diff-lib: fix check_removed when fsmonitor is on

`git diff-index` may return incorrect deleted entries when fsmonitor
is used in a repository with git submodules. This can be observed on
Mac machines, but it can affect all other supported platforms too.

If fsmonitor is used, `stat *st` is not initialized if cache_entry has
CE_FSMONITOR_VALID set. But, there are three call sites that rely on stat
afterwards, which can result in incorrect results.

This change partially reverts commit 4f3d6d0 (fsmonitor: skip lstat
deletion check during git diff-index, 2021-03-17).

Signed-off-by: Josip Sokcevic <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: sokcevicG

diff-lib.c

@@ -28,14 +28,14 @@
  * exists for ce that is a submodule -- it is a submodule that is not
  * checked out).  Return negative for an error.
  */
-static int check_removed(const struct index_state *istate, const struct cache_entry *ce, struct stat *st)
+static int check_removed(const struct cache_entry *ce, struct stat *st)
 {
-	assert(is_fsmonitor_refreshed(istate));
-	if (!(ce->ce_flags & CE_FSMONITOR_VALID) && lstat(ce->name, st) < 0) {
+	if (lstat(ce->name, st) < 0) {
 		if (!is_missing_file_error(errno))
 			return -1;
 		return 1;
 	}
+
 	if (has_symlink_leading_path(ce->name, ce_namelen(ce)))
 		return 1;
 	if (S_ISDIR(st->st_mode)) {
@@ -141,7 +141,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 			memset(&(dpath->parent[0]), 0,
 			       sizeof(struct combine_diff_parent)*5);
 
-			changed = check_removed(istate, ce, &st);
+			changed = check_removed(ce, &st);
 			if (!changed)
 				wt_mode = ce_mode_from_stat(ce, st.st_mode);
 			else {
@@ -221,7 +221,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 		} else {
 			struct stat st;
 
-			changed = check_removed(istate, ce, &st);
+			changed = check_removed(ce, &st);
 			if (changed) {
 				if (changed < 0) {
 					perror(ce->name);
@@ -296,7 +296,7 @@ static int get_stat_data(const struct index_state *istate,
 	if (!cached && !ce_uptodate(ce)) {
 		int changed;
 		struct stat st;
-		changed = check_removed(istate, ce, &st);
+		changed = check_removed(ce, &st);
 		if (changed < 0)
 			return -1;
 		else if (changed) {

t/t7527-builtin-fsmonitor.sh

@@ -809,6 +809,11 @@ my_match_and_clean () {
 		status --porcelain=v2 >actual.without &&
 	test_cmp actual.with actual.without &&
 
+	git -C super --no-optional-locks diff-index --name-status HEAD >actual.with &&
+	git -C super --no-optional-locks -c core.fsmonitor=false \
+		diff-index --name-status HEAD >actual.without &&
+	test_cmp actual.with actual.without &&
+
 	git -C super/dir_1/dir_2/sub reset --hard &&
 	git -C super/dir_1/dir_2/sub clean -d -f
 }