The filtered checkout we used before was a nice idea, but only worked
for small numbers of commits in a PR. It would fetch the whole history
initially, but only fetch objects on demand. This turns out to be much
too slow in a PR with 18 commits, regularly hitting the 10 minute
timeout, even when running it locally.
The new approach uses regular checkouts again. In contrast to the old
style, before we switched to the filtered checkout, this only fetches
exactly the commits we need - and all of them at once. This is
significantly faster than both other approaches, and scales much better.
A bigger number of commits doesn't have much of an effect, if any at
all.
This broke when we moved the check-cherry-picks workflow into the bigger
PR workflow. At this time, the "workflow run" became the whole PR
workflow, which includes many more than just 1 job, thus the assumption
in `jobs[0]` doesn't hold anymore.
Most of the checks we do for cherry-picks are dismissable warnings, with
one exception: When a commit hash has been found, but this hash is not
available in any of the pickable branches, we raise this with
severity=error. This should also *block* the merge and not be
dismissable. That's because this is a fixable issue in every case.
Previously, when the diff contained a context line with ```, this would
end the code block and entirely break the markdown rendering.
Now we use the html code blocks provided by `core.summary` and properly
escape the content, so that it never escapes via html tags.
This reduces noise that the cherry-pick reviews produce when formatting
related conflicts had to be resolved. We only do this in the
length-limited review comment, though. All changes, including
whitespace, can still be double-checked in the job log if needed.
This turns the check-cherry-pick script into a github-script based
JavaScript program. This makes it much easier to extend to check reverts
or merge commits later on.
