Merge branch 'jc/index-update-if-able' into maint

* jc/index-update-if-able:
  update $GIT_INDEX_FILE when there are racily clean entries
  diff/status: refactor opportunistic index update

builtin/commit.c

@@ -1131,13 +1131,8 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, s.pathspec, NULL, NULL);
 
 	fd = hold_locked_index(&index_lock, 0);
-	if (0 <= fd) {
-		if (active_cache_changed &&
-		    !write_cache(fd, active_cache, active_nr))
-			commit_locked_index(&index_lock);
-		else
-			rollback_lock_file(&index_lock);
-	}
+	if (0 <= fd)
+		update_index_if_able(&the_index, &index_lock);
 
 	s.is_initial = get_sha1(s.reference, sha1) ? 1 : 0;
 	s.in_merge = in_merge;

builtin/diff.c

@@ -197,12 +197,7 @@ static void refresh_index_quietly(void)
 	discard_cache();
 	read_cache();
 	refresh_cache(REFRESH_QUIET|REFRESH_UNMERGED);
-
-	if (active_cache_changed &&
-	    !write_cache(fd, active_cache, active_nr))
-		commit_locked_index(lock_file);
-
-	rollback_lock_file(lock_file);
+	update_index_if_able(&the_index, lock_file);
 }
 
 static int builtin_diff_files(struct rev_info *revs, int argc, const char **argv)

cache.h

@@ -527,6 +527,7 @@ extern NORETURN void unable_to_lock_index_die(const char *path, int err);
 extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
 extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
 extern int commit_lock_file(struct lock_file *);
+extern void update_index_if_able(struct index_state *, struct lock_file *);
 
 extern int hold_locked_index(struct lock_file *, int);
 extern int commit_locked_index(struct lock_file *);

read-cache.c

@@ -1568,6 +1568,31 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce)
 	return result;
 }
 
+static int has_racy_timestamp(struct index_state *istate)
+{
+	int entries = istate->cache_nr;
+	int i;
+
+	for (i = 0; i < entries; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		if (is_racy_timestamp(istate, ce))
+			return 1;
+	}
+	return 0;
+}
+
+/*
+ * Opportunisticly update the index but do not complain if we can't
+ */
+void update_index_if_able(struct index_state *istate, struct lock_file *lockfile)
+{
+	if ((istate->cache_changed || has_racy_timestamp(istate)) &&
+	    !write_index(istate, lockfile->fd))
+		commit_locked_index(lockfile);
+	else
+		rollback_lock_file(lockfile);
+}
+
 int write_index(struct index_state *istate, int newfd)
 {
 	git_SHA_CTX c;