Re: HEAD and namespaces

[Jeff King <peff@peff.net>]

On Mon, May 20, 2019 at 07:59:03PM -0700, Bryan Turner wrote:

> When using GIT_NAMESPACE, it appears the "symref" added to the
> capabilities advertisement doesn't get the namespace stripped. The
> namespace is stripped for the advertised refs, including "HEAD", but
> not on the "symref".
> 
> Lafiel:test bturner$ GIT_NAMESPACE=foo GIT_TRACE_PACKET=1 git ls-remote origin
> 19:51:54.012696 pkt-line.c:80           packet:          git<
> b9acca03606d4c674be8b7e79cd788cedbec957c HEAD\0multi_ack thin-pack
> side-band side-band-64k ofs-delta shallow deepen-since deepen-not
> deepen-relative no-progress include-tag multi_ack_detailed
> symref=refs/namespaces/foo/HEAD:refs/namespaces/foo/refs/heads/master

Yeah, that seems totally broken. It's neat that we find HEAD inside the
namespace. But I think there are two bugs here:

  1. We must call it "HEAD" and not the nonsense
     refs/namespaces/foo/HEAD

  2. We need to similarly remove the namespace from its contents. I
     suppose it's possible that somebody stores the already-truncated
     name in the symref, but as you noted then such a symref would be
     totally broken from the perspective of the non-namespaced repo.

> I don't know whether the client somehow does some stripping on the
> "symref" to decide that HEAD should be
> "refs/namespaces/foo/refs/heads/master", but I'd assume not.

I don't think it can. It has no idea that namespaces are in play at all
(and the point of the feature is for it to be invisible to the client).

> Is this a bug? An oversight? An intentional decision? How is HEAD
> supposed to work when using GIT_NAMESPACE? Perhaps the expectation is
> that namespaces won't have their own HEADs? I'd say perhaps it's that
> even in the namespace the target ref shouldn't be namespaced, but that
> doesn't seem like it could possibly be correct since the namespace
> could contain refs that don't exist outside it, so Git would see the
> symbolic ref as broken.

I think it should be doing:

diff --git a/upload-pack.c b/upload-pack.c
index 24298913c0..4d2129e7fc 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -1037,8 +1037,8 @@ static int find_symref(const char *refname, const struct object_id *oid,
 	symref_target = resolve_ref_unsafe(refname, 0, NULL, &flag);
 	if (!symref_target || (flag & REF_ISSYMREF) == 0)
 		die("'%s' is a symref but it is not?", refname);
-	item = string_list_append(cb_data, refname);
-	item->util = xstrdup(symref_target);
+	item = string_list_append(cb_data, strip_namespace(refname));
+	item->util = xstrdup(strip_namespace(symref_target));
 	return 0;
 }
 

and this case has just been broken since 7171d8c15f (upload-pack: send
symbolic ref information as capability, 2013-09-17). It mostly works
because of fallback to the old guessing behavior, so nobody really
noticed. (I also suspect namespaces are not widely used at all, but I
could be wrong).

-Peff