[PATCH v2] describe: refresh the index when 'broken' flag is used

[Abhijeet Sonar <abhijeet.nkt@gmail.com>]

When describe is run with 'dirty' flag, we refresh the index
to make sure it is in sync with the filesystem before
determining if the working tree is dirty.  However, this is
not done for the codepath where the 'broken' flag is used.

This causes `git describe --broken --dirty` to false
positively report the worktree being dirty if a file has
different stat info than what is recorded in the index.
Running `git update-index -q --refresh` to refresh the index
before running diff-index fixes the problem.

Also add tests to deliberately update stat info of a
file before running describe to verify it behaves correctly.

Reported-by: Paul Millar <paul.millar@desy.de>
Suggested-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Abhijeet Sonar <abhijeet.nkt@gmail.com>
---
 builtin/describe.c  | 12 ++++++++++++
 t/t6120-describe.sh | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/builtin/describe.c b/builtin/describe.c
index e5287eddf2..3e751f1239 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -53,6 +53,10 @@ static const char *diff_index_args[] = {
 	"diff-index", "--quiet", "HEAD", "--", NULL
 };
 
+static const char *update_index_args[] = {
+	"update-index", "--unmerged", "-q", "--refresh", NULL
+};
+
 struct commit_name {
 	struct hashmap_entry entry;
 	struct object_id peeled;
@@ -645,6 +649,14 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 	if (argc == 0) {
 		if (broken) {
 			struct child_process cp = CHILD_PROCESS_INIT;
+			struct child_process update_index_cp = CHILD_PROCESS_INIT;
+
+			strvec_pushv(&update_index_cp.args, update_index_args);
+			update_index_cp.git_cmd = 1;
+			update_index_cp.no_stdin = 1;
+			update_index_cp.no_stdout = 1;
+			run_command(&update_index_cp);
+
 			strvec_pushv(&cp.args, diff_index_args);
 			cp.git_cmd = 1;
 			cp.no_stdin = 1;
diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
index e78315d23d..ac781a7b52 100755
--- a/t/t6120-describe.sh
+++ b/t/t6120-describe.sh
@@ -671,4 +671,36 @@ test_expect_success 'setup misleading taggerdates' '
 
 check_describe newer-tag-older-commit~1 --contains unique-file~2
 
+test_expect_success 'describe --dirty with a file with changed stat' '
+	git init stat-dirty &&
+	cd stat-dirty &&
+
+	echo A >file &&
+	git add file &&
+	git commit -m A &&
+	git tag A -a -m A &&
+
+	cat file >file.new &&
+	mv file.new file &&
+	git describe --dirty >actual &&
+	echo "A" >expected &&
+	test_cmp expected actual
+'
+
+test_expect_success 'describe --dirty --broken with a file with changed stat' '
+	git init stat-dirty-broken &&
+	cd stat-dirty-broken &&
+
+	echo A >file &&
+	git add file &&
+	git commit -m A &&
+	git tag A -a -m A &&
+
+	cat file >file.new &&
+	mv file.new file &&
+	git describe --dirty --broken >actual &&
+	echo "A" >expected &&
+	test_cmp expected actual
+'
+
 test_done
-- 
2.45.2.606.g9005149a4a.dirty