HEAD and namespaces

[Bryan Turner <bturner@atlassian.com>]

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
agent=git/2.20.1
19:51:54.013017 pkt-line.c:80           packet:          git<
b9acca03606d4c674be8b7e79cd788cedbec957c refs/heads/master
19:51:54.013028 pkt-line.c:80           packet:          git< 0000
19:51:54.013035 pkt-line.c:80           packet:          git> 0000
b9acca03606d4c674be8b7e79cd788cedbec957c HEAD
b9acca03606d4c674be8b7e79cd788cedbec957c refs/heads/master

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. Either
way, since the clone can't find the HEAD value (either because it
doesn't see "refs/namespaces/foo/HEAD" as HEAD, which I'd assume is
the case, or because it can't find
"refs/namespaces/foo/refs/heads/master"), it falls back on the old
behavior of picking the first branch with a matching commit. That
brings back all the "wrong branch" issues with cloning that adding
"symref"  fixed.

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.

Any insight would be greatly appreciated!

Bryan