refs/merge-requests not updated in target repo when source branch is updated

The problem

When an update is made to a branch that is the source branch for an open merge request, the corresponding ref in .git/refs/merge-requests in the target repository is not updated.

Explanation

Whenever a new merge request is created a new ref is created in the target repository under .git/refs/merge-requests that points to the current head of the source branch for the merge. Gitlab does the equivalent of the following from the target repository:

git fetch source_repo refs/heads/my_new_feature:refs/merge-requests/X/head

where the X would be replaced with the ID of the merge request within the target repo.

If changes are now added to branch my_new_feature the new objects automatically get fetched to the target repository (and in the web UI the merge request is updated), but the refs/merge-requests/X/head is not updated.

This is due to the fact that in merge_requests_controller.rb the method ensure_ref_fetched of the MergeRequest model is used. This means that the ref is only fetched from the source repo if refs/merge-requests/X/head does not exist.

Expected behaviour

I would expect that refs/merge-requests/X/head always points to the most up-to date version of the source branch. This seems reasonable, as otherwise anyone using a CLI workflow will not have the most up-to date version of the merge request. In addition, if the target repo is pruned at any point, then the commits added after the merge request was opened will disappear from the target repo.

Title changed from refs/merge-requests not updated in target repo when source branch is updated to refs/merge-requests not updated in target repo when source branch is updated

We encounter the same behavior here. With 8.0 it worked though and so it must have been a change made with 8.1. This is really a big blocker for us as we're using Jenkins with the GitLab Plugin (little bit modified) to work with the new merge-request references. But as they will never be updated, we cannot switch over to this.

I see two ways of potentially solving this:

1. Make RefreshService update the ref every time the source branch changes.
2. Use a symbolic ref to point refs/merge-requests/X/head to the source branch.

@dzaporozhets, what do you think?

@stanhu I think option 1 with updating ref every time source branch changes is best solution

Added ~12980 label

Milestone changed to 8.2

It would be nice to fix as people actually expect this behavior

mentioned in merge request !1683 (merged)

Let me know if !1683 (merged) does the trick.

This bug is blocking a new subscriber from migrating their projects completely. https://gitlab.zendesk.com/agent/tickets/10588

Added ~113220 label

For everyone playing at home, @pbouillet had a chance to test out !1683 (merged) before the -f option was added to git fetch. It turns out -f is necessary since if you rebase and force push, git fetch won't do anything (from https://git-scm.com/docs/git-fetch):

When git fetch is used with : refspec, it refuses to update the local branch unless the remote branch it fetches is a descendant of . This option overrides that check.

I think adding the force flag makes sense.

Thanks for adding the flag @stanhu!

Is it already set that this change won't make it into some kind of hotfix release for 8.1 and will only be available with 8.2?

I'll add it to the list of 8.1 regressions and leave that to @JobV and @rspeicher to decide. :)

mentioned in issue #3078 (closed)

Thanks

Status changed to closed by merge request !1683 (merged)

Status changed to closed by commit f56c7d9f

mentioned in issue #3259 (closed)

mentioned in commit f56c7d9f

mentioned in commit f24324ad

mentioned in commit 38039e3a