[PATCH 21/21] Add fsck_verify_ref_to_tag_object() to verify that refname matches name stored in tag object

[Johan Herland <johan@herland.net>]

On Monday 28 May 2007, Junio C Hamano wrote:
> However it would be a good
> idea to add logic to fsck to warn upon inconsistencis (perhaps
> by mistake) between refname and tag's true name.
>
> The check would say something like:
>
>   If an annotated (signed or unsigned) tag has a "tag"
>   line to give it the official $name, and if it is pointed
>   at by a ref, the refname must end with "/$name".
>   Otherwise we warn.
>
> Trivially, the above rule says that having v2.6.22 tag under
> refs/tags/v2.6.20 is a mistake we would want to be warned upon.

This patch adds the check described by Junio.

It also includes a bugfix when tag object parsing fails, from
Johannes Schindelin <Johannes.Schindelin@gmx.de>.

Signed-off-by: Johan Herland <johan@herland.net>
---
 builtin-fsck.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/builtin-fsck.c b/builtin-fsck.c
index 7b4c36b..a47976c 100644
--- a/builtin-fsck.c
+++ b/builtin-fsck.c
@@ -542,6 +542,30 @@ static int fsck_handle_reflog(const char *logname, const unsigned char *sha1, in
 	return 0;
 }
 
+static void fsck_verify_ref_to_tag_object(const char *refname, struct object *obj)
+{
+	/* Verify that refname matches the name stored in obj's "tag" header */
+	struct tag *tagobj = (struct tag *) parse_object(obj->sha1);
+	size_t tagname_len;
+	size_t refname_len = strlen(refname);
+
+	if (!tagobj->tag) {
+		error("%s: Failed to parse tag object %s", refname, sha1_to_hex(obj->sha1));
+		return;
+	}
+	tagname_len = strlen(tagobj->tag);
+	if (!tagname_len) return; /* No tag name stored in tagobj. Nothing to do. */
+
+	if (tagname_len < refname_len &&
+		!memcmp(tagobj->tag, refname + (refname_len - tagname_len), tagname_len) &&
+		refname[(refname_len - tagname_len) - 1] == '/') {
+		/* OK: tag name is "$name", and refname ends with "/$name" */
+		return;
+	}
+	else
+		error("%s: Mismatch between tag ref and tag object's name: '%s'", refname, tagobj->tag);
+}
+
 static int fsck_handle_ref(const char *refname, const unsigned char *sha1, int flag, void *cb_data)
 {
 	struct object *obj;
@@ -556,6 +580,8 @@ static int fsck_handle_ref(const char *refname, const unsigned char *sha1, int f
 		/* We'll continue with the rest despite the error.. */
 		return 0;
 	}
+	if (obj->type == OBJ_TAG) /* ref to tag object */
+		fsck_verify_ref_to_tag_object(refname, obj);
 	default_refs++;
 	obj->used = 1;
 	mark_reachable(obj, REACHABLE);
-- 
1.5.2