[WIP PATCH] diff: add option to ignore whitespaces for move detection only

[Stefan Beller <sbeller@google.com>]

Signed-off-by: Stefan Beller <sbeller@google.com>
---

 diff.c                     |  10 ++--
 diff.h                     |   1 +
 t/t4015-diff-whitespace.sh | 114 ++++++++++++++++++++++++++++++++++++++++++++-
 
See, only 10 lines of code! (and a few more for tests)

We have run out of space in diff_options.flags,touched_flags.
as we 1<<U31 as the highest bit. We could reuse 1<<9 that is currently
unused (removed in 882749a04f (diff: add --word-diff option that
generalizes --color-words, 2010-04-14)). But that postpones the
real fix for only a short amount of time.

Ideas welcome how to extend the flag space. (We cannot just make it
a long either, as some arcane architecures have 32 bit longs.)

Another TODO: documentation

I plan to trim the CC list for any resend that will be needed.

Thanks,
Stefan
 
 3 files changed, 121 insertions(+), 4 deletions(-)

diff --git a/diff.c b/diff.c
index c4a669ffa8..ddb2018307 100644
--- a/diff.c
+++ b/diff.c
@@ -726,7 +726,8 @@ static int next_byte(const char **cp, const char **endp,
 			return (int)' ';
 		}
 
-		if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE)) {
+		if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE) ||
+		    diffopt->color_moved_ignore_space) {
 			while (*cp < *endp && isspace(**cp))
 				(*cp)++;
 			/*
@@ -751,7 +752,8 @@ static int moved_entry_cmp(const struct diff_options *diffopt,
 	const char *ap = a->es->line, *ae = a->es->line + a->es->len;
 	const char *bp = b->es->line, *be = b->es->line + b->es->len;
 
-	if (!(diffopt->xdl_opts & XDF_WHITESPACE_FLAGS))
+	if (!(diffopt->xdl_opts & XDF_WHITESPACE_FLAGS) &&
+	    !diffopt->color_moved_ignore_space)
 		return a->es->len != b->es->len  || memcmp(ap, bp, a->es->len);
 
 	if (DIFF_XDL_TST(diffopt, IGNORE_WHITESPACE_AT_EOL)) {
@@ -774,7 +776,7 @@ static int moved_entry_cmp(const struct diff_options *diffopt,
 
 static unsigned get_string_hash(struct emitted_diff_symbol *es, struct diff_options *o)
 {
-	if (o->xdl_opts & XDF_WHITESPACE_FLAGS) {
+	if ((o->xdl_opts & XDF_WHITESPACE_FLAGS) || o->color_moved_ignore_space) {
 		static struct strbuf sb = STRBUF_INIT;
 		const char *ap = es->line, *ae = es->line + es->len;
 		int c;
@@ -4660,6 +4662,8 @@ int diff_opt_parse(struct diff_options *options,
 		DIFF_XDL_CLR(options, NEED_MINIMAL);
 	else if (!strcmp(arg, "-w") || !strcmp(arg, "--ignore-all-space"))
 		DIFF_XDL_SET(options, IGNORE_WHITESPACE);
+	else if (!strcmp(arg, "--ignore-all-space-in-move-detection"))
+		options->color_moved_ignore_space = 1;
 	else if (!strcmp(arg, "-b") || !strcmp(arg, "--ignore-space-change"))
 		DIFF_XDL_SET(options, IGNORE_WHITESPACE_CHANGE);
 	else if (!strcmp(arg, "--ignore-space-at-eol"))
diff --git a/diff.h b/diff.h
index aca150ba2e..6ba3f53bbd 100644
--- a/diff.h
+++ b/diff.h
@@ -196,6 +196,7 @@ struct diff_options {
 	} color_moved;
 	#define COLOR_MOVED_DEFAULT COLOR_MOVED_ZEBRA
 	#define COLOR_MOVED_MIN_ALNUM_COUNT 20
+	int color_moved_ignore_space;
 };
 
 void diff_emit_submodule_del(struct diff_options *o, const char *line);
diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index 6c9a93b734..d7ee3aabf2 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -1677,7 +1677,119 @@ test_expect_success 'move detection with submodules' '
 
 	# nor did we mess with it another way
 	git diff --submodule=diff --color | test_decode_color >expect &&
-	test_cmp expect decoded_actual
+	test_cmp expect decoded_actual &&
+	rm -rf bananas &&
+	git submodule deinit bananas
+'
+
+test_expect_success 'move detection only ignores white spaces' '
+	git reset --hard &&
+	q_to_tab <<-\EOF >function.c &&
+	int func()
+	{
+	Qif (foo) {
+	QQ// this part of the function
+	QQ// function will be very long
+	QQ// indeed. We must exceed both
+	QQ// per-line and number of line
+	QQ// minimums
+	QQ;
+	Q}
+	Qbaz();
+	Qbar();
+	Q// more unrelated stuff
+	}
+	EOF
+	git add function.c &&
+	git commit -m "add function.c" &&
+	q_to_tab <<-\EOF >function.c &&
+	int do_foo()
+	{
+	Q// this part of the function
+	Q// function will be very long
+	Q// indeed. We must exceed both
+	Q// per-line and number of line
+	Q// minimums
+	Q;
+	}
+
+	int func()
+	{
+	Qif (foo)
+	QQdo_foo();
+	Qbaz();
+	Qbar();
+	Q// more unrelated stuff
+	}
+	EOF
+
+	# Make sure we get a different diff using -w ("moved function header")
+	git diff --color --color-moved -w |
+		grep -v "index" |
+		test_decode_color >actual &&
+	q_to_tab <<-\EOF >expected &&
+	<BOLD>diff --git a/function.c b/function.c<RESET>
+	<BOLD>--- a/function.c<RESET>
+	<BOLD>+++ b/function.c<RESET>
+	<CYAN>@@ -1,6 +1,5 @@<RESET>
+	<RED>-int func()<RESET>
+	<GREEN>+<RESET><GREEN>int do_foo()<RESET>
+	 {<RESET>
+	<RED>-	if (foo) {<RESET>
+	 Q// this part of the function<RESET>
+	 Q// function will be very long<RESET>
+	 Q// indeed. We must exceed both<RESET>
+	<CYAN>@@ -8,6 +7,11 @@<RESET> <RESET>int func()<RESET>
+	 Q// minimums<RESET>
+	 Q;<RESET>
+	 }<RESET>
+	<GREEN>+<RESET>
+	<GREEN>+<RESET><GREEN>int func()<RESET>
+	<GREEN>+<RESET><GREEN>{<RESET>
+	<GREEN>+<RESET>Q<GREEN>if (foo)<RESET>
+	<GREEN>+<RESET>QQ<GREEN>do_foo();<RESET>
+	 Qbaz();<RESET>
+	 Qbar();<RESET>
+	 Q// more unrelated stuff<RESET>
+	EOF
+	test_cmp expected actual &&
+
+	# And now ignoring white space only in the move detection
+	git diff --color --color-moved --ignore-all-space-in-move-detection |
+		grep -v "index" |
+		test_decode_color >actual &&
+	q_to_tab <<-\EOF >expected &&
+	<BOLD>diff --git a/function.c b/function.c<RESET>
+	<BOLD>--- a/function.c<RESET>
+	<BOLD>+++ b/function.c<RESET>
+	<CYAN>@@ -1,13 +1,17 @@<RESET>
+	<GREEN>+<RESET><GREEN>int do_foo()<RESET>
+	<GREEN>+<RESET><GREEN>{<RESET>
+	<BOLD;CYAN>+<RESET>Q<BOLD;CYAN>// this part of the function<RESET>
+	<BOLD;CYAN>+<RESET>Q<BOLD;CYAN>// function will be very long<RESET>
+	<BOLD;CYAN>+<RESET>Q<BOLD;CYAN>// indeed. We must exceed both<RESET>
+	<BOLD;CYAN>+<RESET>Q<BOLD;CYAN>// per-line and number of line<RESET>
+	<BOLD;CYAN>+<RESET>Q<BOLD;CYAN>// minimums<RESET>
+	<BOLD;CYAN>+<RESET>Q<BOLD;CYAN>;<RESET>
+	<BOLD;CYAN>+<RESET><BOLD;CYAN>}<RESET>
+	<GREEN>+<RESET>
+	 int func()<RESET>
+	 {<RESET>
+	<RED>-Qif (foo) {<RESET>
+	<BOLD;MAGENTA>-QQ// this part of the function<RESET>
+	<BOLD;MAGENTA>-QQ// function will be very long<RESET>
+	<BOLD;MAGENTA>-QQ// indeed. We must exceed both<RESET>
+	<BOLD;MAGENTA>-QQ// per-line and number of line<RESET>
+	<BOLD;MAGENTA>-QQ// minimums<RESET>
+	<BOLD;MAGENTA>-QQ;<RESET>
+	<BOLD;MAGENTA>-Q}<RESET>
+	<GREEN>+<RESET>Q<GREEN>if (foo)<RESET>
+	<GREEN>+<RESET>QQ<GREEN>do_foo();<RESET>
+	 Qbaz();<RESET>
+	 Qbar();<RESET>
+	 Q// more unrelated stuff<RESET>
+	EOF
+	test_cmp expected actual
 '
 
 test_done
-- 
2.15.0.rc2.6.g953226eb5f