builtin/stash: report failure to write to index

The git-stash(1) command needs to write to the index for many of its
operations. When the index is locked by a concurrent writer it will thus
fail to operate, which is expected. What is not expected though is that
we do not print any error message at all in this case. The user can thus
easily miss the fact that the command didn't do what they expected it to
do and would be left wondering why that is.

Fix this bug and report failures to write to the index. Add tests for
the subcommands which hit the respective code paths.

While at it, unify error messages when writing to the index fails. The
chosen error message is already used in "builtin/stash.c".

Reported-by: moti sd <motisd8@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 56 insertions, 4 deletions

diff --git a/builtin/stash.c b/builtin/stash.c
index 4a6771c9f4..5c6ed02313 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -521,7 +521,7 @@ static void unstage_changes_unless_new(struct object_id *orig_tree)
 	repo_hold_locked_index(the_repository, &lock, LOCK_DIE_ON_ERROR);
 	if (write_locked_index(&the_index, &lock,
 			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
-		die(_("Unable to write index."));
+		die(_("could not write index"));
 }
 
 static int do_apply_stash(const char *prefix, struct stash_info *info,
@@ -538,7 +538,7 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
 	repo_read_index_preload(the_repository, NULL, 0);
 	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET, 0, 0,
 					 NULL, NULL, NULL))
-		return -1;
+		return error(_("could not write index"));
 
 	if (write_index_as_tree(&c_tree, &the_index, get_index_file(), 0,
 				NULL))
@@ -1365,7 +1365,7 @@ static int do_create_stash(const struct pathspec *ps, struct strbuf *stash_msg_b
 	repo_read_index_preload(the_repository, NULL, 0);
 	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET, 0, 0,
 					 NULL, NULL, NULL) < 0) {
-		ret = -1;
+		ret = error(_("could not write index"));
 		goto done;
 	}
 
@@ -1556,7 +1556,7 @@ static int do_push_stash(const struct pathspec *ps, const char *stash_msg, int q
 
 	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET, 0, 0,
 					 NULL, NULL, NULL)) {
-		ret = -1;
+		ret = error(_("could not write index"));
 		goto done;
 	}
 
diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
index 34faeac3f1..3caf490e39 100755
--- a/t/t3903-stash.sh
+++ b/t/t3903-stash.sh
@@ -1516,4 +1516,56 @@ test_expect_success 'restore untracked files even when we hit conflicts' '
 	)
 '
 
+test_expect_success 'stash create reports a locked index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A A.file &&
+		echo change >A.file &&
+		touch .git/index.lock &&
+
+		cat >expect <<-EOF &&
+		error: could not write index
+		EOF
+		test_must_fail git stash create 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'stash push reports a locked index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A A.file &&
+		echo change >A.file &&
+		touch .git/index.lock &&
+
+		cat >expect <<-EOF &&
+		error: could not write index
+		EOF
+		test_must_fail git stash push 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'stash apply reports a locked index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A A.file &&
+		echo change >A.file &&
+		git stash push &&
+		touch .git/index.lock &&
+
+		cat >expect <<-EOF &&
+		error: could not write index
+		EOF
+		test_must_fail git stash apply 2>err &&
+		test_cmp expect err
+	)
+'
+
 test_done