The test-only script for GitLab CI does not reliably use the right commit

This might be easy. From git help fetch:

The format of a parameter is an optional plus +, followed
by the source , followed by a colon :, followed by the
destination ref . The colon can be omitted when is
empty. is typically a ref, but it can also be a fully spelled
hex object name.

Does $CI_MERGE_REQUEST_DIFF_BASE_SHA mean what I think it does? All I see on https://docs.gitlab.com/ee/ci/variables/predefined_variables.html is that it is defined only for merge request pipelines (while the merge request is open), that it has been available since GitLab 13.7 on all CI runners, and it is described as

The base SHA of the merge request diff.

The 3416154-test-only-correct-commit branch contains the changes that I think should fix this issue. I have not yet made a MR from that branch.

The test-only-do-not-commit branch contains those changes and also changes one of the tests in the migrate module. That should be enough to test this issue.

From https://git.drupalcode.org/issue/drupal-3416154/-/jobs/670143:

warning: refname '18125a4619bc8b7f2b2adf89e85b4743bd06deb5' is ambiguous.
Git normally never creates a ref that ends with 40 hex characters
because it will be ignored when you just specify 40-hex. These refs
may be created by mistake. For example,
git switch -c $br $(git rev-parse ...)
where "$br" is somehow empty and a 40-hex ref is created. Please
examine these refs and maybe delete them. Turn this message off by
running "git config advice.objectNameWarning false"

That message is repeated several times.

I think this works. See the issue summary for the two MRs.

Test-only job with expected failure and updated info messages: https://git.drupalcode.org/issue/drupal-3416154/-/jobs/670275

BTW, both branch names include "test-only". That refers to the CI job (and the related script). It does not mean that the MR is only for testing. I apologize for any confusion.

@benjifisher

posted about this on in #gitlab and the response I got was

Commit: https://git.drupalcode.org/project/drupal/-/commit/e1312a3d8b1205882847b...
Issue: https://www.drupal.org/project/drupal/issues/3418207 🐛 Spell-checking job fails with "couldn't find remote ref refs/heads/11.x" when 11.x branch does not exist in fork Active
Follow-up: https://www.drupal.org/project/drupal/issues/3419182 🐛 Test-only job fails with "couldn't find remote ref refs/heads/11.x" when 11.x branch does not exist in fork Needs review (it’s RTBC)
so if that follow-up RTBCed issue gets merged, the one on this thread might not be needed

Could you confirm?

In the issue summary, I mentioned that this issue is a follow-up to 📌 Make CI template compatible with private repositories Fixed . I am adding that as a related issue.

Thanks for the link to 🐛 Test-only job fails with "couldn't find remote ref refs/heads/11.x" when 11.x branch does not exist in fork Needs review . I think that is a duplicate of this issue, but if that is already RTBC, we can close this one when it gets fixed. I am adding it as another related issue.

🐛 Test-only job fails with "couldn't find remote ref refs/heads/11.x" when 11.x branch does not exist in fork Needs review landed!