After discussion with al & rco, conclusion was default PR merging method
should be rebase-and-merge for cleaner history.
Add test for that scenario (w/ test for final DAG) and implement this
change.
* avoid fetching PRs for un-managed branches if we know up-front
* avoid processing comments with no commands (avoids fetching the
corresponding PR which we know nothing about yet and which may or
may not be for a managed branch)
The old "sync pr" thing is turning out to be a bust, while it
originally worked fine these days it's a catastrophe as the v4 API
performances seem to have significantly degraded, to the point that
fetching all 15k PRs by pages of 100 simply blows up after a few
hundreds/thousands.
Instead, add a table of PRs to sync: if we get notified of a
"compatible" PR (enabled repo & target) which we don't know of, create
an entry in a "fetch jobs" table, then a cron will handle fetching the
PR then fetching/applying all relevant metadata (statuses,
review-comments and reviews).
Also change indexation of Commit(sha) and PR(head) to hash, as btree
indexes are not really sensible for such content (the ordering is
unhelpful and the index locality is awful by design/definition).
Previously when splitting staging we'd create two never-staged
stagings. In a system where the stagings get deleted once done
with (succeeeded or failed) that's not really important, but now that
we want to keep stagings around inactive things get problematic as
this method gunks up the stagings table, plus the post-split stagings
would "steal" the original's batches, losing information (relation
between stagings and batches).
Replace these empty stagings with dedicated *split* objects. A batch
can belong to both a staging and a split, the split is deleted once a
new staging has been created from it.
Eventually we may want to make batches shared between stagings (so we
can track the entire history of a batch) but currently that's only
PR-level.
If we want a dashboard with a history of stagings, maybe not deleting
them would be a good idea.
A replacement for the headless stagings would probably be a good idea:
currently they're created when splitting a failed staging containing
more than one batch, but their only purpose is as splits of existing
batches to be deactivated/deleted to be re-staged (new batches &
stagings are created then as e.g. some of the batches may not be
merge-able anymore) and that's a bit weird.
AL thinks it's not useful and it's better to always squash/rebase a
single commit & merge multiple. Mark tests as xfail'd instead of
removing them.
Also mark test_edit_retarget_managed as skipped explicitly
* p0 cancel existing stagings in order to be staged as soon as
possible
* p0 PRs should be picked over split batches
* p0 bypass PR-level CI and review requirements
* p0 can be set on any of a batch's PR, matched PRs will be staged
alongside even if their priority is the default
