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

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

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.

Noticed-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Sorry for the resend, I forgot git@vger.

 dir.c             | 13 ++++++++++++-
 git-compat-util.h |  2 ++
 wrapper.c         | 12 ++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/dir.c b/dir.c
index 7c4b45e30e..f8b4cabba9 100644
--- a/dir.c
+++ b/dir.c
@@ -1773,7 +1773,7 @@ static enum path_treatment treat_path(struct dir_struct *dir,
 	if (!de)
 		return treat_path_fast(dir, untracked, cdir, istate, path,
 				       baselen, pathspec);
-	if (is_dot_or_dotdot(de->d_name) || !strcmp(de->d_name, ".git"))
+	if (is_dot_or_dotdot(de->d_name) || !fspathcmp(de->d_name, ".git"))
 		return path_none;
 	strbuf_setlen(path, baselen);
 	strbuf_addstr(path, de->d_name);
@@ -2970,8 +2970,19 @@ static int invalidate_one_component(struct untracked_cache *uc,
 void untracked_cache_invalidate_path(struct index_state *istate,
 				     const char *path)
 {
+	const char *end;
+	int skipped;
+
 	if (!istate->untracked || !istate->untracked->root)
 		return;
+	if (!fspathcmp(path, ".git"))
+		return;
+	if (ignore_case)
+		skipped = skip_caseprefix(path, "/.git", &end);
+	else
+		skipped = skip_prefix(path, "/.git", &end);
+	if (skipped && (*end == '\0' || *end == '/'))
+		return;
 	invalidate_one_component(istate->untracked, istate->untracked->root,
 				 path, strlen(path));
 }
diff --git a/git-compat-util.h b/git-compat-util.h
index 68b2ad531e..27e0b761a3 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -484,6 +484,8 @@ static inline int skip_prefix(const char *str, const char *prefix,
 	return 0;
 }
 
+int skip_caseprefix(const char *str, const char *prefix, const char **out);
+
 /*
  * If the string "str" is the same as the string in "prefix", then the "arg"
  * parameter is set to the "def" parameter and 1 is returned.
diff --git a/wrapper.c b/wrapper.c
index d20356a776..bb888d9401 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -690,3 +690,15 @@ int xgethostname(char *buf, size_t len)
 		buf[len - 1] = 0;
 	return ret;
 }
+
+int skip_caseprefix(const char *str, const char *prefix, const char **out)
+{
+	do {
+		if (!*prefix) {
+			*out = str;
+			return 1;
+		}
+	} while (tolower(*str++) == tolower(*prefix++));
+
+	return 0;
+}
-- 
2.16.1.207.gedba492059