Teach git-describe to use peeled ref information when scanning tags

By using the peeled ref information inside of the packed-refs file we
can avoid opening tag objects to obtain the commits they reference.
This speeds up git-describe when there are a large number of tags
in the repository as we have less objects to parse before we can
start commit matching.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-describe.c b/builtin-describe.c
index 3428483134156f4e1761aa47ed2e8098a294808c..bfd25e232454d977e2ad1b9e68ab6ff4c739381d 100644 (file)
--- a/builtin-describe.c
+++ b/builtin-describe.c
@@ -46,19 +46,30 @@ static void add_to_known_names(const char *path,
 
 static int get_name(const char *path, const unsigned char *sha1, int flag, void *cb_data)
 {
-       struct commit *commit = lookup_commit_reference_gently(sha1, 1);
+       struct commit *commit;
        struct object *object;
-       int prio;
+       unsigned char peeled[20];
+       int is_tag, prio;
+
+       if (!peel_ref(path, peeled) && !is_null_sha1(peeled)) {
+               commit = lookup_commit_reference_gently(peeled, 1);
+               if (!commit)
+                       return 0;
+               is_tag = !!hashcmp(sha1, commit->object.sha1);
+       } else {
+               commit = lookup_commit_reference_gently(sha1, 1);
+               object = parse_object(sha1);
+               if (!commit || !object)
+                       return 0;
+               is_tag = object->type == OBJ_TAG;
+       }
 
-       if (!commit)
-               return 0;
-       object = parse_object(sha1);
        /* If --all, then any refs are used.
         * If --tags, then any tags are used.
         * Otherwise only annotated tags are used.
         */
        if (!prefixcmp(path, "refs/tags/")) {
-               if (object->type == OBJ_TAG) {
+               if (is_tag) {
                        prio = 2;
                        if (pattern && fnmatch(pattern, path + 10, 0))
                                prio = 0;