Subject: [PATCH] diff: disabled quick optimization with --find-copies-harder

From: René Scharfe <[email-masked]>
Date: Sun, 9 Nov 2025 13:11:39 +0100

If --find-copies-harder is given, diff-lib.c::show_modified() queues
even non-modified entries using diff_change() because we need them for
copy detection.  diff_change() sets flags.has_changes, though.  If
--quiet is also given this causes diff_can_quit_early() to declare we're
done after seeing only the very first entry, which is way too soon.
Disable this optimization in that case.

This issue is hidden without --no-ext-diff because then we set
flags.diff_from_contents, which disables the optimization in a
different way.

Reported-by: D. Ben Knoble <[email-masked]>
Signed-off-by: René Scharfe <[email-masked]>
---
 diff.c              |  1 +
 t/t4007-rename-3.sh | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/diff.c b/diff.c
index a1961526c0..84ac148c37 100644
--- a/diff.c
+++ b/diff.c
@@ -7188,6 +7188,7 @@ int diff_can_quit_early(struct diff_options *opt)
 {
 	return (opt->flags.quick &&
 		!opt->filter &&
+		!opt->flags.find_copies_harder &&
 		opt->flags.has_changes);
 }
 
diff --git a/t/t4007-rename-3.sh b/t/t4007-rename-3.sh
index e8faf0dd2e..3fc81bcd76 100755
--- a/t/t4007-rename-3.sh
+++ b/t/t4007-rename-3.sh
@@ -41,6 +41,16 @@ test_expect_success 'copy detection, cached' '
 	compare_diff_raw current expected
 '
 
+test_expect_success 'exit code of quiet copy detection' '
+	test_expect_code 1 \
+	git diff --quiet --cached --find-copies-harder $tree
+'
+
+test_expect_success 'exit code of quiet copy detection with --no-ext-diff' '
+	test_expect_code 1 \
+	git diff --quiet --cached --find-copies-harder --no-ext-diff $tree
+'
+
 # In the tree, there is only path0/COPYING.  In the cache, path0 and
 # path1 both have COPYING and the latter is a copy of path0/COPYING.
 # However when we say we care only about path1, we should just see
-- 
2.51.2