[PATCH] peel_onion(): add support for <rev>^{tag}

[Richard Hansen <rhansen@bbn.com>]

gitrevisions(7) implies that <rev>^{tag} should work, but before now
it did not:

    $ git rev-parse --verify v1.8.3.1^{tag}
    fatal: Needed a single revision

This commit fixes the omission:

    $ git rev-parse --verify v1.8.3.1^{tag}
    4bc068950abec778a02ebf3ee73cf0735affabb4

Other object type names work as expected:

    $ git rev-parse --verify v1.8.3.1^{commit}
    362de916c06521205276acb7f51c99f47db94727
    $ git rev-parse --verify v1.8.3.1^{tree}
    c1fef48675edd74e9af19405339e8bdaebd56b0c
    $ git rev-parse --verify v1.8.3.1^{blob}
    error: v1.8.3.1^{blob}: expected blob type, but the object dereferences to tree type
    fatal: Needed a single revision

Note that <rev>^{tag} is not the same as <rev>^{object} when <rev> is
not a tag:

    $ git rev-parse --verify v1.8.3.1^{}^{object}
    362de916c06521205276acb7f51c99f47db94727
    $ git rev-parse --verify v1.8.3.1^{}^{tag}
    error: v1.8.3.1^{}^{tag}: expected tag type, but the object dereferences to tree type
    fatal: Needed a single revision

Signed-off-by: Richard Hansen <rhansen@bbn.com>
---
 sha1_name.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sha1_name.c b/sha1_name.c
index 90419ef..68fd0e4 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -677,6 +677,8 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 	sp++; /* beginning of type name, or closing brace for empty */
 	if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
 		expected_type = OBJ_COMMIT;
+	else if (!strncmp(tag_type, sp, 3) && sp[3] == '}')
+		expected_type = OBJ_TAG;
 	else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
 		expected_type = OBJ_TREE;
 	else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
-- 
1.8.3.1