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[PATCH v5] diff: ensure consistent diff behavior with ignore options

From
Lidong Yan <yldhome2d2@gmail.com>
Date
Aug 8, 2025, 03:30 UTC
Message-ID
<20250808033019.78817-1-yldhome2d2@gmail.com>
In-Reply-To
<AC10362A-5B05-47D0-98CF-DE6AD468F01D@gmail.com>

In git-diff, options like `-w` and `-I<regex>`, two files are considered equivalent under the specified "ignore" rules, even when they are not bit-for-bit identical. For options like `--raw`, `--name-status`, and `--name-only`, git-diff deliberately compares only the SHA values to determine whether two files are equivalent, for performance reasons. As a result, a file shown in `git diff --name-status` may not appear in `git diff --patch`.

To quickly determine whether two files are equivalent, add a helper function diff_flush_patch_quietly() in diff.c. Add `.dry_run` field in `struct diff_options`. When `.dry_run` is true, builtin_diff() returns immediately upon finding any change. Call diff_flush_patch_quietly() to determine if we should flush `--raw`, `--name-only` or `--name-status` output.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Lidong Yan <yldhome2d2@gmail.com>
---
 diff.c                     | 64 +++++++++++++++++++++++++++++---------
 diff.h                     |  2 ++
 t/t4013-diff-various.sh    | 13 ++++++++
 t/t4015-diff-whitespace.sh |  8 ++---
 xdiff-interface.h          |  6 ++--
 5 files changed, 70 insertions(+), 23 deletions(-)
diff --git a/diff.c b/diff.c
index dca87e164f..cb04a9a6f2 100644
--- a/diff.c
+++ b/diff.c
@@ -2444,6 +2444,15 @@ static int fn_out_consume(void *priv, char *line, unsigned long len)
 	return 0;
 }
 
+static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED)
+{
+	struct emit_callback *ecbdata = priv;
+	struct diff_options *o = ecbdata->opt;
+
+	o->found_changes = 1;
+	return 1;
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
@@ -3759,8 +3768,21 @@ static void builtin_diff(const char *name_a,
 
 		if (o->word_diff)
 			init_diff_words_data(&ecbdata, o, one, two);
-		if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
-				  &ecbdata, &xpp, &xecfg))
+		if (o->dry_run) {
+			/*
+			 * Unlike the !dry_run case, we need to ignore the
+			 * return value from xdi_diff_outf() here, because
+			 * xdi_diff_outf() takes non-zero return from its
+			 * callback function as a sign of error and returns
+			 * early (which is why we return non-zero from our
+			 * callback, quick_consume()).  Unfortunately,
+			 * xdi_diff_outf() signals an error by returning
+			 * non-zero.
+			 */
+			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
+				      &ecbdata, &xpp, &xecfg);
+		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
+					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
 		if (o->word_diff)
 			free_diff_words_data(&ecbdata);
@@ -6150,6 +6172,22 @@ static void diff_flush_patch(struct diff_filepair *p, struct diff_options *o)
 	run_diff(p, o);
 }
 
+/* return 1 if any change is found; otherwise, return 0 */
+static int diff_flush_patch_quietly(struct diff_filepair *p, struct diff_options *o)
+{
+	int saved_dry_run = o->dry_run;
+	int saved_found_changes = o->found_changes;
+	int ret;
+
+	o->dry_run = 1;
+	o->found_changes = 0;
+	diff_flush_patch(p, o);
+	ret = o->found_changes;
+	o->dry_run = saved_dry_run;
+	o->found_changes |= saved_found_changes;
+	return ret;
+}
+
 static void diff_flush_stat(struct diff_filepair *p, struct diff_options *o,
 			    struct diffstat_t *diffstat)
 {
@@ -6778,8 +6816,15 @@ void diff_flush(struct diff_options *options)
 			     DIFF_FORMAT_CHECKDIFF)) {
 		for (i = 0; i < q->nr; i++) {
 			struct diff_filepair *p = q->queue[i];
-			if (check_pair_status(p))
-				flush_one_pair(p, options);
+
+			if (!check_pair_status(p))
+				continue;
+
+			if (options->flags.diff_from_contents &&
+			    !diff_flush_patch_quietly(p, options))
+				continue;
+
+			flush_one_pair(p, options);
 		}
 		separator++;
 	}
@@ -6831,19 +6876,10 @@ void diff_flush(struct diff_options *options)
 	if (output_format & DIFF_FORMAT_NO_OUTPUT &&
 	    options->flags.exit_with_status &&
 	    options->flags.diff_from_contents) {
-		/*
-		 * run diff_flush_patch for the exit status. setting
-		 * options->file to /dev/null should be safe, because we
-		 * aren't supposed to produce any output anyway.
-		 */
-		diff_free_file(options);
-		options->file = xfopen("/dev/null", "w");
-		options->close_file = 1;
-		options->color_moved = 0;
 		for (i = 0; i < q->nr; i++) {
 			struct diff_filepair *p = q->queue[i];
 			if (check_pair_status(p))
-				diff_flush_patch(p, options);
+				diff_flush_patch_quietly(p, options);
 			if (options->found_changes)
 				break;
 		}
diff --git a/diff.h b/diff.h
index 62e5768a9a..91b3e1c5cf 100644
--- a/diff.h
+++ b/diff.h
@@ -400,6 +400,8 @@ struct diff_options {
 	#define COLOR_MOVED_WS_ERROR (1<<0)
 	unsigned color_moved_ws_handling;
 
+	bool dry_run;
+
 	struct repository *repo;
 	struct strmap *additional_path_headers;
 
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 8ebd170451..cfeec239e0 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -648,6 +648,19 @@ test_expect_success 'diff -I<regex>: detect malformed regex' '
 	test_grep "invalid regex given to -I: " error
 '
 
+test_expect_success 'diff -I<regex>: ignore matching file' '
+	test_when_finished "git rm -f file1" &&
+	test_seq 50 >file1 &&
+	git add file1 &&
+	test_seq 50 | sed -e "s/13/ten and three/" -e "s/^[124-9].*/& /" >file1 &&
+
+	: >actual &&
+	git diff --raw --ignore-blank-lines -I"ten.*e" -I"^[124-9]" >>actual &&
+	git diff --name-only --ignore-blank-lines -I"ten.*e" -I"^[124-9]" >>actual &&
+	git diff --name-status --ignore-blank-lines -I"ten.*e" -I"^[124-9]" >>actual &&
+	test_grep ! "file1" actual
+'
+
 # check_prefix <patch> <src> <dst>
 # check only lines with paths to avoid dependency on exact oid/contents
 check_prefix () {
diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index 52e3e476ff..9de7f73f42 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -11,12 +11,8 @@ test_description='Test special whitespace in diff engine.
 . "$TEST_DIRECTORY"/lib-diff.sh
 
 for opt_res in --patch --quiet -s --stat --shortstat --dirstat=lines \
-	       --raw! --name-only! --name-status!
+	       --raw --name-only --name-status
 do
-	opts=${opt_res%!} expect_failure=
-	test "$opts" = "$opt_res" ||
-		expect_failure="test_expect_code 1"
-
 	test_expect_success "status with $opts (different)" '
 		echo foo >x &&
 		git add x &&
@@ -43,7 +39,7 @@ do
 		echo foo >x &&
 		git add x &&
 		echo " foo" >x &&
-		$expect_failure git diff -w $opts --exit-code x
+		git diff -w $opts --exit-code x
 	'
 done
 
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 1ed430b622..dfc55daddf 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -28,9 +28,9 @@
  * from an error internal to xdiff, xdiff itself will see that
  * non-zero return and translate it to -1.
  *
- * See "diff_grep" in diffcore-pickaxe.c for a trick to work around
- * this, i.e. using the "consume_callback_data" to note the desired
- * early return.
+ * See "diff_grep" in diffcore-pickaxe.c and "quick_consume" in diff.c
+ * for a trick to work around this, i.e. using the "consume_callback_data"
+ * to note the desired early return.
  */
 typedef int (*xdiff_emit_line_fn)(void *, char *, unsigned long);
 typedef void (*xdiff_emit_hunk_fn)(void *data,

-- 
2.39.5 (Apple Git-154)
Previous: Lidong YanNext: Johannes Schindelin
Message 34 of 35 in “git-diff: --ignore-matching-lines has no effect on the output when --name-only is used”
  1. hi@arnes.spaceJul 23, 2025
  2. Lidong YanJul 23, 2025
  3. Junio C HamanoJul 23, 2025
  4. Lidong YanJul 24, 2025
  5. Eric SunshineJul 24, 2025
  6. Lidong YanJul 24, 2025
  7. hi@arnes.spaceJul 25, 2025
  8. hi@arnes.spaceJul 25, 2025
  9. Lidong YanJul 25, 2025
  10. hi@arnes.spaceJul 25, 2025
  11. Jeff KingJul 25, 2025
  12. Junio C HamanoJul 25, 2025
  13. diff: ensure consistent diff behavior with -I<regex> across output formatsLidong Yan, Jul 29, 2025
  14. Junio C HamanoJul 30, 2025
  15. Jeff KingAug 2, 2025
  16. Lidong YanAug 3, 2025
  17. Junio C HamanoAug 3, 2025
  18. Junio C HamanoAug 4, 2025
  19. Jeff KingAug 4, 2025
  20. diff: ensure consistent diff behavior with -I<regex> across output formatsLidong Yan, Aug 3, 2025
  21. Junio C HamanoAug 4, 2025
  22. Lidong YanAug 4, 2025
  23. Junio C HamanoAug 4, 2025
  24. Lidong YanAug 5, 2025
  25. Junio C HamanoAug 5, 2025
  26. diff: ensure consistent diff behavior with ignore optionsLidong Yan, Aug 6, 2025
  27. Junio C HamanoAug 6, 2025
  28. Lidong YanAug 7, 2025
  29. Junio C HamanoAug 6, 2025
  30. Lidong YanAug 7, 2025
  31. diff: ensure consistent diff behavior with ignore optionsLidong Yan, Aug 7, 2025
  32. Junio C HamanoAug 7, 2025
  33. Lidong YanAug 8, 2025
  34. diff: ensure consistent diff behavior with ignore optionsLidong Yan, Aug 8, 2025
  35. Johannes SchindelinOct 16, 2025

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