		/* any '+' or '-' lines? */
     -+	/* The range hunk being accumulated for the current range. */
     -+	struct {
     -+		struct strbuf lines;	/* buffered in-range diff lines */
     -+		long old_begin, old_count;
     -+		long new_begin, new_count;
     -+		int active;
     -+		int has_changes;	/* any '+' or '-' line? */
     -+	} hunk;
     - 
     - 	/* Removal lines not yet known to be in-range */
     +-
     +-	/* Removal lines not yet known to be in-range */
       	struct strbuf pending_rm;
     + 	int pending_rm_count;
     +-	long pending_rm_pre_begin;	/* pre-image line of first pending */
     ++	long pending_rm_pre_begin;
     + 
     +-	int ret;			/* latched error from orig_line_fn */
     ++	int ret;
     + };
     + 
     + static int count_lines(const char *data, int size)
      @@ diff.c: static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
       	return 1;
       }
     @@ diff.c: static int quick_consume(void *priv, char *line UNUSED, unsigned long le
      +static void flush_range_hunk(struct line_range_filter *filter)
       {
       	struct strbuf hdr = STRBUF_INIT;
     - 	const char *p, *end;
     +-	const char *p, *end;
     ++	const char *line_buf, *line_buf_end;
       
      -	if (!s->rhunk_active || s->ret)
     -+	if (!filter->hunk.active || filter->ret)
     ++	if (!filter->accumulating_hunk.active || filter->ret)
       		return;
       
     - 	/* Drain any pending removal lines into the range hunk */
     +-	/* Drain any pending removal lines into the range hunk */
      -	if (s->pending_rm_count) {
      -		strbuf_addbuf(&s->rhunk, &s->pending_rm);
      -		s->rhunk_old_count += s->pending_rm_count;
      -		s->rhunk_has_changes = 1;
      -		discard_pending_rm(s);
      +	if (filter->pending_rm_count) {
     -+		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
     -+		filter->hunk.old_count += filter->pending_rm_count;
     -+		filter->hunk.has_changes = 1;
     ++		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
     ++		filter->accumulating_hunk.old_count += filter->pending_rm_count;
     ++		filter->accumulating_hunk.has_changes = 1;
      +		discard_pending_rm(filter);
       	}
       
     - 	/*
     -@@ diff.c: static void flush_rhunk(struct line_range_callback *s)
     - 	 * ctxlen causes xdiff to emit context covering a range that
     - 	 * has no changes in this commit.
     - 	 */
     +-	/*
     +-	 * Suppress context-only hunks: they contain no actual changes
     +-	 * and would just be noise.  This can happen when the inflated
     +-	 * ctxlen causes xdiff to emit context covering a range that
     +-	 * has no changes in this commit.
     +-	 */
      -	if (!s->rhunk_has_changes) {
      -		s->rhunk_active = 0;
      -		strbuf_reset(&s->rhunk);
     -+	if (!filter->hunk.has_changes) {
     -+		filter->hunk.active = 0;
     -+		strbuf_reset(&filter->hunk.lines);
     ++	if (!filter->accumulating_hunk.has_changes) {
     ++		filter->accumulating_hunk.active = 0;
     ++		strbuf_reset(&filter->accumulating_hunk.lines);
       		return;
       	}
       
     @@ diff.c: static void flush_rhunk(struct line_range_callback *s)
      -		    s->rhunk_old_begin, s->rhunk_old_count,
      -		    s->rhunk_new_begin, s->rhunk_new_count);
      -	if (s->funclen > 0) {
     -+		    filter->hunk.old_begin, filter->hunk.old_count,
     -+		    filter->hunk.new_begin, filter->hunk.new_count);
     -+	if (filter->funclen > 0) {
     ++		    filter->accumulating_hunk.old_begin, filter->accumulating_hunk.old_count,
     ++		    filter->accumulating_hunk.new_begin, filter->accumulating_hunk.new_count);
     ++	if (filter->accumulating_hunk.func_name_len > 0) {
       		strbuf_addch(&hdr, ' ');
      -		strbuf_add(&hdr, s->func, s->funclen);
     -+		strbuf_add(&hdr, filter->func, filter->funclen);
     ++		strbuf_add(&hdr, filter->accumulating_hunk.func_name,
     ++	     filter->accumulating_hunk.func_name_len);
       	}
       	strbuf_addch(&hdr, '\n');
       
     @@ diff.c: static void flush_rhunk(struct line_range_callback *s)
      +	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
       	strbuf_release(&hdr);
       
     - 	/*
     -@@ diff.c: static void flush_rhunk(struct line_range_callback *s)
     - 	 * The cast discards const because xdiff_emit_line_fn takes
     - 	 * char *, though fn_out_consume does not modify the buffer.
     - 	 */
     +-	/*
     +-	 * Replay buffered lines one at a time through fn_out_consume.
     +-	 * The cast discards const because xdiff_emit_line_fn takes
     +-	 * char *, though fn_out_consume does not modify the buffer.
     +-	 */
      -	p = s->rhunk.buf;
      -	end = p + s->rhunk.len;
      -	while (!s->ret && p < end) {
     -+	p = filter->hunk.lines.buf;
     -+	end = p + filter->hunk.lines.len;
     -+	while (!filter->ret && p < end) {
     - 		const char *eol = memchr(p, '\n', end - p);
     - 		unsigned long line_len = eol ? (unsigned long)(eol - p + 1)
     - 					     : (unsigned long)(end - p);
     +-		const char *eol = memchr(p, '\n', end - p);
     +-		unsigned long line_len = eol ? (unsigned long)(eol - p + 1)
     +-					     : (unsigned long)(end - p);
      -		s->ret = s->orig_line_fn(s->orig_cb_data, (char *)p, line_len);
     -+		filter->ret = filter->orig_line_fn(filter->orig_cb_data, (char *)p, line_len);
     - 		p += line_len;
     +-		p += line_len;
     ++	line_buf = filter->accumulating_hunk.lines.buf;
     ++	line_buf_end = line_buf + filter->accumulating_hunk.lines.len;
     ++	while (!filter->ret && line_buf < line_buf_end) {
     ++		const char *eol = memchr(line_buf, '\n', line_buf_end - line_buf);
     ++		unsigned long line_len = eol ? (unsigned long)(eol - line_buf + 1)
     ++					     : (unsigned long)(line_buf_end - line_buf);
     ++		filter->ret = filter->orig_line_fn(filter->orig_cb_data,
     ++				     (char *)line_buf, line_len);
     ++		line_buf += line_len;
       	}
       
      -	s->rhunk_active = 0;
      -	strbuf_reset(&s->rhunk);
     -+	filter->hunk.active = 0;
     -+	strbuf_reset(&filter->hunk.lines);
     ++	filter->accumulating_hunk.active = 0;
     ++	strbuf_reset(&filter->accumulating_hunk.lines);
       }
       
       static void line_range_hunk_fn(void *data,
     @@ diff.c: static void line_range_hunk_fn(void *data,
      -	struct line_range_callback *s = data;
      +	struct line_range_filter *filter = data;
       
     - 	/*
     - 	 * When count > 0, begin is 1-based.  When count == 0, begin is
     -@@ diff.c: static void line_range_hunk_fn(void *data,
     - 	 * flush or discard them when the next content line reveals
     - 	 * whether the removals precede in-range content.
     - 	 */
     +-	/*
     +-	 * When count > 0, begin is 1-based.  When count == 0, begin is
     +-	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
     +-	 * that type will arrive, so the value is unused.
     +-	 *
     +-	 * Any pending removal lines from the previous xdiff hunk are
     +-	 * intentionally left in pending_rm: the line callback will
     +-	 * flush or discard them when the next content line reveals
     +-	 * whether the removals precede in-range content.
     +-	 */
      -	s->lno_post = new_begin;
      -	s->lno_pre = old_begin;
     -+	filter->lno_in_postimage = new_begin;
     -+	filter->lno_in_preimage = old_begin;
     ++	filter->accumulating_hunk.lno_in_postimage = new_begin;
     ++	filter->accumulating_hunk.lno_in_preimage = old_begin;
       
       	if (funclen > 0) {
      -		if (funclen > (long)sizeof(s->func))
      -			funclen = sizeof(s->func);
      -		memcpy(s->func, func, funclen);
     -+		if (funclen > (long)sizeof(filter->func))
     -+			funclen = sizeof(filter->func);
     -+		memcpy(filter->func, func, funclen);
     ++		if (funclen > (long)sizeof(filter->accumulating_hunk.func_name))
     ++			funclen = sizeof(filter->accumulating_hunk.func_name);
     ++		memcpy(filter->accumulating_hunk.func_name, func, funclen);
       	}
      -	s->funclen = funclen;
     -+	filter->funclen = funclen;
     ++	filter->accumulating_hunk.func_name_len = funclen;
       }
       
       static int line_range_line_fn(void *priv, char *line, unsigned long len)
     @@ diff.c: static void line_range_hunk_fn(void *data,
      -		s->pending_rm_count++;
      -		return s->ret;
      +		if (!filter->pending_rm_count)
     -+			filter->pending_rm_pre_begin = filter->lno_in_preimage;
     -+		filter->lno_in_preimage++;
     ++			filter->pending_rm_pre_begin =
     ++				filter->accumulating_hunk.lno_in_preimage;
     ++		filter->accumulating_hunk.lno_in_preimage++;
      +		strbuf_add(&filter->pending_rm, line, len);
      +		filter->pending_rm_count++;
      +		return filter->ret;
     @@ diff.c: static void line_range_hunk_fn(void *data,
      -			strbuf_add(&s->pending_rm, line, len);
      -		else if (s->rhunk_active)
      -			strbuf_add(&s->rhunk, line, len);
     +-		/* otherwise outside tracked range; drop silently */
     +-		return s->ret;
      +		if (filter->pending_rm_count)
      +			strbuf_add(&filter->pending_rm, line, len);
     -+		else if (filter->hunk.active)
     -+			strbuf_add(&filter->hunk.lines, line, len);
     - 		/* otherwise outside tracked range; drop silently */
     --		return s->ret;
     ++		else if (filter->accumulating_hunk.active)
     ++			strbuf_add(&filter->accumulating_hunk.lines, line, len);
      +		return filter->ret;
       	}
       
     @@ diff.c: static void line_range_hunk_fn(void *data,
      -	lno_0 = s->lno_post - 1;
      -	cur_pre = s->lno_pre;	/* save before advancing for context lines */
      -	s->lno_post++;
     -+	idx_in_postimage = filter->lno_in_postimage - 1;
     -+	cur_pre = filter->lno_in_preimage;	/* save before advancing for context lines */
     -+	filter->lno_in_postimage++;
     ++	idx_in_postimage = filter->accumulating_hunk.lno_in_postimage - 1;
     ++	cur_pre = filter->accumulating_hunk.lno_in_preimage;
     ++	filter->accumulating_hunk.lno_in_postimage++;
       	if (line[0] == ' ')
      -		s->lno_pre++;
     -+		filter->lno_in_preimage++;
     ++		filter->accumulating_hunk.lno_in_preimage++;
       
     - 	/* Advance past ranges we've passed */
     +-	/* Advance past ranges we've passed */
      -	while (s->cur_range < s->ranges->nr &&
      -	       lno_0 >= s->ranges->ranges[s->cur_range].end) {
      -		if (s->rhunk_active)
      -			flush_rhunk(s);
      -		discard_pending_rm(s);
      -		s->cur_range++;
     -+	while (filter->cur_range < filter->ranges->nr &&
     -+	       idx_in_postimage >= filter->ranges->ranges[filter->cur_range].end) {
     -+		if (filter->hunk.active)
     ++	while (filter->range_set_idx < filter->range_sets_to_filter_by->nr &&
     ++	       idx_in_postimage >=
     ++		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].end) {
     ++		if (filter->accumulating_hunk.active)
      +			flush_range_hunk(filter);
      +		discard_pending_rm(filter);
     -+		filter->cur_range++;
     ++		filter->range_set_idx++;
       	}
       
     - 	/* Past all ranges */
     +-	/* Past all ranges */
      -	if (s->cur_range >= s->ranges->nr) {
      -		discard_pending_rm(s);
      -		return s->ret;
     -+	if (filter->cur_range >= filter->ranges->nr) {
     ++	if (filter->range_set_idx >= filter->range_sets_to_filter_by->nr) {
      +		discard_pending_rm(filter);
      +		return filter->ret;
       	}
       
      -	cur = &s->ranges->ranges[s->cur_range];
     -+	cur = &filter->ranges->ranges[filter->cur_range];
     ++	cur = &filter->range_sets_to_filter_by->ranges[filter->range_set_idx];
       
     - 	/* Before current range */
     +-	/* Before current range */
      -	if (lno_0 < cur->start) {
      -		discard_pending_rm(s);
      -		return s->ret;
     @@ diff.c: static void line_range_hunk_fn(void *data,
      +		return filter->ret;
       	}
       
     - 	/* In range so start a new range hunk if needed */
     +-	/* In range so start a new range hunk if needed */
      -	if (!s->rhunk_active) {
      -		s->rhunk_active = 1;
      -		s->rhunk_has_changes = 0;
     @@ diff.c: static void line_range_hunk_fn(void *data,
      -		s->rhunk_old_count = 0;
      -		s->rhunk_new_count = 0;
      -		strbuf_reset(&s->rhunk);
     -+	if (!filter->hunk.active) {
     -+		filter->hunk.active = 1;
     -+		filter->hunk.has_changes = 0;
     -+		filter->hunk.new_begin = idx_in_postimage + 1;
     -+		filter->hunk.old_begin = filter->pending_rm_count
     ++	if (!filter->accumulating_hunk.active) {
     ++		filter->accumulating_hunk.active = 1;
     ++		filter->accumulating_hunk.has_changes = 0;
     ++		filter->accumulating_hunk.new_begin = idx_in_postimage + 1;
     ++		filter->accumulating_hunk.old_begin = filter->pending_rm_count
      +			? filter->pending_rm_pre_begin : cur_pre;
     -+		filter->hunk.old_count = 0;
     -+		filter->hunk.new_count = 0;
     -+		strbuf_reset(&filter->hunk.lines);
     ++		filter->accumulating_hunk.old_count = 0;
     ++		filter->accumulating_hunk.new_count = 0;
     ++		strbuf_reset(&filter->accumulating_hunk.lines);
       	}
       
     - 	/* Flush pending removals into range hunk */
     +-	/* Flush pending removals into range hunk */
      -	if (s->pending_rm_count) {
      -		strbuf_addbuf(&s->rhunk, &s->pending_rm);
      -		s->rhunk_old_count += s->pending_rm_count;
      -		s->rhunk_has_changes = 1;
      -		discard_pending_rm(s);
      +	if (filter->pending_rm_count) {
     -+		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
     -+		filter->hunk.old_count += filter->pending_rm_count;
     -+		filter->hunk.has_changes = 1;
     ++		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
     ++		filter->accumulating_hunk.old_count += filter->pending_rm_count;
     ++		filter->accumulating_hunk.has_changes = 1;
      +		discard_pending_rm(filter);
       	}
       
      -	strbuf_add(&s->rhunk, line, len);
      -	s->rhunk_new_count++;
     -+	strbuf_add(&filter->hunk.lines, line, len);
     -+	filter->hunk.new_count++;
     ++	strbuf_add(&filter->accumulating_hunk.lines, line, len);
     ++	filter->accumulating_hunk.new_count++;
       	if (line[0] == '+')
      -		s->rhunk_has_changes = 1;
     -+		filter->hunk.has_changes = 1;
     ++		filter->accumulating_hunk.has_changes = 1;
       	else
      -		s->rhunk_old_count++;
     -+		filter->hunk.old_count++;
     ++		filter->accumulating_hunk.old_count++;
       
      -	return s->ret;
      +	return filter->ret;
     @@ diff.c: static void builtin_diff(const char *name_a,
       			unsigned int i;
       			long max_span = 0;
       
     -@@ diff.c: static void builtin_diff(const char *name_a,
     + 			memset(&lr_state, 0, sizeof(lr_state));
       			lr_state.orig_line_fn = fn_out_consume;
       			lr_state.orig_cb_data = &ecbdata;
     - 			lr_state.ranges = line_ranges;
     +-			lr_state.ranges = line_ranges;
      -			strbuf_init(&lr_state.rhunk, 0);
     -+			strbuf_init(&lr_state.hunk.lines, 0);
     ++			lr_state.range_sets_to_filter_by = line_ranges;
     ++			strbuf_init(&lr_state.accumulating_hunk.lines, 0);
       			strbuf_init(&lr_state.pending_rm, 0);
       
       			/*
     @@ diff.c: static void builtin_diff(const char *name_a,
       				die("unable to generate diff for %s",
       				    one->path);
      -			strbuf_release(&lr_state.rhunk);
     -+			strbuf_release(&lr_state.hunk.lines);
     ++			strbuf_release(&lr_state.accumulating_hunk.lines);
       			strbuf_release(&lr_state.pending_rm);
       		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
       					 &ecbdata, &xpp, &xecfg))
 2:  5602b7976a ! 2:  020e07c0ea diff: simplify the line-range filter by classifying removals immediately
     @@ Metadata
       ## Commit message ##
          diff: simplify the line-range filter by classifying removals immediately
      
     -    The filter buffered '-' lines in a pending_rm strbuf, deferring their
     -    classification until a '+' or ' ' line revealed the post-image
     -    position.  That buffering is unnecessary: a removal occupies no
     -    post-image line, so it does not advance lno_in_postimage, and xdiff
     -    emits removals before additions within a change.  A '-' therefore
     -    arrives while lno_in_postimage already holds the index the following
     -    '+'/' ' will occupy, and can be classified against the ranges as it
     -    arrives.
     +    Currently, the diff line-range filter buffers preimage removal lines
     +    until a postimage line arrives. That line's number confirms whether the
     +    preimage line falls in a relevant range. However, storing preimage
     +    lines in a separate buffer is unnecessary. Worse, the logic has a bug:
     +    a preimage line outside the target range is included when it
     +    immediately follows an in-range postimage line.
      
     -    The buffering also hid a bug: flush_range_hunk() drained pending_rm into
     -    the range hunk whenever the hunk was active, even after lno_in_postimage
     -    had advanced past the tracked range, so a deletion just after the
     -    tracked function leaked into the patch.  Classifying each line as it
     -    arrives removes the pending_rm buffer, the discard_pending_rm() helper,
     -    three struct fields, and makes that bug impossible by construction.
     +    Preimage lines will always precede their postimage counterpart both in
     +    content line number and emission order from xdiff's line callback
     +    function. So preimage lines can share the postimage buffer. The filter
     +    flushes them based on whether the postimage lines fall within the
     +    target range.
      
     -    With every line classified on arrival, the buffered lines are the
     -    hunk's single source of truth, so the old/new counts need not be kept
     -    alongside them: flush_range_hunk() derives the counts (and whether the
     -    hunk holds any change) from the buffer when it builds the header.  Drop
     -    the per-line counting and the old_count, new_count, and has_changes
     -    fields; there is no longer a second tally that could fall out of sync
     -    with the buffer.
     +    Remove logic related to storing preimage lines in a separate "removal"
     +    buffer and prepending them to the accumulating_hunk's line buffer.
     +    Instead, store those lines in the accumulating_hunk's line_buffer
     +    immediately and flush everything as appropriate based on postimage
     +    line numbers that arrive. This resolves the bug by construction.
      
     -    Add begin_range_hunk() to open the accumulator at the first in-range
     -    line, seeding both begins from the live image cursors, as the
     -    counterpart to flush_range_hunk().  With the counting gone too,
     -    line_range_line_fn() now only appends an in-range line.
     +    Also, calculate the old and new line counts for the diff hunk header
     +    when flushing rather than storing counters in line_range_filter to
     +    simplify state management further.
      
     -    Document the coordinate model: a block comment on struct
     -    line_range_filter states it (the pre/post-image cursors, the 0-based
     -    idx_in_postimage, removals classified by the following line) with a
     -    worked example.
     -
     -    Add tests for the leaked trailing deletion this fixes, the symmetric
     -    leading-deletion case, and the filter's range boundaries (a change at
     -    the first and last line of a range, and a pure in-range deletion).
     +    Add a test to t/t4211-line-log.sh that verifies the preimage line
     +    emission bug is fixed.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
       ## diff.c ##
     -@@ diff.c: struct emit_callback {
     - };
     - 
     - /*
     -- * State for the line-range callback wrappers that sit between
     -- * xdi_diff_outf() and fn_out_consume().  xdiff produces a normal,
     -- * unfiltered diff; the wrappers intercept each hunk header and line,
     -- * track post-image position, and forward only lines that fall within
     -- * the requested ranges.  Contiguous in-range lines are collected into
     -- * range hunks and flushed with a synthetic @@ header so that
     -- * fn_out_consume() sees well-formed unified-diff fragments.
     -+ * Line-range filter: scopes "git log -L" output to the tracked ranges.
     -  *
     -- * Removal lines ('-') cannot be classified by post-image position, so
     -- * they are buffered in pending_rm until the next '+' or ' ' line
     -- * reveals whether they precede an in-range line (flush into range hunk) or
     -- * an out-of-range line (discard).
     -+ * It sits between xdi_diff_outf() and an output callback (fn_out_consume,
     -+ * diffstat_consume, checkdiff_consume).  xdiff produces a normal diff; the
     -+ * filter forwards only the lines inside the requested ranges, collecting
     -+ * contiguous in-range lines into a "range hunk" emitted with a synthetic
     -+ * @@ header so the callback sees well-formed unified-diff fragments.
     -+ *
     -+ * A diff describes the change from a pre-image to a post-image.  Each
     -+ * line is context (' ', in both), a removal ('-', pre-image only), or
     -+ * an addition ('+', post-image only).  -L tracks ranges in the
     -+ * post-image, so a line is in range by its post-image position.
     -+ *
     -+ * Two 1-based cursors track the next line in each image, named as in
     -+ * struct emit_callback and seeded from the xdiff hunk header:
     -+ *
     -+ *	lno_in_postimage  advances on '+' and ' '   (lines in the post-image)
     -+ *	lno_in_preimage   advances on '-' and ' '   (lines in the pre-image)
     -+ *
     -+ * Ranges are 0-based half-open [start, end), so a line is tested at the
     -+ * 0-based index idx_in_postimage = lno_in_postimage - 1.
     -+ *
     -+ * A '-' is not present in the post-image, so it has no post-image line
     -+ * number of its own.  Since it does not advance lno_in_postimage, it is
     -+ * classified at the idx_in_postimage that the following '+'/' ' will
     -+ * occupy.  xdiff emits a change's removals before its additions, so that
     -+ * index is already known when the '-' arrives.
     -+ *
     -+ * The synthetic "@@ -<old> +<new> @@" header has two sides, old (the
     -+ * pre-image) and new (the post-image), matching the xdiff_emit_hunk_fn
     -+ * callback; the hunk.old_begin / hunk.new_begin fields below hold those
     -+ * begins, and flush_range_hunk() derives the counts from the buffered
     -+ * lines.
     -+ *
     -+ * Example, tracking post-image line 2 (range [1, 2)) of:
     -+ *
     -+ *	pre-image  post-image
     -+ *	1 a        1 a
     -+ *	2 b        2 X      (b -> X)
     -+ *	3 c        3 c
     -+ *
     -+ *	classify each line by idx_in_postimage.  The pre and post columns
     -+ *	are each cursor's value while that line is classified, i.e. before
     -+ *	the line advances them (pre = lno_in_preimage,
     -+ *	post = lno_in_postimage, idx = idx_in_postimage):
     -+ *	' a'  pre 1  post 1  idx 0  ->  before start, skip
     -+ *	'-b'  pre 2  post 2  idx 1  ->  keep (removal)
     -+ *	'+X'  pre 3  post 2  idx 1  ->  keep (addition)
     -+ *	' c'  pre 3  post 3  idx 2  ->  past end, flush
     -+ *
     -+ * -b and +X share idx = 1 because -b did not advance lno_in_postimage;
     -+ * both land in the range hunk, flushed when ' c' crosses the range end.
     -  */
     - struct line_range_filter {
     - 	xdiff_emit_line_fn orig_line_fn;
      @@ diff.c: struct line_range_filter {
     - 	char func[80];
     - 	long funclen;
     - 
     --	/* The range hunk being accumulated for the current range. */
     -+	/*
     -+	 * The range hunk being accumulated.  At most one is live at a time:
     -+	 * it is flushed and reset as the cursor leaves each range (and once
     -+	 * more at end of diff), then reused for the next range.
     -+	 */
       	struct {
     - 		struct strbuf lines;	/* buffered in-range diff lines */
     + 		char func_name[80];
     + 		long func_name_len;
      -		long old_begin, old_count;
      -		long new_begin, new_count;
      +		long old_begin;
      +		long new_begin;
     + 		long lno_in_preimage;
     + 		long lno_in_postimage;
     + 		struct strbuf lines;
       		int active;
     --		int has_changes;	/* any '+' or '-' line? */
     - 	} hunk;
     +-		int has_changes;
     + 	} accumulating_hunk;
       
     --	/* Removal lines not yet known to be in-range */
      -	struct strbuf pending_rm;
      -	int pending_rm_count;
     --	long pending_rm_pre_begin;	/* pre-image line of first pending */
     +-	long pending_rm_pre_begin;
      -
     - 	int ret;			/* latched error from orig_line_fn */
     + 	int ret;
       };
       
      @@ diff.c: static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
     @@ diff.c: static int quick_consume(void *priv, char *line UNUSED, unsigned long le
       }
       
      -static void discard_pending_rm(struct line_range_filter *filter)
     -+/*
     -+ * Begin a range hunk at the first in-range line.  Its position fixes the
     -+ * hunk's begins, taken from the two image cursors before they advance:
     -+ * new_begin from the post-image, old_begin from the pre-image.  The line
     -+ * counts are not tracked here; flush_range_hunk() derives them from the
     -+ * buffered lines.
     -+ */
      +static void begin_range_hunk(struct line_range_filter *filter)
       {
      -	strbuf_reset(&filter->pending_rm);
      -	filter->pending_rm_count = 0;
     -+	filter->hunk.active = 1;
     -+	filter->hunk.new_begin = filter->lno_in_postimage;
     -+	filter->hunk.old_begin = filter->lno_in_preimage;
     -+	strbuf_reset(&filter->hunk.lines);
     ++	filter->accumulating_hunk.active = 1;
     ++	filter->accumulating_hunk.new_begin = filter->accumulating_hunk.lno_in_postimage;
     ++	filter->accumulating_hunk.old_begin = filter->accumulating_hunk.lno_in_preimage;
     ++	strbuf_reset(&filter->accumulating_hunk.lines);
       }
       
       static void flush_range_hunk(struct line_range_filter *filter)
       {
       	struct strbuf hdr = STRBUF_INIT;
     - 	const char *p, *end;
     + 	const char *line_buf, *line_buf_end;
      +	long old_count = 0, new_count = 0;
      +	int has_changes = 0;
       
     - 	if (!filter->hunk.active || filter->ret)
     + 	if (!filter->accumulating_hunk.active || filter->ret)
       		return;
       
     --	/* Drain any pending removal lines into the range hunk */
      -	if (filter->pending_rm_count) {
     --		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
     --		filter->hunk.old_count += filter->pending_rm_count;
     --		filter->hunk.has_changes = 1;
     +-		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
     +-		filter->accumulating_hunk.old_count += filter->pending_rm_count;
     +-		filter->accumulating_hunk.has_changes = 1;
      -		discard_pending_rm(filter);
     -+	/*
     -+	 * Derive the hunk's geometry from the buffered lines: a ' '
     -+	 * counts on both sides, a '-' on the old side, a '+' on the new.
     -+	 * A '-' or '+' marks a real change; the "\ No newline at end of
     -+	 * file" marker (line[0] == '\\') counts on neither side.
     -+	 */
     -+	p = filter->hunk.lines.buf;
     -+	end = p + filter->hunk.lines.len;
     -+	while (p < end) {
     -+		const char *eol = memchr(p, '\n', end - p);
     -+		if (*p == ' ' || *p == '-')
     ++	line_buf = filter->accumulating_hunk.lines.buf;
     ++	line_buf_end = line_buf + filter->accumulating_hunk.lines.len;
     ++	while (line_buf < line_buf_end) {
     ++		const char *eol = memchr(line_buf, '\n', line_buf_end - line_buf);
     ++		if (*line_buf == ' ') {
      +			old_count++;
     -+		if (*p == ' ' || *p == '+')
      +			new_count++;
     -+		if (*p == '-' || *p == '+')
     ++		}
     ++		else if (*line_buf == '-') {
     ++			old_count++;
      +			has_changes = 1;
     -+		p = eol ? eol + 1 : end;
     ++		}
     ++		else if (*line_buf == '+') {
     ++			new_count++;
     ++			has_changes = 1;
     ++		}
     ++		line_buf = eol ? eol + 1 : line_buf_end;
       	}
       
     - 	/*
     -@@ diff.c: static void flush_range_hunk(struct line_range_filter *filter)
     - 	 * ctxlen causes xdiff to emit context covering a range that
     - 	 * has no changes in this commit.
     - 	 */
     --	if (!filter->hunk.has_changes) {
     +-	if (!filter->accumulating_hunk.has_changes) {
      +	if (!has_changes) {
     - 		filter->hunk.active = 0;
     - 		strbuf_reset(&filter->hunk.lines);
     + 		filter->accumulating_hunk.active = 0;
     + 		strbuf_reset(&filter->accumulating_hunk.lines);
       		return;
       	}
       
       	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
     --		    filter->hunk.old_begin, filter->hunk.old_count,
     --		    filter->hunk.new_begin, filter->hunk.new_count);
     -+		    filter->hunk.old_begin, old_count,
     -+		    filter->hunk.new_begin, new_count);
     - 	if (filter->funclen > 0) {
     +-		    filter->accumulating_hunk.old_begin, filter->accumulating_hunk.old_count,
     +-		    filter->accumulating_hunk.new_begin, filter->accumulating_hunk.new_count);
     ++		    filter->accumulating_hunk.old_begin, old_count,
     ++		    filter->accumulating_hunk.new_begin, new_count);
     + 	if (filter->accumulating_hunk.func_name_len > 0) {
       		strbuf_addch(&hdr, ' ');
     - 		strbuf_add(&hdr, filter->func, filter->funclen);
     -@@ diff.c: static void line_range_hunk_fn(void *data,
     - 	 * When count > 0, begin is 1-based.  When count == 0, begin is
     - 	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
     - 	 * that type will arrive, so the value is unused.
     --	 *
     --	 * Any pending removal lines from the previous xdiff hunk are
     --	 * intentionally left in pending_rm: the line callback will
     --	 * flush or discard them when the next content line reveals
     --	 * whether the removals precede in-range content.
     - 	 */
     - 	filter->lno_in_postimage = new_begin;
     - 	filter->lno_in_preimage = old_begin;
     + 		strbuf_add(&hdr, filter->accumulating_hunk.func_name,
     +-	     filter->accumulating_hunk.func_name_len);
     ++			   filter->accumulating_hunk.func_name_len);
     + 	}
     + 	strbuf_addch(&hdr, '\n');
     + 
      @@ diff.c: static void line_range_hunk_fn(void *data,
       static int line_range_line_fn(void *priv, char *line, unsigned long len)
       {
     @@ diff.c: static void line_range_hunk_fn(void *data,
       
      -	if (line[0] == '-') {
      -		if (!filter->pending_rm_count)
     --			filter->pending_rm_pre_begin = filter->lno_in_preimage;
     --		filter->lno_in_preimage++;
     +-			filter->pending_rm_pre_begin =
     +-				filter->accumulating_hunk.lno_in_preimage;
     +-		filter->accumulating_hunk.lno_in_preimage++;
      -		strbuf_add(&filter->pending_rm, line, len);
      -		filter->pending_rm_count++;
      -		return filter->ret;
     @@ diff.c: static void line_range_hunk_fn(void *data,
       	if (line[0] == '\\') {
      -		if (filter->pending_rm_count)
      -			strbuf_add(&filter->pending_rm, line, len);
     --		else if (filter->hunk.active)
     -+		if (filter->hunk.active)
     - 			strbuf_add(&filter->hunk.lines, line, len);
     --		/* otherwise outside tracked range; drop silently */
     +-		else if (filter->accumulating_hunk.active)
     ++		if (filter->accumulating_hunk.active)
     + 			strbuf_add(&filter->accumulating_hunk.lines, line, len);
       		return filter->ret;
       	}
       
     @@ diff.c: static void line_range_hunk_fn(void *data,
      +	if (line[0] != '+' && line[0] != ' ' && line[0] != '-')
       		BUG("unexpected diff line type '%c'", line[0]);
       
     -+	/*
     -+	 * idx_in_postimage is this line's 0-based post-image index (see the model on
     -+	 * struct line_range_filter).  The cursors are advanced only after
     -+	 * the line is classified, so a '-' is tested at the same idx_in_postimage as
     -+	 * the '+'/' ' that follows it.
     -+	 */
     - 	idx_in_postimage = filter->lno_in_postimage - 1;
     --	cur_pre = filter->lno_in_preimage;	/* save before advancing for context lines */
     --	filter->lno_in_postimage++;
     + 	idx_in_postimage = filter->accumulating_hunk.lno_in_postimage - 1;
     +-	cur_pre = filter->accumulating_hunk.lno_in_preimage;
     +-	filter->accumulating_hunk.lno_in_postimage++;
      -	if (line[0] == ' ')
     --		filter->lno_in_preimage++;
     +-		filter->accumulating_hunk.lno_in_preimage++;
       
     --	/* Advance past ranges we've passed */
     -+	/* Retire ranges we have passed, flushing the one we leave. */
     - 	while (filter->cur_range < filter->ranges->nr &&
     - 	       idx_in_postimage >= filter->ranges->ranges[filter->cur_range].end) {
     - 		if (filter->hunk.active)
     + 	while (filter->range_set_idx < filter->range_sets_to_filter_by->nr &&
     + 	       idx_in_postimage >=
     + 		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].end) {
     + 		if (filter->accumulating_hunk.active)
       			flush_range_hunk(filter);
      -		discard_pending_rm(filter);
     - 		filter->cur_range++;
     + 		filter->range_set_idx++;
       	}
       
     --	/* Past all ranges */
     --	if (filter->cur_range >= filter->ranges->nr) {
     +-	if (filter->range_set_idx >= filter->range_sets_to_filter_by->nr) {
      -		discard_pending_rm(filter);
      -		return filter->ret;
      -	}
     -+	in_range = filter->cur_range < filter->ranges->nr &&
     -+		   idx_in_postimage >= filter->ranges->ranges[filter->cur_range].start &&
     -+		   idx_in_postimage < filter->ranges->ranges[filter->cur_range].end;
     - 
     --	cur = &filter->ranges->ranges[filter->cur_range];
     -+	if (in_range) {
     -+		if (!filter->hunk.active)
     -+			begin_range_hunk(filter);
     - 
     --	/* Before current range */
     +-
     +-	cur = &filter->range_sets_to_filter_by->ranges[filter->range_set_idx];
     +-
      -	if (idx_in_postimage < cur->start) {
      -		discard_pending_rm(filter);
      -		return filter->ret;
     -+		strbuf_add(&filter->hunk.lines, line, len);
     - 	}
     +-	}
     ++	in_range = filter->range_set_idx < filter->range_sets_to_filter_by->nr &&
     ++		   idx_in_postimage >=
     ++		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].start &&
     ++		   idx_in_postimage <
     ++		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].end;
       
     --	/* In range so start a new range hunk if needed */
     --	if (!filter->hunk.active) {
     --		filter->hunk.active = 1;
     --		filter->hunk.has_changes = 0;
     --		filter->hunk.new_begin = idx_in_postimage + 1;
     --		filter->hunk.old_begin = filter->pending_rm_count
     +-	if (!filter->accumulating_hunk.active) {
     +-		filter->accumulating_hunk.active = 1;
     +-		filter->accumulating_hunk.has_changes = 0;
     +-		filter->accumulating_hunk.new_begin = idx_in_postimage + 1;
     +-		filter->accumulating_hunk.old_begin = filter->pending_rm_count
      -			? filter->pending_rm_pre_begin : cur_pre;
     --		filter->hunk.old_count = 0;
     --		filter->hunk.new_count = 0;
     --		strbuf_reset(&filter->hunk.lines);
     +-		filter->accumulating_hunk.old_count = 0;
     +-		filter->accumulating_hunk.new_count = 0;
     +-		strbuf_reset(&filter->accumulating_hunk.lines);
      -	}
     --
     --	/* Flush pending removals into range hunk */
     ++	if (in_range) {
     ++		if (!filter->accumulating_hunk.active)
     ++			begin_range_hunk(filter);
     + 
      -	if (filter->pending_rm_count) {
     --		strbuf_addbuf(&filter->hunk.lines, &filter->pending_rm);
     --		filter->hunk.old_count += filter->pending_rm_count;
     --		filter->hunk.has_changes = 1;
     +-		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
     +-		filter->accumulating_hunk.old_count += filter->pending_rm_count;
     +-		filter->accumulating_hunk.has_changes = 1;
      -		discard_pending_rm(filter);
     --	}
     --
     --	strbuf_add(&filter->hunk.lines, line, len);
     --	filter->hunk.new_count++;
     ++		strbuf_add(&filter->accumulating_hunk.lines, line, len);
     + 	}
     + 
     +-	strbuf_add(&filter->accumulating_hunk.lines, line, len);
     +-	filter->accumulating_hunk.new_count++;
      -	if (line[0] == '+')
     --		filter->hunk.has_changes = 1;
     +-		filter->accumulating_hunk.has_changes = 1;
      -	else
     --		filter->hunk.old_count++;
     -+	/*
     -+	 * Advance each image's cursor: a line present in that image (see
     -+	 * the model) consumes one of its line numbers.
     -+	 */
     -+	if (line[0] != '-')
     -+		filter->lno_in_postimage++;
     -+	if (line[0] != '+')
     -+		filter->lno_in_preimage++;
     +-		filter->accumulating_hunk.old_count++;
     ++	if (line[0] == ' ' || line[0] == '+')
     ++		filter->accumulating_hunk.lno_in_postimage++;
     ++	if (line[0] == ' ' || line[0] == '-')
     ++		filter->accumulating_hunk.lno_in_preimage++;
       
       	return filter->ret;
       }
      @@ diff.c: static void builtin_diff(const char *name_a,
       			lr_state.orig_cb_data = &ecbdata;
     - 			lr_state.ranges = line_ranges;
     - 			strbuf_init(&lr_state.hunk.lines, 0);
     + 			lr_state.range_sets_to_filter_by = line_ranges;
     + 			strbuf_init(&lr_state.accumulating_hunk.lines, 0);
      -			strbuf_init(&lr_state.pending_rm, 0);
       
       			/*
     @@ diff.c: static void builtin_diff(const char *name_a,
      @@ diff.c: static void builtin_diff(const char *name_a,
       				die("unable to generate diff for %s",
       				    one->path);
     - 			strbuf_release(&lr_state.hunk.lines);
     + 			strbuf_release(&lr_state.accumulating_hunk.lines);
      -			strbuf_release(&lr_state.pending_rm);
       		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
       					 &ecbdata, &xpp, &xecfg))
     @@ diff.c: static void builtin_diff(const char *name_a,
      
       ## t/t4211-line-log.sh ##
      @@ t/t4211-line-log.sh: test_expect_success '-L with -G filters to diff-text matches' '
     - 	grep "F2 + 2" actual
     + 	test_grep "F2 + 2" actual
       '
       
      +test_expect_success 'setup for trailing deletion test' '
     @@ t/t4211-line-log.sh: test_expect_success '-L with -G filters to diff-text matche
      +	{
      +	    return 1;
      +	}
     -+	// trailing comment
     ++	// trailing comment outside tracked range
      +	EOF
      +	git add file.c &&
      +	test_tick &&
      +	git commit -m "add file with trailing comment" &&
     -+	# Modify tracked() AND delete the trailing comment in
     -+	# one commit, so the commit touches the tracked range
     -+	# and is not filtered out by the revision walker.
     ++	# Remove the trailing comment AND modify tracked() so there
     ++	# is a modification to the line range we track and a
     ++	# modification to the following line, which we do not track.
      +	cat >file.c <<-\EOF &&
      +	void tracked()
      +	{
     @@ t/t4211-line-log.sh: test_expect_success '-L with -G filters to diff-text matche
      +
      +test_expect_success '-L does not include deletions past end of tracked range' '
      +	git log -L:tracked:file.c --format= -1 -p >actual &&
     -+	# The trailing comment deletion is outside the tracked
     -+	# range and should not appear in the patch output.
      +	test_grep "return 2" actual &&
      +	test_grep ! "trailing comment" actual
      +'
     -+
     -+test_expect_success '-L includes leading deletions resolved by in-range line' '
     -+	git checkout --orphan leading-del &&
     -+	git reset --hard &&
     -+	cat >file.c <<-\EOF &&
     -+	// leading comment
     -+	void tracked()
     -+	{
     -+	    return 1;
     -+	}
     -+	EOF
     -+	git add file.c &&
     -+	test_tick &&
     -+	git commit -m "add file with leading comment" &&
     -+	cat >file.c <<-\EOF &&
     -+	void tracked()
     -+	{
     -+	    return 2;
     -+	}
     -+	EOF
     -+	git commit -a -m "modify tracked and delete leading comment" &&
     -+	git log -L:tracked:file.c --format= -1 -p >actual &&
     -+	# The leading comment deletion is resolved by the next
     -+	# non-removal line (void tracked), which is in range: a
     -+	# removal is classified by the position of the following
     -+	# line, so it joins the range that line falls in.
     -+	test_grep "return 2" actual &&
     -+	test_grep "leading comment" actual
     -+'
     -+
     -+test_expect_success 'setup for line-range filter edge cases' '
     -+	git checkout --orphan filter-edge &&
     -+	git reset --hard &&
     -+	cat >file.c <<-\EOF &&
     -+	void before()
     -+	{
     -+	    return 0;
     -+	}
     -+
     -+	void tracked()
     -+	{
     -+	    int a = 1;
     -+	    int b = 2;
     -+	    int c = 3;
     -+	    return a + b + c;
     -+	}
     -+
     -+	void after()
     -+	{
     -+	    return 9;
     -+	}
     -+	EOF
     -+	git add file.c &&
     -+	test_tick &&
     -+	git commit -m "initial"
     -+'
     -+
     -+test_expect_success '-L change at exact first line of range' '
     -+	git checkout filter-edge &&
     -+	# Change the function signature (first line of range)
     -+	sed "s/void tracked/int tracked/" file.c >tmp &&
     -+	mv tmp file.c &&
     -+	git commit -a -m "change first line" &&
     -+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
     -+	test_grep "change first line" actual &&
     -+	test_grep "+int tracked" actual &&
     -+	test_grep "\\-void tracked" actual
     -+'
     -+
     -+test_expect_success '-L change at exact last line of range' '
     -+	git checkout filter-edge &&
     -+	git reset --hard HEAD~1 &&
     -+	# Change the closing brace line (last line of range)
     -+	sed "s/^}$/} \/\/ end tracked/" file.c >tmp &&
     -+	mv tmp file.c &&
     -+	git commit -a -m "change last line" &&
     -+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
     -+	test_grep "change last line" actual &&
     -+	test_grep "end tracked" actual
     -+'
     -+
     -+test_expect_success '-L pure deletion in range (no additions)' '
     -+	git checkout filter-edge &&
     -+	git reset --hard HEAD~1 &&
     -+	# Delete a line inside tracked() without adding anything
     -+	sed "/int c/d" file.c >tmp &&
     -+	mv tmp file.c &&
     -+	git commit -a -m "pure deletion" &&
     -+	git log -L:tracked:file.c -p --format=%s -1 >actual &&
     -+	test_grep "pure deletion" actual &&
     -+	test_grep "\\-.*int c" actual
     -+'
      +
       test_expect_success '-L with --diff-filter=M excludes root commit' '
       	git checkout parent-oids &&
 3:  d211c82e40 ! 3:  2081d5d257 diff: emit -L hunk headers via xdiff's formatter
     @@ Metadata
       ## Commit message ##
          diff: emit -L hunk headers via xdiff's formatter
      
     -    The line-range filter builds its own "@@ -<old> +<new> @@" header for
     -    each range hunk.  For a side with no lines (count 0, such as the old
     -    side of a pure insertion), the begin should be the number of the line
     -    before the change, per the convention git diff and xdl_emit_hunk_hdr()
     -    follow.  The hand-rolled code's begin was one too high; in t4211 this
     -    produced
     +    Currently, diff's line-range filter implements its own method for
     +    emitting diff hunk headers. This mostly matches what xdiff itself
     +    outputs, but there is a discrepancy for postimage or preimage sides
     +    with 0 line changes. For a side with no lines (count 0), the begin is
     +    the line before the change. The header omits the line count of 1.
      
     -            @@ -25,0 +18,9 @@
     +    Rather than fix this case in the line-range implementation, expose the
     +    function xdiff uses to emit its headers. Reusing it keeps the header
     +    format consistent with and without -L.
      
     -    an old begin of 25 in a 24-line file, where git diff would give 24.
     -
     -    Stop hand-rolling the header.  flush_range_hunk() now formats it through
     -    xdiff's own emitter: a new xdiff_emit_hunk_header() helper wraps
     -    xdl_emit_hunk_hdr(), the function that produces every other diff's hunk
     -    headers.  The count-0 begin is then correct by construction, and as a
     -    side effect -L headers match git diff exactly, including its omission of
     -    a count of 1 ("@@ -22 +22 @@" rather than "@@ -22,1 +22,1 @@").
     -
     -    xdiff's hunk callback already hands line_range_hunk_fn() a count-0 begin
     -    decremented, so undo that when seeding the cursors and let the formatter
     -    re-apply the convention once, at emit time.
     -
     -    The off-by-one predates this series, and the two regenerated fixtures
     -    reach it from different origins: no-assertion-error has carried it since
     -    its test was added in ab60c693a2 (line-log: fix assertion error,
     -    2025-08-18), while vanishes-early acquired it when 86e986f166 (line-log:
     -    route -L output through the standard diff pipeline) reshaped its tracked
     -    line into a pure insertion.  vanishes-early also drops its count-1
     -    counts.
     +    Update test scenarios and fixtures to reflect the now consistent header
     +    format.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
     @@ diff.c: static void flush_range_hunk(struct line_range_filter *filter)
       	}
       
      -	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
     --		    filter->hunk.old_begin, old_count,
     --		    filter->hunk.new_begin, new_count);
     --	if (filter->funclen > 0) {
     +-		    filter->accumulating_hunk.old_begin, old_count,
     +-		    filter->accumulating_hunk.new_begin, new_count);
     +-	if (filter->accumulating_hunk.func_name_len > 0) {
      -		strbuf_addch(&hdr, ' ');
     --		strbuf_add(&hdr, filter->func, filter->funclen);
     +-		strbuf_add(&hdr, filter->accumulating_hunk.func_name,
     +-			   filter->accumulating_hunk.func_name_len);
      -	}
      -	strbuf_addch(&hdr, '\n');
     -+	xdiff_emit_hunk_header(&hdr, filter->hunk.old_begin, old_count,
     -+			       filter->hunk.new_begin, new_count,
     -+			       filter->func, filter->funclen);
     ++	xdiff_emit_hunk_header(&hdr, filter->accumulating_hunk.old_begin, old_count,
     ++			       filter->accumulating_hunk.new_begin, new_count,
     ++			       filter->accumulating_hunk.func_name,
     ++			filter->accumulating_hunk.func_name_len);
       
       	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
       	strbuf_release(&hdr);
     @@ diff.c: static void flush_range_hunk(struct line_range_filter *filter)
       {
       	struct line_range_filter *filter = data;
       
     - 	/*
     --	 * When count > 0, begin is 1-based.  When count == 0, begin is
     --	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
     --	 * that type will arrive, so the value is unused.
     -+	 * Seed the per-image line cursors from the hunk header's begins.  For
     -+	 * a side with no lines (count 0), xdiff's callback has already moved
     -+	 * its begin to the line before the change, so add one back to recover
     -+	 * the true 1-based start.  xdiff_emit_hunk_header() reapplies that -1
     -+	 * when the clipped hunk is emitted.
     - 	 */
     --	filter->lno_in_postimage = new_begin;
     --	filter->lno_in_preimage = old_begin;
     -+	filter->lno_in_postimage = new_nr ? new_begin : new_begin + 1;
     -+	filter->lno_in_preimage = old_nr ? old_begin : old_begin + 1;
     +-	filter->accumulating_hunk.lno_in_postimage = new_begin;
     +-	filter->accumulating_hunk.lno_in_preimage = old_begin;
     ++	filter->accumulating_hunk.lno_in_postimage = new_nr ? new_begin : new_begin + 1;
     ++	filter->accumulating_hunk.lno_in_preimage = old_nr ? old_begin : old_begin + 1;
       
       	if (funclen > 0) {
     - 		if (funclen > (long)sizeof(filter->func))
     + 		if (funclen > (long)sizeof(filter->accumulating_hunk.func_name))
      
       ## t/t4211/sha1/expect.no-assertion-error ##
      @@ t/t4211/sha1/expect.no-assertion-error: diff --git a/b.c b/b.c
     @@ xdiff-interface.h: int xdiff_compare_lines(const char *l1, long s1,
      +
      +/*
      + * Append a unified-diff hunk header to `out`, e.g.
     -+ * "@@ -<old> +<new> @@ func\n".  The header comes from wrapping xdiff's
     ++ * "@@ -<old> +<new> @@ func\n". The header comes from wrapping xdiff's
      + * own hunk-header emitter, so it matches what a normal diff would
     -+ * produce for these begins and counts.  For a side with no lines
     -+ * (count 0) the begin is the line before the change, and a count of 1
     -+ * is omitted.
     ++ * produce for the given line number begins and line counts.
      + */
      +void xdiff_emit_hunk_header(struct strbuf *out,
     -+			    long old_begin, long old_count,
     -+			    long new_begin, long new_count,
     ++			    long old_begin, long old_nr,
     ++			    long new_begin, long new_nr,
      +			    const char *func, long funclen);
      +
       #endif
 4:  b82a997359 ! 4:  6b13c13ae7 diff: extract a line-range diff helper for reuse
     @@ Metadata
       ## Commit message ##
          diff: extract a line-range diff helper for reuse
      
     -    builtin_diff() open-codes the line-range filter setup and teardown
     -    around its xdi_diff_outf() call: zero the struct, point it at the
     -    output callback, inflate ctxlen to the largest range span so each range
     -    yields a single xdiff hunk, run the diff, flush the trailing range
     -    hunk, and release the buffer.  The upcoming -L stat and check formats
     -    need the same sequence.
     +    Extract logic for initializing the line-range filter and running a diff
     +    for a specific line range. This logic is needed for any diff that
     +    targets a line range independent of the current patch display path.
      
     -    Extract line_range_filter_init() for the setup and a
     -    line_range_filter_diff() helper that prepares the xdiff config the
     -    filter needs, runs an initialized filter through xdi_diff_outf(),
     -    flushes the final range hunk, and releases it, returning the latched
     -    error.  The helper inflates ctxlen to the largest range span so each
     -    range yields a single xdiff hunk, and clears XDL_EMIT_NO_HUNK_HDR so
     -    the hunk headers the filter seeds its position from are always emitted.
     -    Folding both into the helper keeps these invariants, which the filter's
     -    position tracking relies on, in a single place for every consumer.
     -    builtin_diff() now does init + line_range_filter_diff(); the next two
     -    patches reuse them in builtin_diffstat() and builtin_checkdiff()
     -    instead of repeating the boilerplate.
     +    The subsequent commits use this logic to enable additional line range
     +    targeted diff modes.
      
     -    No behavior change: builtin_diff() leaves XDL_EMIT_NO_HUNK_HDR unset,
     -    so clearing it is a no-op until the suppressing consumers arrive.
     +    No logical behavior change.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
     @@ diff.c: static int quick_consume(void *priv, char *line UNUSED, unsigned long le
      +	memset(filter, 0, sizeof(*filter));
      +	filter->orig_line_fn = line_fn;
      +	filter->orig_cb_data = cb_data;
     -+	filter->ranges = ranges;
     -+	strbuf_init(&filter->hunk.lines, 0);
     ++	filter->range_sets_to_filter_by = ranges;
     ++	strbuf_init(&filter->accumulating_hunk.lines, 0);
      +}
      +
     - /*
     -  * Begin a range hunk at the first in-range line.  Its position fixes the
     -  * hunk's begins, taken from the two image cursors before they advance:
     + static void begin_range_hunk(struct line_range_filter *filter)
     + {
     + 	filter->accumulating_hunk.active = 1;
      @@ diff.c: static int line_range_line_fn(void *priv, char *line, unsigned long len)
       	return filter->ret;
       }
       
     -+/*
     -+ * Run an xdiff pass through an initialized line-range filter, flush the
     -+ * final range hunk, and release the filter.  Inflates ctxlen to the largest
     -+ * range span first, so that every change within a single range lands in one
     -+ * xdiff hunk and the inter-change context is emitted; the filter then clips
     -+ * back to range boundaries.  The optimal ctxlen depends on where changes fall
     -+ * within the range, which is only known after xdiff runs, so the max span is
     -+ * the upper bound that guarantees correctness in a single pass.  Every
     -+ * consumer (patch, diffstat, check) relies on one xdiff hunk per range, so
     -+ * this lives here rather than at each call site.  Also clears
     -+ * XDL_EMIT_NO_HUNK_HDR: the filter seeds its per-image position from the hunk
     -+ * headers, so a consumer that otherwise suppresses them (diffstat) still gets
     -+ * them here.  Returns non-zero if xdiff or any forwarded callback failed.
     -+ */
     ++
      +static int line_range_filter_diff(struct line_range_filter *filter,
      +				  mmfile_t *mf1, mmfile_t *mf2,
      +				  xpparam_t *xpp, xdemitconf_t *xecfg)
      +{
     -+	const struct range_set *ranges = filter->ranges;
     ++	const struct range_set *ranges = filter->range_sets_to_filter_by;
      +	long max_span = 0;
      +	unsigned int i;
      +	int ret;
     @@ diff.c: static int line_range_line_fn(void *priv, char *line, unsigned long len)
      +		flush_range_hunk(filter);
      +		ret = filter->ret;
      +	}
     -+	strbuf_release(&filter->hunk.lines);
     ++	strbuf_release(&filter->accumulating_hunk.lines);
      +	return ret;
      +}
      +
     @@ diff.c: static void builtin_diff(const char *name_a,
      -			memset(&lr_state, 0, sizeof(lr_state));
      -			lr_state.orig_line_fn = fn_out_consume;
      -			lr_state.orig_cb_data = &ecbdata;
     --			lr_state.ranges = line_ranges;
     --			strbuf_init(&lr_state.hunk.lines, 0);
     +-			lr_state.range_sets_to_filter_by = line_ranges;
     +-			strbuf_init(&lr_state.accumulating_hunk.lines, 0);
      -
      -			/*
      -			 * Inflate ctxlen so that all changes within
     @@ diff.c: static void builtin_diff(const char *name_a,
      +						   &xpp, &xecfg))
       				die("unable to generate diff for %s",
       				    one->path);
     --			strbuf_release(&lr_state.hunk.lines);
     +-			strbuf_release(&lr_state.accumulating_hunk.lines);
       		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
       					 &ecbdata, &xpp, &xecfg))
       			die("unable to generate diff for %s", one->path);
 5:  3d0091b549 ! 5:  f12b61b9a4 line-log: support diff stat formats with -L
     @@ Metadata
      Author: Michael Montalbo <mmontalbo@gmail.com>
      
       ## Commit message ##
     -    line-log: support diff stat formats with -L
     +    diff: support stat formats with -L
      
     -    Reuse the line_range_filter in builtin_diffstat() so the stat formats
     -    count only the lines within the tracked range.  When a filepair carries
     -    line_ranges, the filter wraps diffstat_consume() as its output callback,
     -    forwarding only the lines inside the range for counting.
     -    flush_range_hunk() replays buffered content through diffstat_consume(),
     -    which ignores synthetic @@ headers since it only counts '+' and '-'
     -    lines.
     +    Reuse the line_range_filter in builtin_diffstat() so -L supports
     +    the stat formats and add tests verifying the new behavior.
      
     -    Expand the output format allowlist in setup_revisions() to accept
     -    --stat, --numstat, and --shortstat with -L.
     -
     -    Leave --dirstat out of the allowlist so it is rejected like any other
     -    unsupported format.  Its default mode counts each file's whole-file
     -    byte damage via diffcore_count_changes(), outside the line-based
     -    pipeline that the -L filter scopes, so bare --dirstat cannot honor the
     -    tracked range.  The --dirstat=lines mode could: it aggregates the same
     -    per-file line counts as --numstat, which -L already scopes.  But
     -    accepting only that sub-mode while bare --dirstat keeps erroring is a
     -    confusing split, so the whole format is deferred to a follow-up;
     -    --numstat already reports the exact per-file counts within the tracked
     -    range.
     -
     -    Also drop "yet" from the generic -L rejection message ("does not
     -    yet support the requested diff format").  Some rejected formats do
     -    not fit a line range at all, so "yet" wrongly implied they are all
     -    just awaiting support.
     +    Ungate the newly enabled options and drop "yet" from the generic
     +    -L rejection message ("does not yet support the requested diff
     +    format"). Some rejected formats do not fit -L at all, so "yet"
     +    wrongly implies they are all awaiting support.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
     @@ Documentation/line-range-options.adoc
      -	(`--stat`, `--numstat`, `--shortstat`, `--dirstat`) are not
      -	currently implemented.
      +	The following non-patch diff formats are supported: `--raw`,
     -+	`--name-only`, `--name-status`, `--summary`,
     -+	`--stat`, `--numstat`, and `--shortstat`.
     -+	The stat formats count only lines within the tracked range.
     -+	`--dirstat` is not supported
     -+	with `-L`: it summarizes change as each directory's share of
     -+	the total churn, not as counts for the tracked lines.  Use
     -+	`--numstat` for exact per-file counts within the range.
     ++	`--name-only`, `--name-status`, `--summary`, `--stat`, `--numstat`,
     ++	and `--shortstat`. The stat formats count only lines within the tracked
     ++	range. `--dirstat` is not supported with `-L`: it summarizes change as each
     ++	directory's share of the total churn, not as counts for the tracked lines.
     ++	Use `--numstat` for exact per-file counts within the range.
       +
       Patch formatting options such as `--word-diff`, `--color-moved`,
       `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
     @@ t/t4211-line-log.sh: test_expect_success '--name-status shows status and path' '
      -
      -test_expect_success '--dirstat is not yet supported with -L' '
      +test_expect_success '--dirstat is not supported with -L' '
     -+	# --dirstat is not supported with -L: its default mode measures
     -+	# whole-file change, not the tracked lines, and the
     -+	# --dirstat=lines variant is deferred too, so both forms are
     -+	# rejected like any other unsupported format.
       	test_must_fail git log -L1,24:b.c --dirstat 2>err &&
      -	test_grep "does not yet support" err
     -+	test_grep "does not support" err &&
     -+	test_must_fail git log -L1,24:b.c --dirstat=lines 2>err &&
      +	test_grep "does not support" err
       '
       
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
       	test_grep "^diff --git" line2
       '
       
     -+test_expect_success 'setup for stat range-scoping tests' '
     -+	git checkout --orphan stat-scoping &&
     ++test_expect_success 'setup for -L stat tests' '
     ++	git checkout --orphan stat-range &&
      +	git reset --hard &&
      +	cat >file.c <<-\EOF &&
      +	int func1()
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +	    return F1;
      +	}
      +
     -+	int func2()
     ++	int tracked_fn()
      +	{
      +	    return F2;
      +	}
      +	EOF
      +	git add file.c &&
      +	test_tick &&
     -+	git commit -m "Add func1() and func2()" &&
     ++	git commit -m "Add func1() and tracked_fn()" &&
      +
     -+	# Modify both functions in a single commit so that
     -+	# whole-file stats differ from the counts for the tracked range.
     ++	# Modify both functions so whole-file stats (2 added, 2 deleted)
     ++	# differ from the tracked range of tracked_fn (1 and 1).
      +	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" file.c >tmp &&
      +	mv tmp file.c &&
      +	git commit -a -m "Modify both functions"
      +'
      +
     -+test_expect_success '--numstat counts only lines in tracked range' '
     -+	# "Modify both functions" changes one line in func1 and one in
     -+	# func2.  Whole-file numstat would show 2 added, 2 deleted.
     -+	# numstat for func2 within the tracked range should show only 1 and 1.
     -+	git log -L:func2:file.c --numstat --format=%s -1 >actual &&
     -+	test_grep "Modify both functions" actual &&
     -+	test_grep "^1	1	file.c$" actual &&
     -+	test_grep ! "^diff --git" actual
     -+'
     ++test_expect_success '-L --numstat limits counts to the tracked range' '
     ++	git log -L:tracked_fn:file.c --numstat --format=%s >actual &&
     ++	cat >expect <<-\EOF &&
     ++	Modify both functions
      +
     -+test_expect_success '--numstat counts only additions for root commit' '
     -+	# Root commit creates both func1 (4 lines) and func2 (4 lines).
     -+	# Whole-file numstat would show 9 lines added.  numstat for func2
     -+	# within the tracked range should show only 4.
     -+	git log -L:func2:file.c --numstat --format=%s >actual &&
     -+	test_grep "Add func1() and func2()" actual &&
     -+	test_grep "^4	0	file.c$" actual &&
     -+	test_grep ! "^diff --git" actual
     -+'
     ++	1	1	file.c
     ++	Add func1() and tracked_fn()
      +
     -+test_expect_success '--stat counts only lines in tracked range' '
     -+	git log -L:func2:file.c --stat --format=%s -1 >actual &&
     -+	test_grep "Modify both functions" actual &&
     -+	test_grep "file.c |" actual &&
     -+	test_grep "1 insertion" actual &&
     -+	test_grep "1 deletion" actual &&
     -+	test_grep ! "^diff --git" actual
     ++	4	0	file.c
     ++	EOF
     ++	test_cmp expect actual
      +'
      +
     -+test_expect_success '--shortstat counts only lines in tracked range' '
     -+	# --shortstat prints only the summary line: no per-file "file.c |"
     -+	# line.  Counts cover only the tracked range, as for --numstat above.
     -+	git log -L:func2:file.c --shortstat --format=%s -1 >actual &&
     -+	test_grep "Modify both functions" actual &&
     -+	test_grep "1 insertion" actual &&
     -+	test_grep "1 deletion" actual &&
     -+	test_grep ! "file.c |" actual &&
     -+	test_grep ! "^diff --git" actual
     ++test_expect_success '-L --stat and --shortstat limit counts to the tracked range' '
     ++	git log -L:tracked_fn:file.c --stat --format=%s -1 >actual &&
     ++	cat >expect <<-\EOF &&
     ++	Modify both functions
     ++
     ++	 file.c | 2 +-
     ++	 1 file changed, 1 insertion(+), 1 deletion(-)
     ++	EOF
     ++	test_cmp expect actual &&
     ++
     ++	git log -L:tracked_fn:file.c --shortstat --format=%s -1 >actual &&
     ++	cat >expect <<-\EOF &&
     ++	Modify both functions
     ++
     ++	 1 file changed, 1 insertion(+), 1 deletion(-)
     ++	EOF
     ++	test_cmp expect actual
      +'
      +
      +test_expect_success '--numstat across renames and multiple commits' '
      +	# parallel-change carries the tracked function f across an a.c -> b.c
     -+	# rename and a merge of two parallel histories.  With -M, --numstat
     -+	# follows the rename and reports added/removed counts for f within
     -+	# the tracked range (not whole-file) per commit; the file column flips from
     -+	# b.c to a.c at the rename as the walk goes back in time.  Commits
     -+	# that do not change the range of f emit no row (the merge and the
     -+	# pure file-move produce nothing), so there are fewer rows than
     -+	# commits.
     ++	# rename and a merge of two parallel histories.
      +	git checkout parallel-change &&
      +	git log -M -L ":f:b.c" --format= --numstat >actual &&
      +	cat >expect <<-\EOF &&
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +	git checkout --orphan multi-range &&
      +	git reset --hard &&
      +	cat >m.c <<-\EOF &&
     -+	int func1()
     ++	int tracked_func1()
      +	{
      +	    return F1;
      +	}
      +
     -+	int func2()
     ++	int tracked_func2()
      +	{
      +	    return F2;
      +	}
     @@ t/t4211-line-log.sh: test_expect_success '-L --oneline has no extra blank line b
      +	git add m.c &&
      +	test_tick &&
      +	git commit -m "add m.c" &&
     -+	# Change all three functions but track only func1 and func2.
     -+	# Whole-file numstat would be 3 3; a 2 2 result proves the
     -+	# untracked func3 change is excluded and the two ranges just sum.
      +	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" -e "s/F3/F3 + 3/" m.c >tmp &&
      +	mv tmp m.c &&
      +	git commit -a -m "Modify all three functions" &&
     -+	git log -L:func1:m.c -L:func2:m.c --numstat --format=%s -1 >actual &&
     -+	test_grep "Modify all three functions" actual &&
     -+	test_grep "^2	2	m.c$" actual &&
     -+	test_grep ! "^3	3	m.c$" actual
     ++	git log -L:tracked_func1:m.c -L:tracked_func2:m.c --numstat --format=%s -1 >actual &&
     ++	cat >expect <<-\EOF &&
     ++	Modify all three functions
     ++
     ++	2	2	m.c
     ++	EOF
     ++	test_cmp expect actual
      +'
      +
       test_expect_success '--summary shows new file on root commit' '
 6:  36ed52d831 ! 6:  f1f5af8f77 diff: support --check with -L line ranges
     @@ Metadata
       ## Commit message ##
          diff: support --check with -L line ranges
      
     -    builtin_checkdiff() runs its own xdiff pass to detect whitespace
     -    errors in newly added lines.  When -L is active, the check should
     -    be scoped to the tracked line ranges rather than the whole file.
     +    Reuse the line_range_filter in builtin_checkdiff() so -L supports
     +    the --check option.
      
     -    Reuse the line_range_filter to wrap checkdiff_consume(), the same
     -    pattern already used for patch output and diffstat.  The filter
     -    forwards only in-range lines for whitespace checking.
     +    Add orig_hunk_fn field similar to orig_line_fn that forwards
     +    xdiff_emit_hunk_fn calls when we flush filtered hunks. This is necessary
     +    because --check relies on receiving calls to its checkdiff_consume_hunk
     +    function for managing state.
      
     -    checkdiff reports the file line number of each error, which it
     -    normally learns from the hunk header via checkdiff_consume_hunk().
     -    The filter synthesizes its own hunk headers, so give it an optional
     -    hunk callback and route checkdiff_consume_hunk() through it; this
     -    sets the post-image position before the in-range lines are replayed.
     -    Without it the reported line numbers would count from the start of
     -    the range hunk rather than the start of the file.
     -
     -    The trailing blank-at-eof check is a second pass that scans the whole
     -    file via check_blank_at_eof(), so gate its report on the tracked
     -    ranges as well; otherwise a blank line added at end of file is
     -    reported even when it lies outside the range.
     -
     -    Add DIFF_FORMAT_CHECKDIFF to the -L output format allowlist in
     -    setup_revisions() so that -L --check is accepted, and list --check
     -    among the supported formats in the documentation.  Add tests covering
     -    that whitespace errors are reported, scoped to the tracked range, and
     -    labeled with the correct file line number, including when two errors
     -    in one range are separated by a gap that would otherwise split into
     -    multiple xdiff hunks.
     +    Document and ungate the newly enabled option, and add tests verifying
     +    the new behavior.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
     @@ Documentation/line-range-options.adoc
       	You can specify this option more than once. Implies `--patch`.
       	Patch output can be suppressed using `--no-patch`.
       	The following non-patch diff formats are supported: `--raw`,
     --	`--name-only`, `--name-status`, `--summary`,
     -+	`--name-only`, `--name-status`, `--summary`, `--check`,
     - 	`--stat`, `--numstat`, and `--shortstat`.
     - 	The stat formats count only lines within the tracked range.
     - 	`--dirstat` is not supported
     +-	`--name-only`, `--name-status`, `--summary`, `--stat`, `--numstat`,
     +-	and `--shortstat`. The stat formats count only lines within the tracked
     +-	range. `--dirstat` is not supported with `-L`: it summarizes change as each
     +-	directory's share of the total churn, not as counts for the tracked lines.
     +-	Use `--numstat` for exact per-file counts within the range.
     ++	`--name-only`, `--name-status`, `--summary`, `--check`, `--stat`,
     ++	`--numstat`, and `--shortstat`. The stat formats count only lines
     ++	within the tracked range. `--dirstat` is not supported with `-L`: it
     ++	reports how change is distributed across directories over whole files,
     ++	which is not meaningful for line ranges within a file. Use `--numstat`
     ++	for exact per-file counts within the range.
     + +
     + Patch formatting options such as `--word-diff`, `--color-moved`,
     + `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
      
       ## diff.c ##
      @@ diff.c: struct emit_callback {
        */
       struct line_range_filter {
       	xdiff_emit_line_fn orig_line_fn;
     -+	/*
     -+	 * Optional; consumers that report file line numbers (e.g.
     -+	 * checkdiff) need the synthetic hunk header to set their
     -+	 * post-image position before in-range lines are replayed.
     -+	 */
      +	xdiff_emit_hunk_fn orig_hunk_fn;
       	void *orig_cb_data;
     - 	const struct range_set *ranges;	/* 0-based [start, end) */
     - 	unsigned int cur_range;		/* index into the range_set */
     + 	const struct range_set *range_sets_to_filter_by;
     + 	unsigned int range_set_idx;
      @@ diff.c: static void flush_range_hunk(struct line_range_filter *filter)
     - 			       filter->hunk.new_begin, new_count,
     - 			       filter->func, filter->funclen);
     + 			       filter->accumulating_hunk.func_name,
     + 			filter->accumulating_hunk.func_name_len);
       
     -+	/*
     -+	 * Inform a line-numbering consumer of the post-image position
     -+	 * before replaying lines, mirroring the hunk callback xdiff
     -+	 * would have issued for a non-scoped diff.
     -+	 */
      +	if (filter->orig_hunk_fn)
      +		filter->orig_hunk_fn(filter->orig_cb_data,
     -+				filter->hunk.old_begin, old_count,
     -+				filter->hunk.new_begin, new_count,
     -+				filter->func, filter->funclen);
     ++				filter->accumulating_hunk.old_begin, old_count,
     ++				filter->accumulating_hunk.new_begin, new_count,
     ++				filter->accumulating_hunk.func_name,
     ++		       filter->accumulating_hunk.func_name_len);
      +
       	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
       	strbuf_release(&hdr);
     @@ diff.c: static void builtin_diffstat(const char *name_a, const char *name_b,
       	diff_free_filespec_data(two);
       }
       
     -+/*
     -+ * Is the 0-based line index within any of the tracked ranges?
     -+ * (range_set ranges are 0-based, half-open [start, end).)  This is a
     -+ * one-shot query for a single line and scans; the streaming filter
     -+ * (line_range_line_fn) uses a forward cursor instead.
     -+ */
      +static int idx_in_ranges(const struct range_set *ranges, long idx)
      +{
      +	unsigned int i;
     @@ diff.c: static void builtin_checkdiff(const char *name_a, const char *name_b,
       			check_blank_at_eof(&mf1, &mf2, &ecbdata);
       			blank_at_eof = ecbdata.blank_at_eof_in_postimage;
       
     -+			/*
     -+			 * check_blank_at_eof() scans the whole file; with -L,
     -+			 * keep the report only when its line is in a tracked
     -+			 * range.  The error's location is the first trailing
     -+			 * blank line (blank_at_eof, 1-based; ranges 0-based), so
     -+			 * we scope by that line.
     -+			 */
      +			if (blank_at_eof && line_ranges &&
      +			    !idx_in_ranges(line_ranges, blank_at_eof - 1))
      +				blank_at_eof = 0;
     @@ revision.c: int setup_revisions(int argc, const char **argv, struct rev_info *re
       	if (revs->expand_tabs_in_log < 0)
      
       ## t/t4211-line-log.sh ##
     -@@ t/t4211-line-log.sh: test_expect_success '--summary shows new file on root commit' '
     - 	test_grep "create mode 100644 file.c" actual
     +@@ t/t4211-line-log.sh: test_expect_success 'get_commit_action() does not mutate a not-yet-walked commit
     + 	)
       '
       
      +test_expect_success 'setup for --check test' '
     @@ t/t4211-line-log.sh: test_expect_success '--summary shows new file on root commi
      +	git add check.c &&
      +	test_tick &&
      +	git commit -m "add check.c" &&
     -+	# Introduce trailing whitespace errors in both functions
      +	sed "s/return;/return; /" check.c >check.c.tmp &&
      +	mv check.c.tmp check.c &&
      +	git commit -a -m "introduce trailing whitespace"
      +'
      +
     -+test_expect_success '--check scoped to tracked range with correct file line' '
     -+	# tracked() trailing whitespace is at check.c:3; report it with the
     -+	# real file line number, not a count from the start of the range
     -+	# hunk.  other() at check.c:8 is outside the range and is excluded.
     -+	test_must_fail git log -L:tracked:check.c --check --format= >actual &&
     -+	test_grep "check.c:3: trailing whitespace" actual &&
     -+	test_grep ! "check.c:8:" actual
     -+'
     ++test_expect_success '--check is limited to tracked ranges and reports real file line numbers' '
     ++	test_must_fail git log -L:tracked:check.c --check --format= >raw &&
     ++	grep -E ":[0-9]+:" raw >actual &&
     ++	echo "check.c:3: trailing whitespace." >expect &&
     ++	test_cmp expect actual &&
      +
     -+test_expect_success '--check reports each of several tracked ranges' '
     -+	# Track both functions as separate ranges.  Each range is flushed
     -+	# as its own hunk, so the second error must report its real file
     -+	# line (check.c:8), not continue the numbering from the first
     -+	# range (check.c:3).
      +	test_must_fail git log -L:tracked:check.c -L:other:check.c \
     -+		--check --format= >actual &&
     -+	test_grep "check.c:3: trailing whitespace" actual &&
     -+	test_grep "check.c:8: trailing whitespace" actual
     ++		--check --format= >raw &&
     ++	grep -E ":[0-9]+:" raw >actual &&
     ++	cat >expect <<-\EOF &&
     ++	check.c:3: trailing whitespace.
     ++	check.c:8: trailing whitespace.
     ++	EOF
     ++	test_cmp expect actual
      +'
      +
     -+test_expect_success '--check line numbers stay correct across a gap in one range' '
     ++test_expect_success '--check reports each error at its real line across a gap in one range' '
      +	git checkout --orphan check-gap &&
      +	git reset --hard &&
      +	cat >gap.c <<-\EOF &&
     @@ t/t4211-line-log.sh: test_expect_success '--summary shows new file on root commi
      +	git add gap.c &&
      +	test_tick &&
      +	git commit -m "add gap.c" &&
     -+	# Two trailing-whitespace errors within one tracked range,
     -+	# separated by clean lines.  ctxlen is inflated to the range span,
     -+	# so they land in a single xdiff hunk with the gap as context;
     -+	# both must report their real file line number, with the context
     -+	# lines between them counted.
      +	sed -e "s/int a = 1;/int a = 1; /" -e "s/int g = 7;/int g = 7; /" gap.c >tmp &&
      +	mv tmp gap.c &&
      +	git commit -a -m "ws errors with a gap" &&
     -+	test_must_fail git log -L:tracked:gap.c --check --format= >actual &&
     -+	test_grep "gap.c:3: trailing whitespace" actual &&
     -+	test_grep "gap.c:8: trailing whitespace" actual
     ++	test_must_fail git log -L:tracked:gap.c --check --format= >raw &&
     ++	grep -E ":[0-9]+:" raw >actual &&
     ++	cat >expect <<-\EOF &&
     ++	gap.c:3: trailing whitespace.
     ++	gap.c:8: trailing whitespace.
     ++	EOF
     ++	test_cmp expect actual
      +'
      +
      +test_expect_success '--check does not report blank-at-eof outside the range' '
     @@ t/t4211-line-log.sh: test_expect_success '--summary shows new file on root commi
      +	git add eof.c &&
      +	test_tick &&
      +	git commit -m "add eof.c" &&
     -+	# One commit introduces a trailing-whitespace error inside tracked()
     -+	# (line 3) and a blank line at end of file (line 7, outside the
     -+	# range).  The blank-at-eof check scans the whole file, so it must be
     -+	# scoped: report the in-range error, not the out-of-range EOF blank.
      +	printf "void tracked()\n{\n    return; \n}\n\nint tail = 1;\n\n" >eof.c &&
      +	git commit -a -m "ws in range, blank at eof out of range" &&
     -+	test_must_fail git log -L:tracked:eof.c --check --format= >actual &&
     -+	test_grep "eof.c:3: trailing whitespace" actual &&
     -+	test_grep ! "blank line at EOF" actual
     ++	test_must_fail git log -L:tracked:eof.c --check --format= >raw &&
     ++	grep -E ":[0-9]+:" raw >actual &&
     ++	echo "eof.c:3: trailing whitespace." >expect &&
     ++	test_cmp expect actual
      +'
      +
       test_done
 7:  df83e6275b ! 7:  cff5c124ec diffcore-pickaxe: scope -G to the -L tracked range
     @@ Metadata
      Author: Michael Montalbo <mmontalbo@gmail.com>
      
       ## Commit message ##
     -    diffcore-pickaxe: scope -G to the -L tracked range
     +    diffcore-pickaxe: limit -G to the -L tracked range
      
     -    git log -L scopes its diff output to the tracked range, but pickaxe
     -    (-S, -G) still runs in diffcore over the whole-file change, so -L -G
     -    selects a commit whenever the pattern appears in any added or removed
     -    line of the file, even outside the tracked range.
     +    Teach -G to only search the line ranges specified by -L.
     +    Teaching -S is left as future work, so it still matches the entire
     +    file even if -L is specified.
      
     -    Teach -G to honor the range.  diff_grep() already runs an xdiff pass
     -    and greps the +/- lines; route that pass through the line-range filter
     -    so only the tracked range's lines are grepped.  Expose the filter as
     -    diff_emit_line_ranges(), an xdi_diff_outf() that emits only the tracked
     -    range's lines, thread the filepair's line_ranges through the pickaxe
     -    callback, and pass it from pickaxe_match().  Skip scoping under
     -    textconv, whose output is not in the original file's line coordinates.
     +    Rather than being part of diff.c's builtin implementations, the
     +    diffcore-pickaxe functionality interacts with xdiff-interface as a
     +    separate component. Add a sibling to xdi_diff_outf(), called
     +    diff_emit_line_ranges(), that limits emitted lines to the given line
     +    ranges.
      
     -    -G needs only a hit/no-hit answer, so the line-number concerns the
     -    filter handles for patch and check output do not apply here.
     +    Use diff_emit_line_ranges() when searching text if line ranges have
     +    been specified. If textconv is enabled, use normal diffing instead of
     +    diff_emit_line_ranges() since line range tracking relies on the line
     +    coordinates of the original, pre-textconv file.
      
     -    -S is left matching the whole file: it counts needle occurrences per
     -    blob rather than grepping the diff, so scoping it needs a different
     -    approach, left to a follow-up.  has_changes() takes the range parameter
     -    but ignores it for now.
     -
     -    Document the resulting -L pickaxe scoping: -G is scoped to the tracked
     -    range, while -S still matches the whole file.
     +    Update documentation and add tests accordingly.
      
          Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
      
     @@ Documentation/line-range-options.adoc
       Patch formatting options such as `--word-diff`, `--color-moved`,
       `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
      -as are pickaxe options (`-S`, `-G`) and `--diff-filter`.
     -+as are pickaxe options (`-S`, `-G`) and `--diff-filter`.  `-G` is
     -+scoped to the tracked range; `-S` is still evaluated over the whole
     -+file, so an `-S` query may select a commit for a change outside the
     -+range.
     ++as are pickaxe options (`-S`, `-G`) and `--diff-filter`. `-G` is
     ++limited to the tracked range. In contrast, `-S` is evaluated over the whole
     ++file and may select a commit with a change outside the tracked range.
       +
       include::line-range-format.adoc[]
      
     @@ diff.c: static int line_range_filter_diff(struct line_range_filter *filter,
       	return ret;
       }
       
     -+/*
     -+ * Expose the in-file line-range filter to callers outside diff.c (e.g.
     -+ * pickaxe -G); see xdiff-interface.h for the contract.
     -+ */
      +int diff_emit_line_ranges(mmfile_t *one, mmfile_t *two,
      +			  const struct range_set *ranges,
      +			  xdiff_emit_line_fn line_fn, void *cb_data,
     @@ diffcore-pickaxe.c: static int diffgrep_consume(void *priv, char *line, unsigned
       {
       	struct diffgrep_cb ecbdata;
       	xpparam_t xpp;
     -@@ diffcore-pickaxe.c: static int diff_grep(mmfile_t *one, mmfile_t *two,
     - 	int ret;
     - 
     - 	/*
     --	 * We have both sides; need to run textual diff and see if
     --	 * the pattern appears on added/deleted lines.
     -+	 * We have both sides; need to run textual diff and see if the
     -+	 * pattern appears on added/deleted lines.  Under -L (ranges set),
     -+	 * forward only the tracked range's lines so the match is scoped.
     -+	 * -G needs only a hit/no-hit answer, so the line-number bookkeeping
     -+	 * the filter does for -L patch and check output is irrelevant here.
     - 	 */
     - 	memset(&xpp, 0, sizeof(xpp));
     - 	memset(&xecfg, 0, sizeof(xecfg));
      @@ diffcore-pickaxe.c: static int diff_grep(mmfile_t *one, mmfile_t *two,
       	 * An xdiff error might be our "data->hit" from above. See the
       	 * comment for xdiff_emit_line_fn in xdiff-interface.h
     @@ diffcore-pickaxe.c: static unsigned int contains(mmfile_t *mf, regex_t *regexp,
      +		       const struct range_set *ranges UNUSED)
       {
      +	/*
     -+	 * -S counts needle occurrences in each whole blob.  Scoping this to
     -+	 * a -L range is left to a follow-up; for now -S ignores the range.
     ++	 * -S counts needle occurrences in each whole blob. Limiting this to
     ++	 * an -L range is left as a follow-up; for now -S ignores the range.
      +	 */
       	unsigned int c1 = one ? contains(one, regexp, kws, 0) : 0;
       	unsigned int c2 = two ? contains(two, regexp, kws, c1 + 1) : 0;
     @@ diffcore-pickaxe.c: static int pickaxe_match(struct diff_filepair *p, struct dif
       
      -	ret = fn(&mf1, &mf2, o, regexp, kws);
      +	/*
     -+	 * -L scopes the search to the tracked range, but the range is in
     -+	 * original-file line coordinates that do not map onto textconv
     -+	 * output, so search the whole file when textconv is in play.
     ++	 * -L limits the search to the tracked range, but the range is in
     ++	 * pre-textconv line coordinates that do not map onto textconv
     ++	 * output, so search the whole file when textconv is enabled.
      +	 */
      +	ranges = (textconv_one || textconv_two) ? NULL : p->line_ranges;
      +	ret = fn(&mf1, &mf2, o, regexp, kws, ranges);
     @@ diffcore-pickaxe.c: static int pickaxe_match(struct diff_filepair *p, struct dif
       		free(mf1.ptr);
      
       ## t/t4211-line-log.sh ##
     -@@ t/t4211-line-log.sh: test_expect_success '-L with -S filters to string-count changes' '
     - test_expect_success '-L with -G filters to diff-text matches' '
     +@@ t/t4211-line-log.sh: test_expect_success '-L suppresses deletions outside tracked range' '
     + 	test $(grep -c "^diff --git" actual) = 1
     + '
     + 
     +-test_expect_success '-L with -S filters to string-count changes' '
     ++test_expect_success '-L with -S selects only the matching commit' '
     + 	git checkout parent-oids &&
     +-	git log -L:func2:file.c -S "F2 + 2" --format= >actual &&
     +-	# -S searches the whole file, not just the tracked range;
     +-	# combined with the -L range walk, this selects commits that
     +-	# both touch func2 and change the count of "F2 + 2" in the file.
     +-	test $(grep -c "^diff --git" actual) = 1 &&
     +-	test_grep "F2 + 2" actual
     ++	git log -L:func2:file.c -S "F2 + 2" --format=%s --no-patch >actual &&
     ++	echo "Modify func2() in file.c" >expect &&
     ++	test_cmp expect actual
     + '
     + 
     +-test_expect_success '-L with -G filters to diff-text matches' '
     ++test_expect_success '-L with -G selects only the matching commit' '
       	git checkout parent-oids &&
     - 	git log -L:func2:file.c -G "F2 [+] 2" --format= >actual &&
     +-	git log -L:func2:file.c -G "F2 [+] 2" --format= >actual &&
      -	# -G greps the whole-file diff text, not just the tracked range;
      -	# combined with -L, this selects commits that both touch func2
      -	# and have "F2 + 2" in their diff.
     -+	# -G greps the diff text, and under -L only the lines in the
     -+	# tracked range (unlike -S above, which searches the whole file);
     -+	# this selects commits whose change to func2 contains "F2 + 2".
     - 	test $(grep -c "^diff --git" actual) = 1 &&
     - 	grep "F2 + 2" actual
     +-	test $(grep -c "^diff --git" actual) = 1 &&
     +-	test_grep "F2 + 2" actual
     ++	git log -L:func2:file.c -G "F2 [+] 2" --format=%s --no-patch >actual &&
     ++	echo "Modify func2() in file.c" >expect &&
     ++	test_cmp expect actual
       '
     + 
     + test_expect_success 'setup for trailing deletion test' '
      @@ t/t4211-line-log.sh: test_expect_success '--check does not report blank-at-eof outside the range' '
     - 	test_grep ! "blank line at EOF" actual
     + 	test_cmp expect actual
       '
       
     -+test_expect_success '-L -G is scoped to the tracked range' '
     -+	git checkout --orphan grep-scope &&
     ++test_expect_success '-L -G is limited to the tracked range' '
     ++	git checkout --orphan grep-range &&
      +	git reset --hard &&
      +	cat >gp.c <<-\EOF &&
      +	int func1()
     @@ t/t4211-line-log.sh: test_expect_success '--check does not report blank-at-eof o
      +	sed -e "s/ALPHA/ALPHA2/" -e "s/BETA/BETA2/" gp.c >tmp &&
      +	mv tmp gp.c &&
      +	git commit -a -m "touch both functions" &&
     -+	# The commit changes ALPHA (func1) and BETA (func2).  Tracking func2,
     -+	# -G BETA matches its in-range change; -G ALPHA must not, since ALPHA
     -+	# changes only outside the tracked range.
     -+	git log -L:func2:gp.c -G BETA --format=%s >actual &&
     -+	test_grep "touch both functions" actual &&
     -+	git log -L:func2:gp.c -G ALPHA --format=%s >actual &&
     -+	test_grep ! "touch both functions" actual
     ++	git log -L:func2:gp.c -G BETA --format=%s --no-patch >actual &&
     ++	cat >expect <<-\EOF &&
     ++	touch both functions
     ++	add gp.c
     ++	EOF
     ++	test_cmp expect actual &&
     ++	git log -L:func2:gp.c -G ALPHA --format=%s --no-patch >actual &&
     ++	test_must_be_empty actual
      +'
      +
      +test_expect_success '-L -G searches the whole file under textconv' '
     @@ t/t4211-line-log.sh: test_expect_success '--check does not report blank-at-eof o
      +	git add tc.c &&
      +	test_tick &&
      +	git commit -m "add tc.c" &&
     -+	# One commit changes func1 and func2; MAGIC lands only in the
     -+	# func2 change, outside func1.
     -+	sed -e "s/F1/F1 + 1/" -e "s/return F2/return MAGIC/" tc.c >tmp &&
     ++	sed -e "s/F1/F1 + 1/" -e "s/return F2/return FINDME/" tc.c >tmp &&
      +	mv tmp tc.c &&
      +	git commit -a -m "change both funcs" &&
      +	echo "tc.c diff=tc" >.gitattributes &&
     -+
     -+	# Without a textconv driver, -G is scoped to func1, so MAGIC (only
     -+	# in the func2 change) does not select the commit.
     -+	git log -L:func1:tc.c -G MAGIC --format=%s --no-patch >actual &&
     ++	git log -L:func1:tc.c -G FINDME --format=%s --no-patch >actual &&
      +	test_must_be_empty actual &&
     -+
     -+	# A textconv driver makes the range (original-file line numbers)
     -+	# meaningless against the driver output, so -G falls back to the
     -+	# whole file and MAGIC now selects the commit.
      +	git config diff.tc.textconv cat &&
     -+	git log -L:func1:tc.c -G MAGIC --format=%s --no-patch >actual &&
     -+	test_grep "change both funcs" actual
     ++	git log -L:func1:tc.c -G FINDME --format=%s --no-patch >actual &&
     ++	echo "change both funcs" >expect &&
     ++	test_cmp expect actual
      +'
      +
       test_done
     @@ xdiff-interface.h: int xdi_diff_outf(mmfile_t *mf1, mmfile_t *mf2,
      +struct range_set;
      +/*
      + * Like xdi_diff_outf(), but forwards only the lines within the given
     -+ * (post-image) line ranges to line_fn, as "git log -L" scopes its output.
     -+ * Returns line_fn's latched return value (so a consumer can signal a hit
     -+ * with a non-zero return), or non-zero on xdiff failure.  Defined in
     -+ * diff.c (it reuses the line-range filter there).
     ++ * postimage line ranges to line_fn.
      + */
      +int diff_emit_line_ranges(mmfile_t *mf1, mmfile_t *mf2,
      +			  const struct range_set *ranges,

-- 
gitgitgadget

[PATCH v3 1/7] diff: rename line-range filter struct and clarify fields

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

diff's line-range filtering logic uses the line_range_callback
struct to represent filtering state. However, this name does not
clearly reflect the role it plays. This is especially relevant as
we expand diff's line-range filtering to work with more options,
including --stat and -G.

Also, line_range_callback's fields are terse, while the comment
explaining line_range_callback is verbose and out of place compared to
its surroundings.

Rename line_range_callback to line_range_filter, and replace the verbose
comment with a concise one, instead preferring descriptive field and
variable names that are self-explanatory over comments.

No logical behavior change. Some fields are grouped under a new struct
in the newly renamed line_range_filter. Everything else is just a
rename.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c | 270 ++++++++++++++++++++++++---------------------------------
 1 file changed, 114 insertions(+), 156 deletions(-)

diff --git a/diff.c b/diff.c
index 414532d09f..679a0e27d4 100644
--- a/diff.c
+++ b/diff.c
@@ -610,49 +610,31 @@ struct emit_callback {
 };
 
 /*
- * State for the line-range callback wrappers that sit between
- * xdi_diff_outf() and fn_out_consume().  xdiff produces a normal,
- * unfiltered diff; the wrappers intercept each hunk header and line,
- * track post-image position, and forward only lines that fall within
- * the requested ranges.  Contiguous in-range lines are collected into
- * range hunks and flushed with a synthetic @@ header so that
- * fn_out_consume() sees well-formed unified-diff fragments.
- *
- * Removal lines ('-') cannot be classified by post-image position, so
- * they are buffered in pending_rm until the next '+' or ' ' line
- * reveals whether they precede an in-range line (flush into range hunk) or
- * an out-of-range line (discard).
+ * Filter the line ranges that are emitted by diff.
  */
-struct line_range_callback {
+struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
 	void *orig_cb_data;
-	const struct range_set *ranges;	/* 0-based [start, end) */
-	unsigned int cur_range;		/* index into the range_set */
-
-	/* Post/pre-image line counters (1-based, set from hunk headers) */
-	long lno_post;
-	long lno_pre;
+	const struct range_set *range_sets_to_filter_by;
+	unsigned int range_set_idx;
+
+	struct {
+		char func_name[80];
+		long func_name_len;
+		long old_begin, old_count;
+		long new_begin, new_count;
+		long lno_in_preimage;
+		long lno_in_postimage;
+		struct strbuf lines;
+		int active;
+		int has_changes;
+	} accumulating_hunk;
 
-	/*
-	 * Function name from most recent xdiff hunk header;
-	 * size matches struct func_line.buf in xdiff/xemit.c.
-	 */
-	char func[80];
-	long funclen;
-
-	/* Range hunk being accumulated for the current range */
-	struct strbuf rhunk;
-	long rhunk_old_begin, rhunk_old_count;
-	long rhunk_new_begin, rhunk_new_count;
-	int rhunk_active;
-	int rhunk_has_changes;		/* any '+' or '-' lines? */
-
-	/* Removal lines not yet known to be in-range */
 	struct strbuf pending_rm;
 	int pending_rm_count;
-	long pending_rm_pre_begin;	/* pre-image line of first pending */
+	long pending_rm_pre_begin;
 
-	int ret;			/* latched error from orig_line_fn */
+	int ret;
 };
 
 static int count_lines(const char *data, int size)
@@ -2540,69 +2522,59 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
-static void discard_pending_rm(struct line_range_callback *s)
+static void discard_pending_rm(struct line_range_filter *filter)
 {
-	strbuf_reset(&s->pending_rm);
-	s->pending_rm_count = 0;
+	strbuf_reset(&filter->pending_rm);
+	filter->pending_rm_count = 0;
 }
 
-static void flush_rhunk(struct line_range_callback *s)
+static void flush_range_hunk(struct line_range_filter *filter)
 {
 	struct strbuf hdr = STRBUF_INIT;
-	const char *p, *end;
+	const char *line_buf, *line_buf_end;
 
-	if (!s->rhunk_active || s->ret)
+	if (!filter->accumulating_hunk.active || filter->ret)
 		return;
 
-	/* Drain any pending removal lines into the range hunk */
-	if (s->pending_rm_count) {
-		strbuf_addbuf(&s->rhunk, &s->pending_rm);
-		s->rhunk_old_count += s->pending_rm_count;
-		s->rhunk_has_changes = 1;
-		discard_pending_rm(s);
+	if (filter->pending_rm_count) {
+		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
+		filter->accumulating_hunk.old_count += filter->pending_rm_count;
+		filter->accumulating_hunk.has_changes = 1;
+		discard_pending_rm(filter);
 	}
 
-	/*
-	 * Suppress context-only hunks: they contain no actual changes
-	 * and would just be noise.  This can happen when the inflated
-	 * ctxlen causes xdiff to emit context covering a range that
-	 * has no changes in this commit.
-	 */
-	if (!s->rhunk_has_changes) {
-		s->rhunk_active = 0;
-		strbuf_reset(&s->rhunk);
+	if (!filter->accumulating_hunk.has_changes) {
+		filter->accumulating_hunk.active = 0;
+		strbuf_reset(&filter->accumulating_hunk.lines);
 		return;
 	}
 
 	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    s->rhunk_old_begin, s->rhunk_old_count,
-		    s->rhunk_new_begin, s->rhunk_new_count);
-	if (s->funclen > 0) {
+		    filter->accumulating_hunk.old_begin, filter->accumulating_hunk.old_count,
+		    filter->accumulating_hunk.new_begin, filter->accumulating_hunk.new_count);
+	if (filter->accumulating_hunk.func_name_len > 0) {
 		strbuf_addch(&hdr, ' ');
-		strbuf_add(&hdr, s->func, s->funclen);
+		strbuf_add(&hdr, filter->accumulating_hunk.func_name,
+	     filter->accumulating_hunk.func_name_len);
 	}
 	strbuf_addch(&hdr, '\n');
 
-	s->ret = s->orig_line_fn(s->orig_cb_data, hdr.buf, hdr.len);
+	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
 
-	/*
-	 * Replay buffered lines one at a time through fn_out_consume.
-	 * The cast discards const because xdiff_emit_line_fn takes
-	 * char *, though fn_out_consume does not modify the buffer.
-	 */
-	p = s->rhunk.buf;
-	end = p + s->rhunk.len;
-	while (!s->ret && p < end) {
-		const char *eol = memchr(p, '\n', end - p);
-		unsigned long line_len = eol ? (unsigned long)(eol - p + 1)
-					     : (unsigned long)(end - p);
-		s->ret = s->orig_line_fn(s->orig_cb_data, (char *)p, line_len);
-		p += line_len;
+	line_buf = filter->accumulating_hunk.lines.buf;
+	line_buf_end = line_buf + filter->accumulating_hunk.lines.len;
+	while (!filter->ret && line_buf < line_buf_end) {
+		const char *eol = memchr(line_buf, '\n', line_buf_end - line_buf);
+		unsigned long line_len = eol ? (unsigned long)(eol - line_buf + 1)
+					     : (unsigned long)(line_buf_end - line_buf);
+		filter->ret = filter->orig_line_fn(filter->orig_cb_data,
+				     (char *)line_buf, line_len);
+		line_buf += line_len;
 	}
 
-	s->rhunk_active = 0;
-	strbuf_reset(&s->rhunk);
+	filter->accumulating_hunk.active = 0;
+	strbuf_reset(&filter->accumulating_hunk.lines);
 }
 
 static void line_range_hunk_fn(void *data,
@@ -2610,116 +2582,102 @@ static void line_range_hunk_fn(void *data,
 			       long new_begin, long new_nr UNUSED,
 			       const char *func, long funclen)
 {
-	struct line_range_callback *s = data;
+	struct line_range_filter *filter = data;
 
-	/*
-	 * When count > 0, begin is 1-based.  When count == 0, begin is
-	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
-	 * that type will arrive, so the value is unused.
-	 *
-	 * Any pending removal lines from the previous xdiff hunk are
-	 * intentionally left in pending_rm: the line callback will
-	 * flush or discard them when the next content line reveals
-	 * whether the removals precede in-range content.
-	 */
-	s->lno_post = new_begin;
-	s->lno_pre = old_begin;
+	filter->accumulating_hunk.lno_in_postimage = new_begin;
+	filter->accumulating_hunk.lno_in_preimage = old_begin;
 
 	if (funclen > 0) {
-		if (funclen > (long)sizeof(s->func))
-			funclen = sizeof(s->func);
-		memcpy(s->func, func, funclen);
+		if (funclen > (long)sizeof(filter->accumulating_hunk.func_name))
+			funclen = sizeof(filter->accumulating_hunk.func_name);
+		memcpy(filter->accumulating_hunk.func_name, func, funclen);
 	}
-	s->funclen = funclen;
+	filter->accumulating_hunk.func_name_len = funclen;
 }
 
 static int line_range_line_fn(void *priv, char *line, unsigned long len)
 {
-	struct line_range_callback *s = priv;
+	struct line_range_filter *filter = priv;
 	const struct range *cur;
-	long lno_0, cur_pre;
+	long idx_in_postimage, cur_pre;
 
-	if (s->ret)
-		return s->ret;
+	if (filter->ret)
+		return filter->ret;
 
 	if (line[0] == '-') {
-		if (!s->pending_rm_count)
-			s->pending_rm_pre_begin = s->lno_pre;
-		s->lno_pre++;
-		strbuf_add(&s->pending_rm, line, len);
-		s->pending_rm_count++;
-		return s->ret;
+		if (!filter->pending_rm_count)
+			filter->pending_rm_pre_begin =
+				filter->accumulating_hunk.lno_in_preimage;
+		filter->accumulating_hunk.lno_in_preimage++;
+		strbuf_add(&filter->pending_rm, line, len);
+		filter->pending_rm_count++;
+		return filter->ret;
 	}
 
 	if (line[0] == '\\') {
-		if (s->pending_rm_count)
-			strbuf_add(&s->pending_rm, line, len);
-		else if (s->rhunk_active)
-			strbuf_add(&s->rhunk, line, len);
-		/* otherwise outside tracked range; drop silently */
-		return s->ret;
+		if (filter->pending_rm_count)
+			strbuf_add(&filter->pending_rm, line, len);
+		else if (filter->accumulating_hunk.active)
+			strbuf_add(&filter->accumulating_hunk.lines, line, len);
+		return filter->ret;
 	}
 
 	if (line[0] != '+' && line[0] != ' ')
 		BUG("unexpected diff line type '%c'", line[0]);
 
-	lno_0 = s->lno_post - 1;
-	cur_pre = s->lno_pre;	/* save before advancing for context lines */
-	s->lno_post++;
+	idx_in_postimage = filter->accumulating_hunk.lno_in_postimage - 1;
+	cur_pre = filter->accumulating_hunk.lno_in_preimage;
+	filter->accumulating_hunk.lno_in_postimage++;
 	if (line[0] == ' ')
-		s->lno_pre++;
+		filter->accumulating_hunk.lno_in_preimage++;
 
-	/* Advance past ranges we've passed */
-	while (s->cur_range < s->ranges->nr &&
-	       lno_0 >= s->ranges->ranges[s->cur_range].end) {
-		if (s->rhunk_active)
-			flush_rhunk(s);
-		discard_pending_rm(s);
-		s->cur_range++;
+	while (filter->range_set_idx < filter->range_sets_to_filter_by->nr &&
+	       idx_in_postimage >=
+		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].end) {
+		if (filter->accumulating_hunk.active)
+			flush_range_hunk(filter);
+		discard_pending_rm(filter);
+		filter->range_set_idx++;
 	}
 
-	/* Past all ranges */
-	if (s->cur_range >= s->ranges->nr) {
-		discard_pending_rm(s);
-		return s->ret;
+	if (filter->range_set_idx >= filter->range_sets_to_filter_by->nr) {
+		discard_pending_rm(filter);
+		return filter->ret;
 	}
 
-	cur = &s->ranges->ranges[s->cur_range];
+	cur = &filter->range_sets_to_filter_by->ranges[filter->range_set_idx];
 
-	/* Before current range */
-	if (lno_0 < cur->start) {
-		discard_pending_rm(s);
-		return s->ret;
+	if (idx_in_postimage < cur->start) {
+		discard_pending_rm(filter);
+		return filter->ret;
 	}
 
-	/* In range so start a new range hunk if needed */
-	if (!s->rhunk_active) {
-		s->rhunk_active = 1;
-		s->rhunk_has_changes = 0;
-		s->rhunk_new_begin = lno_0 + 1;
-		s->rhunk_old_begin = s->pending_rm_count
-			? s->pending_rm_pre_begin : cur_pre;
-		s->rhunk_old_count = 0;
-		s->rhunk_new_count = 0;
-		strbuf_reset(&s->rhunk);
+	if (!filter->accumulating_hunk.active) {
+		filter->accumulating_hunk.active = 1;
+		filter->accumulating_hunk.has_changes = 0;
+		filter->accumulating_hunk.new_begin = idx_in_postimage + 1;
+		filter->accumulating_hunk.old_begin = filter->pending_rm_count
+			? filter->pending_rm_pre_begin : cur_pre;
+		filter->accumulating_hunk.old_count = 0;
+		filter->accumulating_hunk.new_count = 0;
+		strbuf_reset(&filter->accumulating_hunk.lines);
 	}
 
-	/* Flush pending removals into range hunk */
-	if (s->pending_rm_count) {
-		strbuf_addbuf(&s->rhunk, &s->pending_rm);
-		s->rhunk_old_count += s->pending_rm_count;
-		s->rhunk_has_changes = 1;
-		discard_pending_rm(s);
+	if (filter->pending_rm_count) {
+		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
+		filter->accumulating_hunk.old_count += filter->pending_rm_count;
+		filter->accumulating_hunk.has_changes = 1;
+		discard_pending_rm(filter);
 	}
 
-	strbuf_add(&s->rhunk, line, len);
-	s->rhunk_new_count++;
+	strbuf_add(&filter->accumulating_hunk.lines, line, len);
+	filter->accumulating_hunk.new_count++;
 	if (line[0] == '+')
-		s->rhunk_has_changes = 1;
+		filter->accumulating_hunk.has_changes = 1;
 	else
-		s->rhunk_old_count++;
+		filter->accumulating_hunk.old_count++;
 
-	return s->ret;
+	return filter->ret;
 }
 
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
@@ -4066,15 +4024,15 @@ static void builtin_diff(const char *name_a,
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
 		} else if (line_ranges) {
-			struct line_range_callback lr_state;
+			struct line_range_filter lr_state;
 			unsigned int i;
 			long max_span = 0;
 
 			memset(&lr_state, 0, sizeof(lr_state));
 			lr_state.orig_line_fn = fn_out_consume;
 			lr_state.orig_cb_data = &ecbdata;
-			lr_state.ranges = line_ranges;
-			strbuf_init(&lr_state.rhunk, 0);
+			lr_state.range_sets_to_filter_by = line_ranges;
+			strbuf_init(&lr_state.accumulating_hunk.lines, 0);
 			strbuf_init(&lr_state.pending_rm, 0);
 
 			/*
@@ -4105,11 +4063,11 @@ static void builtin_diff(const char *name_a,
 				die("unable to generate diff for %s",
 				    one->path);
 
-			flush_rhunk(&lr_state);
+			flush_range_hunk(&lr_state);
 			if (lr_state.ret)
 				die("unable to generate diff for %s",
 				    one->path);
-			strbuf_release(&lr_state.rhunk);
+			strbuf_release(&lr_state.accumulating_hunk.lines);
 			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
-- 
gitgitgadget

[PATCH v3 2/7] diff: simplify the line-range filter by classifying removals immediately

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Currently, the diff line-range filter buffers preimage removal lines
until a postimage line arrives. That line's number confirms whether the
preimage line falls in a relevant range. However, storing preimage
lines in a separate buffer is unnecessary. Worse, the logic has a bug:
a preimage line outside the target range is included when it
immediately follows an in-range postimage line.

Preimage lines will always precede their postimage counterpart both in
content line number and emission order from xdiff's line callback
function. So preimage lines can share the postimage buffer. The filter
flushes them based on whether the postimage lines fall within the
target range.

Remove logic related to storing preimage lines in a separate "removal"
buffer and prepending them to the accumulating_hunk's line buffer.
Instead, store those lines in the accumulating_hunk's line_buffer
immediately and flush everything as appropriate based on postimage
line numbers that arrive. This resolves the bug by construction.

Also, calculate the old and new line counts for the diff hunk header
when flushing rather than storing counters in line_range_filter to
simplify state management further.

Add a test to t/t4211-line-log.sh that verifies the preimage line
emission bug is fixed.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c              | 121 +++++++++++++++++---------------------------
 t/t4211-line-log.sh |  31 ++++++++++++
 2 files changed, 78 insertions(+), 74 deletions(-)

diff --git a/diff.c b/diff.c
index 679a0e27d4..c94ddbebe5 100644
--- a/diff.c
+++ b/diff.c
@@ -621,19 +621,14 @@ struct line_range_filter {
 	struct {
 		char func_name[80];
 		long func_name_len;
-		long old_begin, old_count;
-		long new_begin, new_count;
+		long old_begin;
+		long new_begin;
 		long lno_in_preimage;
 		long lno_in_postimage;
 		struct strbuf lines;
 		int active;
-		int has_changes;
 	} accumulating_hunk;
 
-	struct strbuf pending_rm;
-	int pending_rm_count;
-	long pending_rm_pre_begin;
-
 	int ret;
 };
 
@@ -2522,40 +2517,56 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
-static void discard_pending_rm(struct line_range_filter *filter)
+static void begin_range_hunk(struct line_range_filter *filter)
 {
-	strbuf_reset(&filter->pending_rm);
-	filter->pending_rm_count = 0;
+	filter->accumulating_hunk.active = 1;
+	filter->accumulating_hunk.new_begin = filter->accumulating_hunk.lno_in_postimage;
+	filter->accumulating_hunk.old_begin = filter->accumulating_hunk.lno_in_preimage;
+	strbuf_reset(&filter->accumulating_hunk.lines);
 }
 
 static void flush_range_hunk(struct line_range_filter *filter)
 {
 	struct strbuf hdr = STRBUF_INIT;
 	const char *line_buf, *line_buf_end;
+	long old_count = 0, new_count = 0;
+	int has_changes = 0;
 
 	if (!filter->accumulating_hunk.active || filter->ret)
 		return;
 
-	if (filter->pending_rm_count) {
-		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
-		filter->accumulating_hunk.old_count += filter->pending_rm_count;
-		filter->accumulating_hunk.has_changes = 1;
-		discard_pending_rm(filter);
+	line_buf = filter->accumulating_hunk.lines.buf;
+	line_buf_end = line_buf + filter->accumulating_hunk.lines.len;
+	while (line_buf < line_buf_end) {
+		const char *eol = memchr(line_buf, '\n', line_buf_end - line_buf);
+		if (*line_buf == ' ') {
+			old_count++;
+			new_count++;
+		}
+		else if (*line_buf == '-') {
+			old_count++;
+			has_changes = 1;
+		}
+		else if (*line_buf == '+') {
+			new_count++;
+			has_changes = 1;
+		}
+		line_buf = eol ? eol + 1 : line_buf_end;
 	}
 
-	if (!filter->accumulating_hunk.has_changes) {
+	if (!has_changes) {
 		filter->accumulating_hunk.active = 0;
 		strbuf_reset(&filter->accumulating_hunk.lines);
 		return;
 	}
 
 	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    filter->accumulating_hunk.old_begin, filter->accumulating_hunk.old_count,
-		    filter->accumulating_hunk.new_begin, filter->accumulating_hunk.new_count);
+		    filter->accumulating_hunk.old_begin, old_count,
+		    filter->accumulating_hunk.new_begin, new_count);
 	if (filter->accumulating_hunk.func_name_len > 0) {
 		strbuf_addch(&hdr, ' ');
 		strbuf_add(&hdr, filter->accumulating_hunk.func_name,
-	     filter->accumulating_hunk.func_name_len);
+			   filter->accumulating_hunk.func_name_len);
 	}
 	strbuf_addch(&hdr, '\n');
 
@@ -2598,84 +2609,48 @@ static void line_range_hunk_fn(void *data,
 static int line_range_line_fn(void *priv, char *line, unsigned long len)
 {
 	struct line_range_filter *filter = priv;
-	const struct range *cur;
-	long idx_in_postimage, cur_pre;
+	long idx_in_postimage;
+	int in_range;
 
 	if (filter->ret)
 		return filter->ret;
 
-	if (line[0] == '-') {
-		if (!filter->pending_rm_count)
-			filter->pending_rm_pre_begin =
-				filter->accumulating_hunk.lno_in_preimage;
-		filter->accumulating_hunk.lno_in_preimage++;
-		strbuf_add(&filter->pending_rm, line, len);
-		filter->pending_rm_count++;
-		return filter->ret;
-	}
-
 	if (line[0] == '\\') {
-		if (filter->pending_rm_count)
-			strbuf_add(&filter->pending_rm, line, len);
-		else if (filter->accumulating_hunk.active)
+		if (filter->accumulating_hunk.active)
 			strbuf_add(&filter->accumulating_hunk.lines, line, len);
 		return filter->ret;
 	}
 
-	if (line[0] != '+' && line[0] != ' ')
+	if (line[0] != '+' && line[0] != ' ' && line[0] != '-')
 		BUG("unexpected diff line type '%c'", line[0]);
 
 	idx_in_postimage = filter->accumulating_hunk.lno_in_postimage - 1;
-	cur_pre = filter->accumulating_hunk.lno_in_preimage;
-	filter->accumulating_hunk.lno_in_postimage++;
-	if (line[0] == ' ')
-		filter->accumulating_hunk.lno_in_preimage++;
 
 	while (filter->range_set_idx < filter->range_sets_to_filter_by->nr &&
 	       idx_in_postimage >=
 		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].end) {
 		if (filter->accumulating_hunk.active)
 			flush_range_hunk(filter);
-		discard_pending_rm(filter);
 		filter->range_set_idx++;
 	}
 
-	if (filter->range_set_idx >= filter->range_sets_to_filter_by->nr) {
-		discard_pending_rm(filter);
-		return filter->ret;
-	}
-
-	cur = &filter->range_sets_to_filter_by->ranges[filter->range_set_idx];
-
-	if (idx_in_postimage < cur->start) {
-		discard_pending_rm(filter);
-		return filter->ret;
-	}
+	in_range = filter->range_set_idx < filter->range_sets_to_filter_by->nr &&
+		   idx_in_postimage >=
+		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].start &&
+		   idx_in_postimage <
+		filter->range_sets_to_filter_by->ranges[filter->range_set_idx].end;
 
-	if (!filter->accumulating_hunk.active) {
-		filter->accumulating_hunk.active = 1;
-		filter->accumulating_hunk.has_changes = 0;
-		filter->accumulating_hunk.new_begin = idx_in_postimage + 1;
-		filter->accumulating_hunk.old_begin = filter->pending_rm_count
-			? filter->pending_rm_pre_begin : cur_pre;
-		filter->accumulating_hunk.old_count = 0;
-		filter->accumulating_hunk.new_count = 0;
-		strbuf_reset(&filter->accumulating_hunk.lines);
-	}
+	if (in_range) {
+		if (!filter->accumulating_hunk.active)
+			begin_range_hunk(filter);
 
-	if (filter->pending_rm_count) {
-		strbuf_addbuf(&filter->accumulating_hunk.lines, &filter->pending_rm);
-		filter->accumulating_hunk.old_count += filter->pending_rm_count;
-		filter->accumulating_hunk.has_changes = 1;
-		discard_pending_rm(filter);
+		strbuf_add(&filter->accumulating_hunk.lines, line, len);
 	}
 
-	strbuf_add(&filter->accumulating_hunk.lines, line, len);
-	filter->accumulating_hunk.new_count++;
-	if (line[0] == '+')
-		filter->accumulating_hunk.has_changes = 1;
-	else
-		filter->accumulating_hunk.old_count++;
+	if (line[0] == ' ' || line[0] == '+')
+		filter->accumulating_hunk.lno_in_postimage++;
+	if (line[0] == ' ' || line[0] == '-')
+		filter->accumulating_hunk.lno_in_preimage++;
 
 	return filter->ret;
 }
@@ -4033,7 +4008,6 @@ static void builtin_diff(const char *name_a,
 			lr_state.orig_cb_data = &ecbdata;
 			lr_state.range_sets_to_filter_by = line_ranges;
 			strbuf_init(&lr_state.accumulating_hunk.lines, 0);
-			strbuf_init(&lr_state.pending_rm, 0);
 
 			/*
 			 * Inflate ctxlen so that all changes within
@@ -4068,7 +4042,6 @@ static void builtin_diff(const char *name_a,
 				die("unable to generate diff for %s",
 				    one->path);
 			strbuf_release(&lr_state.accumulating_hunk.lines);
-			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index d0a834ed8f..233dc232e3 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -738,6 +738,37 @@ test_expect_success '-L with -G filters to diff-text matches' '
 	test_grep "F2 + 2" actual
 '
 
+test_expect_success 'setup for trailing deletion test' '
+	git checkout --orphan trailing-del &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 1;
+	}
+	// trailing comment outside tracked range
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "add file with trailing comment" &&
+	# Remove the trailing comment AND modify tracked() so there
+	# is a modification to the line range we track and a
+	# modification to the following line, which we do not track.
+	cat >file.c <<-\EOF &&
+	void tracked()
+	{
+	    return 2;
+	}
+	EOF
+	git commit -a -m "modify tracked and delete trailing comment"
+'
+
+test_expect_success '-L does not include deletions past end of tracked range' '
+	git log -L:tracked:file.c --format= -1 -p >actual &&
+	test_grep "return 2" actual &&
+	test_grep ! "trailing comment" actual
+'
+
 test_expect_success '-L with --diff-filter=M excludes root commit' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c --diff-filter=M --format=%s --no-patch >actual &&
-- 
gitgitgadget

[PATCH v3 3/7] diff: emit -L hunk headers via xdiff's formatter

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Currently, diff's line-range filter implements its own method for
emitting diff hunk headers. This mostly matches what xdiff itself
outputs, but there is a discrepancy for postimage or preimage sides
with 0 line changes. For a side with no lines (count 0), the begin is
the line before the change. The header omits the line count of 1.

Rather than fix this case in the line-range implementation, expose the
function xdiff uses to emit its headers. Reusing it keeps the header
format consistent with and without -L.

Update test scenarios and fixtures to reflect the now consistent header
format.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c                                   | 21 ++++++++-------------
 t/t4211/sha1/expect.no-assertion-error   |  2 +-
 t/t4211/sha1/expect.vanishes-early       |  6 +++---
 t/t4211/sha256/expect.no-assertion-error |  2 +-
 t/t4211/sha256/expect.vanishes-early     |  6 +++---
 xdiff-interface.c                        | 19 +++++++++++++++++++
 xdiff-interface.h                        | 13 +++++++++++++
 7 files changed, 48 insertions(+), 21 deletions(-)

diff --git a/diff.c b/diff.c
index c94ddbebe5..cb1a85c624 100644
--- a/diff.c
+++ b/diff.c
@@ -2560,15 +2560,10 @@ static void flush_range_hunk(struct line_range_filter *filter)
 		return;
 	}
 
-	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
-		    filter->accumulating_hunk.old_begin, old_count,
-		    filter->accumulating_hunk.new_begin, new_count);
-	if (filter->accumulating_hunk.func_name_len > 0) {
-		strbuf_addch(&hdr, ' ');
-		strbuf_add(&hdr, filter->accumulating_hunk.func_name,
-			   filter->accumulating_hunk.func_name_len);
-	}
-	strbuf_addch(&hdr, '\n');
+	xdiff_emit_hunk_header(&hdr, filter->accumulating_hunk.old_begin, old_count,
+			       filter->accumulating_hunk.new_begin, new_count,
+			       filter->accumulating_hunk.func_name,
+			filter->accumulating_hunk.func_name_len);
 
 	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
@@ -2589,14 +2584,14 @@ static void flush_range_hunk(struct line_range_filter *filter)
 }
 
 static void line_range_hunk_fn(void *data,
-			       long old_begin, long old_nr UNUSED,
-			       long new_begin, long new_nr UNUSED,
+			       long old_begin, long old_nr,
+			       long new_begin, long new_nr,
 			       const char *func, long funclen)
 {
 	struct line_range_filter *filter = data;
 
-	filter->accumulating_hunk.lno_in_postimage = new_begin;
-	filter->accumulating_hunk.lno_in_preimage = old_begin;
+	filter->accumulating_hunk.lno_in_postimage = new_nr ? new_begin : new_begin + 1;
+	filter->accumulating_hunk.lno_in_preimage = old_nr ? old_begin : old_begin + 1;
 
 	if (funclen > 0) {
 		if (funclen > (long)sizeof(filter->accumulating_hunk.func_name))
diff --git a/t/t4211/sha1/expect.no-assertion-error b/t/t4211/sha1/expect.no-assertion-error
index 54c568f273..95faf51a7b 100644
--- a/t/t4211/sha1/expect.no-assertion-error
+++ b/t/t4211/sha1/expect.no-assertion-error
@@ -8,7 +8,7 @@ diff --git a/b.c b/b.c
 index bf79c2f..27c829c 100644
 --- a/b.c
 +++ b/b.c
-@@ -25,0 +18,9 @@
+@@ -24,0 +18,9 @@
 +long f(long x)
 +{
 +	int s = 0;
diff --git a/t/t4211/sha1/expect.vanishes-early b/t/t4211/sha1/expect.vanishes-early
index a413ad3659..e4b1a201d5 100644
--- a/t/t4211/sha1/expect.vanishes-early
+++ b/t/t4211/sha1/expect.vanishes-early
@@ -8,7 +8,7 @@ diff --git a/a.c b/a.c
 index 0b9cae5..5de3ea4 100644
 --- a/a.c
 +++ b/a.c
-@@ -23,0 +24,1 @@ int main ()
+@@ -22,0 +24 @@ int main ()
 +/* incomplete lines are bad! */
 
 commit 100b61a6f2f720f812620a9d10afb3a960ccb73c
@@ -21,7 +21,7 @@ diff --git a/a.c b/a.c
 index 5e709a1..0b9cae5 100644
 --- a/a.c
 +++ b/a.c
-@@ -22,1 +22,1 @@ int main ()
+@@ -22 +22 @@ int main ()
 -}
 +}
 \ No newline at end of file
@@ -37,5 +37,5 @@ new file mode 100644
 index 0000000..444e415
 --- /dev/null
 +++ b/a.c
-@@ -0,0 +20,1 @@
+@@ -0,0 +20 @@
 +}
diff --git a/t/t4211/sha256/expect.no-assertion-error b/t/t4211/sha256/expect.no-assertion-error
index c25f2ce19c..815d27f7f1 100644
--- a/t/t4211/sha256/expect.no-assertion-error
+++ b/t/t4211/sha256/expect.no-assertion-error
@@ -8,7 +8,7 @@ diff --git a/b.c b/b.c
 index 69cb69c..a0d566e 100644
 --- a/b.c
 +++ b/b.c
-@@ -25,0 +18,9 @@
+@@ -24,0 +18,9 @@
 +long f(long x)
 +{
 +	int s = 0;
diff --git a/t/t4211/sha256/expect.vanishes-early b/t/t4211/sha256/expect.vanishes-early
index bc33b963dc..263fc9eaac 100644
--- a/t/t4211/sha256/expect.vanishes-early
+++ b/t/t4211/sha256/expect.vanishes-early
@@ -8,7 +8,7 @@ diff --git a/a.c b/a.c
 index e4fa1d8..62c1fc2 100644
 --- a/a.c
 +++ b/a.c
-@@ -23,0 +24,1 @@ int main ()
+@@ -22,0 +24 @@ int main ()
 +/* incomplete lines are bad! */
 
 commit 29f32ac3141c48b22803e5c4127b719917b67d0f8ca8c5248bebfa2a19f7da10
@@ -21,7 +21,7 @@ diff --git a/a.c b/a.c
 index d325124..e4fa1d8 100644
 --- a/a.c
 +++ b/a.c
-@@ -22,1 +22,1 @@ int main ()
+@@ -22 +22 @@ int main ()
 -}
 +}
 \ No newline at end of file
@@ -37,5 +37,5 @@ new file mode 100644
 index 0000000..9f550c3
 --- /dev/null
 +++ b/a.c
-@@ -0,0 +20,1 @@
+@@ -0,0 +20 @@
 +}
diff --git a/xdiff-interface.c b/xdiff-interface.c
index db6938689f..686db8bb8b 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -91,6 +91,25 @@ static int xdiff_outf(void *priv_, mmbuffer_t *mb, int nbuf)
 	return 0;
 }
 
+static int strbuf_out_line(void *priv, mmbuffer_t *mb, int nbuf)
+{
+	struct strbuf *out = priv;
+	int i;
+	for (i = 0; i < nbuf; i++)
+		strbuf_add(out, mb[i].ptr, mb[i].size);
+	return 0;
+}
+
+void xdiff_emit_hunk_header(struct strbuf *out,
+			    long old_begin, long old_count,
+			    long new_begin, long new_count,
+			    const char *func, long funclen)
+{
+	xdemitcb_t ecb = { .priv = out, .out_line = strbuf_out_line };
+	xdl_emit_hunk_hdr(old_begin, old_count, new_begin, new_count,
+			  func, funclen, &ecb);
+}
+
 /*
  * Trim down common substring at the end of the buffers,
  * but end on a complete line.
diff --git a/xdiff-interface.h b/xdiff-interface.h
index ce54e1c0e0..2428456629 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -76,4 +76,17 @@ int xdiff_compare_lines(const char *l1, long s1,
  */
 unsigned long xdiff_hash_string(const char *s, size_t len, long flags);
 
+struct strbuf;
+
+/*
+ * Append a unified-diff hunk header to `out`, e.g.
+ * "@@ -<old> +<new> @@ func\n". The header comes from wrapping xdiff's
+ * own hunk-header emitter, so it matches what a normal diff would
+ * produce for the given line number begins and line counts.
+ */
+void xdiff_emit_hunk_header(struct strbuf *out,
+			    long old_begin, long old_nr,
+			    long new_begin, long new_nr,
+			    const char *func, long funclen);
+
 #endif
-- 
gitgitgadget

[PATCH v3 4/7] diff: extract a line-range diff helper for reuse

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Extract logic for initializing the line-range filter and running a diff
for a specific line range. This logic is needed for any diff that
targets a line range independent of the current patch display path.

The subsequent commits use this logic to enable additional line range
targeted diff modes.

No logical behavior change.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 diff.c | 87 ++++++++++++++++++++++++++++++++--------------------------
 1 file changed, 48 insertions(+), 39 deletions(-)

diff --git a/diff.c b/diff.c
index cb1a85c624..a7604a773a 100644
--- a/diff.c
+++ b/diff.c
@@ -2517,6 +2517,18 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
+static void line_range_filter_init(struct line_range_filter *filter,
+				   const struct range_set *ranges,
+				   xdiff_emit_line_fn line_fn,
+				   void *cb_data)
+{
+	memset(filter, 0, sizeof(*filter));
+	filter->orig_line_fn = line_fn;
+	filter->orig_cb_data = cb_data;
+	filter->range_sets_to_filter_by = ranges;
+	strbuf_init(&filter->accumulating_hunk.lines, 0);
+}
+
 static void begin_range_hunk(struct line_range_filter *filter)
 {
 	filter->accumulating_hunk.active = 1;
@@ -2650,6 +2662,37 @@ static int line_range_line_fn(void *priv, char *line, unsigned long len)
 	return filter->ret;
 }
 
+
+static int line_range_filter_diff(struct line_range_filter *filter,
+				  mmfile_t *mf1, mmfile_t *mf2,
+				  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	const struct range_set *ranges = filter->range_sets_to_filter_by;
+	long max_span = 0;
+	unsigned int i;
+	int ret;
+
+	for (i = 0; i < ranges->nr; i++) {
+		long span = ranges->ranges[i].end - ranges->ranges[i].start;
+		if (span > max_span)
+			max_span = span;
+	}
+	if (max_span > xecfg->ctxlen)
+		xecfg->ctxlen = max_span;
+
+	/* the filter seeds its per-image position from hunk headers */
+	xecfg->flags &= ~XDL_EMIT_NO_HUNK_HDR;
+
+	ret = xdi_diff_outf(mf1, mf2, line_range_hunk_fn,
+			    line_range_line_fn, filter, xpp, xecfg);
+	if (!ret) {
+		flush_range_hunk(filter);
+		ret = filter->ret;
+	}
+	strbuf_release(&filter->accumulating_hunk.lines);
+	return ret;
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
@@ -3994,49 +4037,15 @@ static void builtin_diff(const char *name_a,
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
 		} else if (line_ranges) {
-			struct line_range_filter lr_state;
-			unsigned int i;
-			long max_span = 0;
+			struct line_range_filter lr_filter;
 
-			memset(&lr_state, 0, sizeof(lr_state));
-			lr_state.orig_line_fn = fn_out_consume;
-			lr_state.orig_cb_data = &ecbdata;
-			lr_state.range_sets_to_filter_by = line_ranges;
-			strbuf_init(&lr_state.accumulating_hunk.lines, 0);
-
-			/*
-			 * Inflate ctxlen so that all changes within
-			 * any single range are merged into one xdiff
-			 * hunk and the inter-change context is emitted.
-			 * The callback clips back to range boundaries.
-			 *
-			 * The optimal ctxlen depends on where changes
-			 * fall within the range, which is only known
-			 * after xdiff runs; the max range span is the
-			 * upper bound that guarantees correctness in a
-			 * single pass.
-			 */
-			for (i = 0; i < line_ranges->nr; i++) {
-				long span = line_ranges->ranges[i].end -
-					    line_ranges->ranges[i].start;
-				if (span > max_span)
-					max_span = span;
-			}
-			if (max_span > xecfg.ctxlen)
-				xecfg.ctxlen = max_span;
-
-			if (xdi_diff_outf(&mf1, &mf2,
-					  line_range_hunk_fn,
-					  line_range_line_fn,
-					  &lr_state, &xpp, &xecfg))
-				die("unable to generate diff for %s",
-				    one->path);
+			line_range_filter_init(&lr_filter, line_ranges,
+					       fn_out_consume, &ecbdata);
 
-			flush_range_hunk(&lr_state);
-			if (lr_state.ret)
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
 				die("unable to generate diff for %s",
 				    one->path);
-			strbuf_release(&lr_state.accumulating_hunk.lines);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
-- 
gitgitgadget

[PATCH v3 5/7] diff: support stat formats with -L

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Reuse the line_range_filter in builtin_diffstat() so -L supports
the stat formats and add tests verifying the new behavior.

Ungate the newly enabled options and drop "yet" from the generic
-L rejection message ("does not yet support the requested diff
format"). Some rejected formats do not fit -L at all, so "yet"
wrongly implies they are all awaiting support.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  10 +-
 diff.c                                |  13 ++-
 revision.c                            |   6 +-
 t/t4211-line-log.sh                   | 130 ++++++++++++++++++++++----
 4 files changed, 133 insertions(+), 26 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index 72f639b5e7..b3e8b5c62c 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -9,10 +9,12 @@
 	_<start>_ and _<end>_ (or _<funcname>_) must exist in the starting revision.
 	You can specify this option more than once. Implies `--patch`.
 	Patch output can be suppressed using `--no-patch`.
-	Non-patch diff formats `--raw`, `--name-only`, `--name-status`,
-	and `--summary` are supported.  Diff stat formats
-	(`--stat`, `--numstat`, `--shortstat`, `--dirstat`) are not
-	currently implemented.
+	The following non-patch diff formats are supported: `--raw`,
+	`--name-only`, `--name-status`, `--summary`, `--stat`, `--numstat`,
+	and `--shortstat`. The stat formats count only lines within the tracked
+	range. `--dirstat` is not supported with `-L`: it summarizes change as each
+	directory's share of the total churn, not as counts for the tracked lines.
+	Use `--numstat` for exact per-file counts within the range.
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
diff --git a/diff.c b/diff.c
index a7604a773a..4a30d7b631 100644
--- a/diff.c
+++ b/diff.c
@@ -4162,7 +4162,18 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 		xecfg.ctxlen = o->context;
 		xecfg.interhunkctxlen = o->interhunkcontext;
 		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
-		if (xdi_diff_outf(&mf1, &mf2, NULL,
+
+		if (p->line_ranges) {
+			struct line_range_filter lr_filter;
+
+			line_range_filter_init(&lr_filter, p->line_ranges,
+					       diffstat_consume, diffstat);
+
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
+				die("unable to generate diffstat for %s",
+				    one->path);
+		} else if (xdi_diff_outf(&mf1, &mf2, NULL,
 				  diffstat_consume, diffstat, &xpp, &xecfg))
 			die("unable to generate diffstat for %s", one->path);
 
diff --git a/revision.c b/revision.c
index 35afe52208..4639c0df8e 100644
--- a/revision.c
+++ b/revision.c
@@ -3229,8 +3229,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 	     (revs->diffopt.output_format &
 	      ~(DIFF_FORMAT_PATCH | DIFF_FORMAT_NO_OUTPUT |
 		DIFF_FORMAT_RAW | DIFF_FORMAT_NAME |
-		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY))))
-		die(_("-L does not yet support the requested diff format"));
+		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY |
+		DIFF_FORMAT_NUMSTAT | DIFF_FORMAT_DIFFSTAT |
+		DIFF_FORMAT_SHORTSTAT))))
+		die(_("-L does not support the requested diff format"));
 
 	if (revs->expand_tabs_in_log < 0)
 		revs->expand_tabs_in_log = revs->expand_tabs_in_log_default;
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 233dc232e3..4e8f71c289 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -176,24 +176,9 @@ test_expect_success '--name-status shows status and path' '
 	test_grep ! "^@@" actual
 '
 
-test_expect_success '--stat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --stat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--numstat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --numstat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--shortstat is not yet supported with -L' '
-	test_must_fail git log -L1,24:b.c --shortstat 2>err &&
-	test_grep "does not yet support" err
-'
-
-test_expect_success '--dirstat is not yet supported with -L' '
+test_expect_success '--dirstat is not supported with -L' '
 	test_must_fail git log -L1,24:b.c --dirstat 2>err &&
-	test_grep "does not yet support" err
+	test_grep "does not support" err
 '
 
 test_expect_success 'setup for checking fancy rename following' '
@@ -793,9 +778,9 @@ test_expect_success '-L with -S suppresses non-matching commits' '
 	test_cmp expect actual
 '
 
-test_expect_success '--full-diff is not yet supported with -L' '
+test_expect_success '--full-diff is not supported with -L' '
 	test_must_fail git log -L1,24:b.c --full-diff 2>err &&
-	test_grep "does not yet support" err
+	test_grep "does not support" err
 '
 
 test_expect_success '-L --oneline has no extra blank line before diff' '
@@ -806,6 +791,113 @@ test_expect_success '-L --oneline has no extra blank line before diff' '
 	test_grep "^diff --git" line2
 '
 
+test_expect_success 'setup for -L stat tests' '
+	git checkout --orphan stat-range &&
+	git reset --hard &&
+	cat >file.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int tracked_fn()
+	{
+	    return F2;
+	}
+	EOF
+	git add file.c &&
+	test_tick &&
+	git commit -m "Add func1() and tracked_fn()" &&
+
+	# Modify both functions so whole-file stats (2 added, 2 deleted)
+	# differ from the tracked range of tracked_fn (1 and 1).
+	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" file.c >tmp &&
+	mv tmp file.c &&
+	git commit -a -m "Modify both functions"
+'
+
+test_expect_success '-L --numstat limits counts to the tracked range' '
+	git log -L:tracked_fn:file.c --numstat --format=%s >actual &&
+	cat >expect <<-\EOF &&
+	Modify both functions
+
+	1	1	file.c
+	Add func1() and tracked_fn()
+
+	4	0	file.c
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '-L --stat and --shortstat limit counts to the tracked range' '
+	git log -L:tracked_fn:file.c --stat --format=%s -1 >actual &&
+	cat >expect <<-\EOF &&
+	Modify both functions
+
+	 file.c | 2 +-
+	 1 file changed, 1 insertion(+), 1 deletion(-)
+	EOF
+	test_cmp expect actual &&
+
+	git log -L:tracked_fn:file.c --shortstat --format=%s -1 >actual &&
+	cat >expect <<-\EOF &&
+	Modify both functions
+
+	 1 file changed, 1 insertion(+), 1 deletion(-)
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '--numstat across renames and multiple commits' '
+	# parallel-change carries the tracked function f across an a.c -> b.c
+	# rename and a merge of two parallel histories.
+	git checkout parallel-change &&
+	git log -M -L ":f:b.c" --format= --numstat >actual &&
+	cat >expect <<-\EOF &&
+	1	1	b.c
+	1	1	a.c
+	1	1	a.c
+	1	1	a.c
+	1	0	a.c
+	13	0	a.c
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '-L multiple ranges with --numstat excludes untracked change' '
+	git checkout --orphan multi-range &&
+	git reset --hard &&
+	cat >m.c <<-\EOF &&
+	int tracked_func1()
+	{
+	    return F1;
+	}
+
+	int tracked_func2()
+	{
+	    return F2;
+	}
+
+	int func3()
+	{
+	    return F3;
+	}
+	EOF
+	git add m.c &&
+	test_tick &&
+	git commit -m "add m.c" &&
+	sed -e "s/F1/F1 + 1/" -e "s/F2/F2 + 2/" -e "s/F3/F3 + 3/" m.c >tmp &&
+	mv tmp m.c &&
+	git commit -a -m "Modify all three functions" &&
+	git log -L:tracked_func1:m.c -L:tracked_func2:m.c --numstat --format=%s -1 >actual &&
+	cat >expect <<-\EOF &&
+	Modify all three functions
+
+	2	2	m.c
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success '--summary shows new file on root commit' '
 	git checkout parent-oids &&
 	git log -L:func2:file.c --summary --format= >actual &&
-- 
gitgitgadget

[PATCH v3 6/7] diff: support --check with -L line ranges

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Reuse the line_range_filter in builtin_checkdiff() so -L supports
the --check option.

Add orig_hunk_fn field similar to orig_line_fn that forwards
xdiff_emit_hunk_fn calls when we flush filtered hunks. This is necessary
because --check relies on receiving calls to its checkdiff_consume_hunk
function for managing state.

Document and ungate the newly enabled option, and add tests verifying
the new behavior.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc | 11 ++--
 diff.c                                | 43 +++++++++++++-
 revision.c                            |  2 +-
 t/t4211-line-log.sh                   | 83 +++++++++++++++++++++++++++
 4 files changed, 130 insertions(+), 9 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index b3e8b5c62c..4a7ab97d75 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -10,11 +10,12 @@
 	You can specify this option more than once. Implies `--patch`.
 	Patch output can be suppressed using `--no-patch`.
 	The following non-patch diff formats are supported: `--raw`,
-	`--name-only`, `--name-status`, `--summary`, `--stat`, `--numstat`,
-	and `--shortstat`. The stat formats count only lines within the tracked
-	range. `--dirstat` is not supported with `-L`: it summarizes change as each
-	directory's share of the total churn, not as counts for the tracked lines.
-	Use `--numstat` for exact per-file counts within the range.
+	`--name-only`, `--name-status`, `--summary`, `--check`, `--stat`,
+	`--numstat`, and `--shortstat`. The stat formats count only lines
+	within the tracked range. `--dirstat` is not supported with `-L`: it
+	reports how change is distributed across directories over whole files,
+	which is not meaningful for line ranges within a file. Use `--numstat`
+	for exact per-file counts within the range.
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
diff --git a/diff.c b/diff.c
index 4a30d7b631..49b6732c81 100644
--- a/diff.c
+++ b/diff.c
@@ -614,6 +614,7 @@ struct emit_callback {
  */
 struct line_range_filter {
 	xdiff_emit_line_fn orig_line_fn;
+	xdiff_emit_hunk_fn orig_hunk_fn;
 	void *orig_cb_data;
 	const struct range_set *range_sets_to_filter_by;
 	unsigned int range_set_idx;
@@ -2577,6 +2578,13 @@ static void flush_range_hunk(struct line_range_filter *filter)
 			       filter->accumulating_hunk.func_name,
 			filter->accumulating_hunk.func_name_len);
 
+	if (filter->orig_hunk_fn)
+		filter->orig_hunk_fn(filter->orig_cb_data,
+				filter->accumulating_hunk.old_begin, old_count,
+				filter->accumulating_hunk.new_begin, new_count,
+				filter->accumulating_hunk.func_name,
+		       filter->accumulating_hunk.func_name_len);
+
 	filter->ret = filter->orig_line_fn(filter->orig_cb_data, hdr.buf, hdr.len);
 	strbuf_release(&hdr);
 
@@ -4203,11 +4211,23 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 	diff_free_filespec_data(two);
 }
 
+static int idx_in_ranges(const struct range_set *ranges, long idx)
+{
+	unsigned int i;
+
+	for (i = 0; i < ranges->nr; i++)
+		if (idx >= ranges->ranges[i].start &&
+		    idx < ranges->ranges[i].end)
+			return 1;
+	return 0;
+}
+
 static void builtin_checkdiff(const char *name_a, const char *name_b,
 			      const char *attr_path,
 			      struct diff_filespec *one,
 			      struct diff_filespec *two,
-			      struct diff_options *o)
+			      struct diff_options *o,
+			      const struct range_set *line_ranges)
 {
 	mmfile_t mf1, mf2;
 	struct checkdiff_t data;
@@ -4247,7 +4267,19 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 		memset(&xecfg, 0, sizeof(xecfg));
 		xecfg.ctxlen = 1; /* at least one context line */
 		xpp.flags = 0;
-		if (xdi_diff_outf(&mf1, &mf2, checkdiff_consume_hunk,
+
+		if (line_ranges) {
+			struct line_range_filter lr_filter;
+
+			line_range_filter_init(&lr_filter, line_ranges,
+					       checkdiff_consume, &data);
+			lr_filter.orig_hunk_fn = checkdiff_consume_hunk;
+
+			if (line_range_filter_diff(&lr_filter, &mf1, &mf2,
+						   &xpp, &xecfg))
+				die("unable to generate checkdiff for %s",
+				    one->path);
+		} else if (xdi_diff_outf(&mf1, &mf2, checkdiff_consume_hunk,
 				  checkdiff_consume, &data,
 				  &xpp, &xecfg))
 			die("unable to generate checkdiff for %s", one->path);
@@ -4260,6 +4292,10 @@ static void builtin_checkdiff(const char *name_a, const char *name_b,
 			check_blank_at_eof(&mf1, &mf2, &ecbdata);
 			blank_at_eof = ecbdata.blank_at_eof_in_postimage;
 
+			if (blank_at_eof && line_ranges &&
+			    !idx_in_ranges(line_ranges, blank_at_eof - 1))
+				blank_at_eof = 0;
+
 			if (blank_at_eof) {
 				static char *err;
 				if (!err)
@@ -5055,7 +5091,8 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 	diff_fill_oid_info(p->one, o->repo->index);
 	diff_fill_oid_info(p->two, o->repo->index);
 
-	builtin_checkdiff(name, other, attr_path, p->one, p->two, o);
+	builtin_checkdiff(name, other, attr_path, p->one, p->two, o,
+			  p->line_ranges);
 }
 
 void repo_diff_setup(struct repository *r, struct diff_options *options)
diff --git a/revision.c b/revision.c
index 4639c0df8e..4cc0d032bc 100644
--- a/revision.c
+++ b/revision.c
@@ -3231,7 +3231,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 		DIFF_FORMAT_RAW | DIFF_FORMAT_NAME |
 		DIFF_FORMAT_NAME_STATUS | DIFF_FORMAT_SUMMARY |
 		DIFF_FORMAT_NUMSTAT | DIFF_FORMAT_DIFFSTAT |
-		DIFF_FORMAT_SHORTSTAT))))
+		DIFF_FORMAT_SHORTSTAT | DIFF_FORMAT_CHECKDIFF))))
 		die(_("-L does not support the requested diff format"));
 
 	if (revs->expand_tabs_in_log < 0)
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 4e8f71c289..2a542aa643 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -924,4 +924,87 @@ test_expect_success 'get_commit_action() does not mutate a not-yet-walked commit
 	)
 '
 
+test_expect_success 'setup for --check test' '
+	git checkout --orphan check-test &&
+	git reset --hard &&
+	cat >check.c <<-\EOF &&
+	void tracked()
+	{
+	    return;
+	}
+
+	void other()
+	{
+	    return;
+	}
+	EOF
+	git add check.c &&
+	test_tick &&
+	git commit -m "add check.c" &&
+	sed "s/return;/return; /" check.c >check.c.tmp &&
+	mv check.c.tmp check.c &&
+	git commit -a -m "introduce trailing whitespace"
+'
+
+test_expect_success '--check is limited to tracked ranges and reports real file line numbers' '
+	test_must_fail git log -L:tracked:check.c --check --format= >raw &&
+	grep -E ":[0-9]+:" raw >actual &&
+	echo "check.c:3: trailing whitespace." >expect &&
+	test_cmp expect actual &&
+
+	test_must_fail git log -L:tracked:check.c -L:other:check.c \
+		--check --format= >raw &&
+	grep -E ":[0-9]+:" raw >actual &&
+	cat >expect <<-\EOF &&
+	check.c:3: trailing whitespace.
+	check.c:8: trailing whitespace.
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '--check reports each error at its real line across a gap in one range' '
+	git checkout --orphan check-gap &&
+	git reset --hard &&
+	cat >gap.c <<-\EOF &&
+	void tracked()
+	{
+	    int a = 1;
+	    int b = 2;
+	    int c = 3;
+	    int d = 4;
+	    int e = 5;
+	    int g = 7;
+	    return;
+	}
+	EOF
+	git add gap.c &&
+	test_tick &&
+	git commit -m "add gap.c" &&
+	sed -e "s/int a = 1;/int a = 1; /" -e "s/int g = 7;/int g = 7; /" gap.c >tmp &&
+	mv tmp gap.c &&
+	git commit -a -m "ws errors with a gap" &&
+	test_must_fail git log -L:tracked:gap.c --check --format= >raw &&
+	grep -E ":[0-9]+:" raw >actual &&
+	cat >expect <<-\EOF &&
+	gap.c:3: trailing whitespace.
+	gap.c:8: trailing whitespace.
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '--check does not report blank-at-eof outside the range' '
+	git checkout --orphan check-eof &&
+	git reset --hard &&
+	printf "void tracked()\n{\n    return;\n}\n\nint tail = 1;\n" >eof.c &&
+	git add eof.c &&
+	test_tick &&
+	git commit -m "add eof.c" &&
+	printf "void tracked()\n{\n    return; \n}\n\nint tail = 1;\n\n" >eof.c &&
+	git commit -a -m "ws in range, blank at eof out of range" &&
+	test_must_fail git log -L:tracked:eof.c --check --format= >raw &&
+	grep -E ":[0-9]+:" raw >actual &&
+	echo "eof.c:3: trailing whitespace." >expect &&
+	test_cmp expect actual
+'
+
 test_done
-- 
gitgitgadget

[PATCH v3 7/7] diffcore-pickaxe: limit -G to the -L tracked range

[Michael Montalbo via GitGitGadget]

From: Michael Montalbo <mmontalbo@gmail.com>

Teach -G to only search the line ranges specified by -L.
Teaching -S is left as future work, so it still matches the entire
file even if -L is specified.

Rather than being part of diff.c's builtin implementations, the
diffcore-pickaxe functionality interacts with xdiff-interface as a
separate component. Add a sibling to xdi_diff_outf(), called
diff_emit_line_ranges(), that limits emitted lines to the given line
ranges.

Use diff_emit_line_ranges() when searching text if line ranges have
been specified. If textconv is enabled, use normal diffing instead of
diff_emit_line_ranges() since line range tracking relies on the line
coordinates of the original, pre-textconv file.

Update documentation and add tests accordingly.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
---
 Documentation/line-range-options.adoc |  4 +-
 diff.c                                | 11 ++++
 diffcore-pickaxe.c                    | 30 ++++++++--
 t/t4211-line-log.sh                   | 81 ++++++++++++++++++++++-----
 xdiff-interface.h                     | 10 ++++
 5 files changed, 115 insertions(+), 21 deletions(-)

diff --git a/Documentation/line-range-options.adoc b/Documentation/line-range-options.adoc
index 4a7ab97d75..52e1262fd7 100644
--- a/Documentation/line-range-options.adoc
+++ b/Documentation/line-range-options.adoc
@@ -19,6 +19,8 @@
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
-as are pickaxe options (`-S`, `-G`) and `--diff-filter`.
+as are pickaxe options (`-S`, `-G`) and `--diff-filter`. `-G` is
+limited to the tracked range. In contrast, `-S` is evaluated over the whole
+file and may select a commit with a change outside the tracked range.
 +
 include::line-range-format.adoc[]
diff --git a/diff.c b/diff.c
index 49b6732c81..1a3571d229 100644
--- a/diff.c
+++ b/diff.c
@@ -2701,6 +2701,17 @@ static int line_range_filter_diff(struct line_range_filter *filter,
 	return ret;
 }
 
+int diff_emit_line_ranges(mmfile_t *one, mmfile_t *two,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	struct line_range_filter filter;
+
+	line_range_filter_init(&filter, ranges, line_fn, cb_data);
+	return line_range_filter_diff(&filter, one, two, xpp, xecfg);
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index b0915be86f..2425fe8101 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -16,7 +16,8 @@
 
 typedef int (*pickaxe_fn)(mmfile_t *one, mmfile_t *two,
 			  struct diff_options *o,
-			  regex_t *regexp, kwset_t kws);
+			  regex_t *regexp, kwset_t kws,
+			  const struct range_set *ranges);
 
 struct diffgrep_cb {
 	regex_t *regexp;
@@ -42,7 +43,8 @@ static int diffgrep_consume(void *priv, char *line, unsigned long len)
 
 static int diff_grep(mmfile_t *one, mmfile_t *two,
 		     struct diff_options *o,
-		     regex_t *regexp, kwset_t kws UNUSED)
+		     regex_t *regexp, kwset_t kws UNUSED,
+		     const struct range_set *ranges)
 {
 	struct diffgrep_cb ecbdata;
 	xpparam_t xpp;
@@ -65,8 +67,12 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	 * An xdiff error might be our "data->hit" from above. See the
 	 * comment for xdiff_emit_line_fn in xdiff-interface.h
 	 */
-	ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
-			    &ecbdata, &xpp, &xecfg);
+	if (ranges)
+		ret = diff_emit_line_ranges(one, two, ranges, diffgrep_consume,
+					    &ecbdata, &xpp, &xecfg);
+	else
+		ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
+				    &ecbdata, &xpp, &xecfg);
 	if (ecbdata.hit)
 		return 1;
 	if (ret)
@@ -119,8 +125,13 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws,
 
 static int has_changes(mmfile_t *one, mmfile_t *two,
 		       struct diff_options *o UNUSED,
-		       regex_t *regexp, kwset_t kws)
+		       regex_t *regexp, kwset_t kws,
+		       const struct range_set *ranges UNUSED)
 {
+	/*
+	 * -S counts needle occurrences in each whole blob. Limiting this to
+	 * an -L range is left as a follow-up; for now -S ignores the range.
+	 */
 	unsigned int c1 = one ? contains(one, regexp, kws, 0) : 0;
 	unsigned int c2 = two ? contains(two, regexp, kws, c1 + 1) : 0;
 	return c1 != c2;
@@ -132,6 +143,7 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	struct userdiff_driver *textconv_one = NULL;
 	struct userdiff_driver *textconv_two = NULL;
 	mmfile_t mf1, mf2;
+	const struct range_set *ranges;
 	int ret;
 
 	/* ignore unmerged */
@@ -169,7 +181,13 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	mf1.size = fill_textconv(o->repo, textconv_one, p->one, &mf1.ptr);
 	mf2.size = fill_textconv(o->repo, textconv_two, p->two, &mf2.ptr);
 
-	ret = fn(&mf1, &mf2, o, regexp, kws);
+	/*
+	 * -L limits the search to the tracked range, but the range is in
+	 * pre-textconv line coordinates that do not map onto textconv
+	 * output, so search the whole file when textconv is enabled.
+	 */
+	ranges = (textconv_one || textconv_two) ? NULL : p->line_ranges;
+	ret = fn(&mf1, &mf2, o, regexp, kws, ranges);
 
 	if (textconv_one)
 		free(mf1.ptr);
diff --git a/t/t4211-line-log.sh b/t/t4211-line-log.sh
index 2a542aa643..2354400d1c 100755
--- a/t/t4211-line-log.sh
+++ b/t/t4211-line-log.sh
@@ -703,24 +703,18 @@ test_expect_success '-L suppresses deletions outside tracked range' '
 	test $(grep -c "^diff --git" actual) = 1
 '
 
-test_expect_success '-L with -S filters to string-count changes' '
+test_expect_success '-L with -S selects only the matching commit' '
 	git checkout parent-oids &&
-	git log -L:func2:file.c -S "F2 + 2" --format= >actual &&
-	# -S searches the whole file, not just the tracked range;
-	# combined with the -L range walk, this selects commits that
-	# both touch func2 and change the count of "F2 + 2" in the file.
-	test $(grep -c "^diff --git" actual) = 1 &&
-	test_grep "F2 + 2" actual
+	git log -L:func2:file.c -S "F2 + 2" --format=%s --no-patch >actual &&
+	echo "Modify func2() in file.c" >expect &&
+	test_cmp expect actual
 '
 
-test_expect_success '-L with -G filters to diff-text matches' '
+test_expect_success '-L with -G selects only the matching commit' '
 	git checkout parent-oids &&
-	git log -L:func2:file.c -G "F2 [+] 2" --format= >actual &&
-	# -G greps the whole-file diff text, not just the tracked range;
-	# combined with -L, this selects commits that both touch func2
-	# and have "F2 + 2" in their diff.
-	test $(grep -c "^diff --git" actual) = 1 &&
-	test_grep "F2 + 2" actual
+	git log -L:func2:file.c -G "F2 [+] 2" --format=%s --no-patch >actual &&
+	echo "Modify func2() in file.c" >expect &&
+	test_cmp expect actual
 '
 
 test_expect_success 'setup for trailing deletion test' '
@@ -1007,4 +1001,63 @@ test_expect_success '--check does not report blank-at-eof outside the range' '
 	test_cmp expect actual
 '
 
+test_expect_success '-L -G is limited to the tracked range' '
+	git checkout --orphan grep-range &&
+	git reset --hard &&
+	cat >gp.c <<-\EOF &&
+	int func1()
+	{
+	    return ALPHA;
+	}
+
+	int func2()
+	{
+	    return BETA;
+	}
+	EOF
+	git add gp.c &&
+	test_tick &&
+	git commit -m "add gp.c" &&
+	sed -e "s/ALPHA/ALPHA2/" -e "s/BETA/BETA2/" gp.c >tmp &&
+	mv tmp gp.c &&
+	git commit -a -m "touch both functions" &&
+	git log -L:func2:gp.c -G BETA --format=%s --no-patch >actual &&
+	cat >expect <<-\EOF &&
+	touch both functions
+	add gp.c
+	EOF
+	test_cmp expect actual &&
+	git log -L:func2:gp.c -G ALPHA --format=%s --no-patch >actual &&
+	test_must_be_empty actual
+'
+
+test_expect_success '-L -G searches the whole file under textconv' '
+	git checkout --orphan grep-textconv &&
+	git reset --hard &&
+	cat >tc.c <<-\EOF &&
+	int func1()
+	{
+	    return F1;
+	}
+
+	int func2()
+	{
+	    return F2;
+	}
+	EOF
+	git add tc.c &&
+	test_tick &&
+	git commit -m "add tc.c" &&
+	sed -e "s/F1/F1 + 1/" -e "s/return F2/return FINDME/" tc.c >tmp &&
+	mv tmp tc.c &&
+	git commit -a -m "change both funcs" &&
+	echo "tc.c diff=tc" >.gitattributes &&
+	git log -L:func1:tc.c -G FINDME --format=%s --no-patch >actual &&
+	test_must_be_empty actual &&
+	git config diff.tc.textconv cat &&
+	git log -L:func1:tc.c -G FINDME --format=%s --no-patch >actual &&
+	echo "change both funcs" >expect &&
+	test_cmp expect actual
+'
+
 test_done
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 2428456629..4151bc2097 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -46,6 +46,16 @@ int xdi_diff_outf(mmfile_t *mf1, mmfile_t *mf2,
 		  xdiff_emit_line_fn line_fn,
 		  void *consume_callback_data,
 		  xpparam_t const *xpp, xdemitconf_t const *xecfg);
+
+struct range_set;
+/*
+ * Like xdi_diff_outf(), but forwards only the lines within the given
+ * postimage line ranges to line_fn.
+ */
+int diff_emit_line_ranges(mmfile_t *mf1, mmfile_t *mf2,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg);
 int read_mmfile(mmfile_t *ptr, const char *filename);
 void read_mmblob(mmfile_t *ptr, struct object_database *odb,
 		 const struct object_id *oid);
-- 
gitgitgadget