During the 17.0 freezeathon, the freeze wizard blew up with
MergeError: merge-tree: {oid} - not something we can merge
Turns out when freezes were moved to local
(4d2c0f86e1) I forgot to fetch the heads
of the release and bump PRs into the local repo, so rebasing them atop
their branch would fail because the local repository would just not
find the object being rebased.
I had missed that case in testing as well, but in fairness even if I
had tried testing it I'd likely have missed it: implementation
limitations (shortcuts) of dummy central mean it currently ignores
what objects the client requests and bundles everything it can find
associated with the repository (meaning it sends the entire network).
This is not usually an issue because the test repos are pretty small,
but it means the client can have objects they should not because they
never requested them and might not even be supposed to be aware of
their existence.
Anyway solve by doing the obvious: fetch the heads of the release and
bump PRs at the same time we update the branch being forked off. Also
update the freeze tests to trigger the issue (by creating the release
/ bump PRs in different repos) and running the tests against github
actual to make sure we can actually see them fail (correctly, the
merge error we expect) not via errors in the test), and we do fix
them.
Fixes#821