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

["Michael Montalbo via GitGitGadget" <gitgitgadget@gmail.com>]

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 &&
-- 
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