Migrate compare_source_branch to use only Gitaly

What does this MR do?

Migrates another method to Gitaly, through a client side only migration.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

gitaly#771 (closed)

added 1 commit

• d65db552 - Migrate compare_source_branch to use only Gitaly

Compare with previous version

assigned to @jacobvosmaer-gitlab

LGTM! Provided it works and tests pass. :)

assigned to @zj

assigned to @smcgivern

Thanks @zj, one question.

assigned to @zj

assigned to @smcgivern

resolved all discussions

approved this merge request

merged

mentioned in commit 4666ef68

mentioned in issue gitaly#1222 (closed)

mentioned in issue gitaly#1228 (closed)

@zj @smcgivern FYI this change seems to have broken one spec in EE: https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/74590673. I fixed it by adding the :repository trait to the factory project we're using in ee/spec/services/merge_requests/build_service_spec.rb. That was done as part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6110.

That said, I find it a bit suspect that I had to make this change... 🤔

@rymai thanks! I think before this must have failed silently; your fix makes sense to me.

mentioned in issue gitlab-org/release/tasks#302 (closed)

mentioned in issue #38689 (moved)

added devopscreate groupgitaly labels