cache: add fake_lstat()

At times, we may already know that a path represented by a
cache_entry ce has no changes via some out-of-line means, like
fsmonitor, and yet need the control to go through a codepath that
requires us to have "struct stat" obtained by lstat() on the path,
for various purposes (e.g. "ie_match_stat()" wants cached stat-info
is still current wrt "struct stat", "diff" wants to know st_mode).

The callers of lstat() on a tracked file, when its cache_entry knows
it is up-to-date, can instead call this helper to pretend that it
called lstat() by faking the "struct stat" information.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/read-cache.c b/read-cache.c
index 080bd39..eb750e2 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -197,6 +197,33 @@ void fill_stat_cache_info(struct index_state *istate, struct cache_entry *ce, st
 	}
 }
 
+static unsigned int st_mode_from_ce(const struct cache_entry *ce)
+{
+	extern int trust_executable_bit, has_symlinks;
+
+	switch (ce->ce_mode & S_IFMT) {
+	case S_IFLNK:
+		return has_symlinks ? S_IFLNK : (S_IFREG | 0644);
+	case S_IFREG:
+		return (ce->ce_mode & (trust_executable_bit ? 0755 : 0644)) | S_IFREG;
+	case S_IFGITLINK:
+		return S_IFDIR | 0755;
+	case S_IFDIR:
+		return ce->ce_mode;
+	default:
+		BUG("unsupported ce_mode: %o", ce->ce_mode);
+	}
+}
+
+int fake_lstat(const struct cache_entry *ce, struct stat *st)
+{
+	fake_lstat_data(&ce->ce_stat_data, st);
+	st->st_mode = st_mode_from_ce(ce);
+
+	/* always succeed as lstat() replacement */
+	return 0;
+}
+
 static int ce_compare_data(struct index_state *istate,
 			   const struct cache_entry *ce,
 			   struct stat *st)