This simulates the state of the repository after the PR is
rebased-and-merged into the target branch and validates the merged
result rather than the PR branch in isolation.
Without this step, CI may run against a stale branch. A PR that merges
cleanly can still fail verification after merging into target because
the target branch may have advanced and changed tests. Conversely, the
Docker image used for the build may no longer work with the old
repository state when testing an old PR branch. This also allows the PR
to be revalidated by simply rerunning CI, without requiring an explicit
rebase.
This change also fails CI early when rebase conflicts are detected. Since
PRs with conflicts cannot be merged, there is no value in running the
remaining verification steps.
This is bit strict as it likely will fail to rebase merge commits,
should they be present in the PR. However, we generally prefer linear
history. It's rebased mostly to avoid search for merge commit in target
branch. While for PR we can ask API how many commit there are and the
parent of that should be merge-base commit, for target branch it's
unknown how deep this common commit is. It would be trivial if we did
full non-shallow clone, but we do shallow and probably want to keep it
this way. This forces us to just replay commits from PR on the tip of
the current target branch. It's fine, this is what we want in the end of
the day.
Incidentally this also fixes recently merged
dd6ae3e024, which tries to validate commit
messages, but by default clone depth is 1 so only single commit message
of head commit in PR was merged. After this change all commits will be
visible. However, I still liked the API script that we had before, not
sure why this was completely reworked.
Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
Kacper Michajłow
14ed5e8ae3