In most cases, fetching the remote HEAD explicitly is
unnecessary. It's just a symref pointing to a branch which
we are already fetching, so we will already ask for its sha1.
However, if the remote has a detached HEAD, things are less
certain. We do not ask for HEAD's sha1, but we do try to
write it into a local detached HEAD. In most cases this is
fine, as the remote HEAD is pointing to some part of the
history graph that we will fetch via the refs.
But if the remote HEAD points to an "orphan" commit (one
which was is not an ancestor of any refs), then we will not
have the object, and update_ref will complain when we try to
write the detached HEAD, aborting the whole clone.
This patch makes clone always explicitly ask the remote for
the sha1 of its HEAD commit. In the non-detached case, this
is a no-op, as we were going to ask for that sha1 anyway. In
the regular detached case, this will add an extra "want" to
the protocol negotiation, but will not change the history
that gets sent. And in the detached orphan case, we will
fetch the orphaned history so that we can write it into our
local detached HEAD.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The guess_remote_head function tries to figure out where a
remote's HEAD is pointing by comparing the sha1 of the
remote's HEAD with the sha1 of various refs found on the
remote. However, we were too liberal in matching refs, and
would match tags or remote tracking branches, even though
these things could not possibly be referenced by the HEAD
symbolic ref (since git will detach when checking them out).
As a result, a clone of a remote repository with a detached
HEAD might write "refs/tags/*" into our local HEAD, which is
bogus. The resulting HEAD should be detached.
The other related code path is remote.c's get_head_names()
(which is used for, among other things, "set-head -a"). This was
not affected, however, as that function feeds only refs from
refs/heads to guess_remote_head.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We didn't test this setup at all, and doing so reveals a few
bugs:
1. Cloning a repository with an orphaned detached HEAD
(i.e., one that points to history that is not
referenced by any ref) will fail.
2. Cloning a repository with a detached HEAD that points
to a tag will cause us to write a bogus "refs/tags/..."
ref into the HEAD symbolic ref. We should probably
detach instead.
3. Cloning a repository with a detached HEAD that points
to a branch will cause us to checkout that branch. This
is a known limitation of the git protocol (we have to
guess at HEAD's destination, since the symref contents
aren't shown to us). This test serves to document the
desired behavior, which can only be achieved once the
git protocol learns to share symref information.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
