Makefile: start fixing regression in c75c02f5
Start fixing the regressions in c75c02f5 (Makefile: Do not re-clone repos when rebuilding git/libgit2, 2021-02-17) noted in [A]. What I said in that comment:
This breaks e.g. upgrading from v2.29.0 to v2.29.1.
There's multiple bugs here:
1. The clone is --depth=1, but not the fetch, so if you need to bump a
version we switch to a full clone
2. You do e.g. "git fetch v2.29.1", but this does not create a
refs/tags/v2.29.1 locally, we just put it into FETCH_HEAD, this is
unlike the clone --branch option. Thus upgrading a version will
fetch it successfully, but then we die on the "switch".
3. You're doing rev-parse --verify <thing>^{tree}. Presumably to not
pass a full SHA-1, why not just cat-file -t <thing>? I tried
fixing #1 (closed) by instead doing --no-tags <obj>:<obj> but that
fails with trying to write a tag into refs/heads/. As an aside I
think that's a bug in git's fetching logic, it should pick
refs/tags/* as the local namespace in that case.
Then writing everything into refs/tags/*. But now e.g. if you specify
some SHA-1 it's just happenstance whether it works, did we slurp it
down in the initial clone?This starts to fix at least some of that. Now if we see a new version we're going to create a refs/tags/* name for it (even if it's e.g. "master").
The --no-tags option is needed because that option really doesn't mean "no tags", it means "don't do tag following". Without it the "--depth 1" is pretty pointless.
This is still going to be buggy in the case where you specify e.g. "master" but that ref has moved.