dir.c: ignore paths containing .git when invalidating untracked cache

read_directory() code ignores all paths named ".git" even if it's not
a valid git repository. See treat_path() for details. Since ".git" is
basically invisible to read_directory(), when we are asked to
invalidate a path that contains ".git", we can safely ignore it
because the slow path would not consider it anyway.

This helps when fsmonitor is used and we have a real ".git" repo at
worktree top. Occasionally .git/index will be updated and if the
fsmonitor hook does not filter it, untracked cache is asked to
invalidate the path ".git/index".

Without this patch, we invalidate the root directory unncessarily,
which:

- makes read_directory() fall back to slow path for root directory
  (slower)

- makes the index dirty (because UNTR extension is updated). Depending
  on the index size, writing it down could also be slow.

A note about the new "safe_path" knob. Since this new check could be
relatively expensive, avoid it when we know it's not needed. If the
path comes from the index, it can't contain ".git". If it does
contain, we may be screwed up at many more levels, not just this one.

Noticed-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
index eb2d13bbcf..756beb0d8e 100755
--- a/t/t7519-status-fsmonitor.sh
+++ b/t/t7519-status-fsmonitor.sh
@@ -314,4 +314,43 @@ test_expect_success 'splitting the index results in the same state' '
 	test_cmp expect actual
 '
 
+test_expect_success UNTRACKED_CACHE 'ignore .git changes when invalidating UNTR' '
+	test_create_repo dot-git &&
+	(
+		cd dot-git &&
+		mkdir -p .git/hooks &&
+		: >tracked &&
+		: >modified &&
+		mkdir dir1 &&
+		: >dir1/tracked &&
+		: >dir1/modified &&
+		mkdir dir2 &&
+		: >dir2/tracked &&
+		: >dir2/modified &&
+		write_integration_script &&
+		git config core.fsmonitor .git/hooks/fsmonitor-test &&
+		git update-index --untracked-cache &&
+		git update-index --fsmonitor &&
+		GIT_TRACE_UNTRACKED_STATS="$TRASH_DIRECTORY/trace-before" \
+		git status &&
+		test-dump-untracked-cache >../before
+	) &&
+	cat >>dot-git/.git/hooks/fsmonitor-test <<-\EOF &&
+	printf ".git\0"
+	printf ".git/index\0"
+	printf "dir1/.git\0"
+	printf "dir1/.git/index\0"
+	EOF
+	(
+		cd dot-git &&
+		GIT_TRACE_UNTRACKED_STATS="$TRASH_DIRECTORY/trace-after" \
+		git status &&
+		test-dump-untracked-cache >../after
+	) &&
+	grep "directory invalidation" trace-before >>before &&
+	grep "directory invalidation" trace-after >>after &&
+	# UNTR extension unchanged, dir invalidation count unchanged
+	test_cmp before after
+'
+
 test_done