Subject: [PATCH v3 3/5] diff: teach "--stat -w --exit-code" to notice differences

From: Junio C Hamano <[email-masked]>
Date: Fri, 18 Aug 2023 16:59:30 -0700

When options like "-w" is used while "--exit-code" option is in
effect, instead of the usual "do we have any filepair whose preimage
and postimage have different <mode,object>?" check, we need to compare
the contents of the blobs, taking into account that certain changes
are considered no-op.

With the previous step, we taught "--patch" codepath to set the
.found_changes bit correctly, even for a change that only affects
the mode and not object.  The "--stat" codepath, however, did not
set the .found_changes bit at all.  This lead to

    $ git diff --stat -w --exit-code

for a change that does have an output to exit with status 0.

Set the bit by inspecting the list of paths the diffstat output is
given for (a mode-only change will still appear as a "0-line added
0-line deleted" change) to fix it.

Signed-off-by: Junio C Hamano <[email-masked]>
---
 diff.c                     | 1 +
 t/t4015-diff-whitespace.sh | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/diff.c b/diff.c
index 998d7ae20c..da965ff688 100644
--- a/diff.c
+++ b/diff.c
@@ -6901,6 +6901,7 @@ void compute_diffstat(struct diff_options *options,
 		if (check_pair_status(p))
 			diff_flush_stat(p, options, diffstat);
 	}
+	options->found_changes = !!diffstat->nr;
 }
 
 void diff_addremove(struct diff_options *options,
diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index 02731dccb9..230a89b951 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -11,7 +11,7 @@ TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff.sh
 
-for opts in --patch --quiet -s
+for opts in --patch --quiet -s --stat --shortstat --dirstat=lines
 do
 
 	test_expect_success "status with $opts (different)" '
-- 
2.42.0-rc2-7-gf9972720e9