Follow-up from "MR unmergeable notification"

It would be nice to detect MR conflicts when the conflict is introduced, not when a user or reviewer visit MR's page. If possible we could check if MR is mergeable when target branch changes. A potential performance issue - question is how expensive is checking status for all pending MRs for the given target branch.

The following discussion from gitlab-ce!18042 should be addressed:

• @jprovaznik started a discussion: (+2 comments)

  @lulalala I'm struggling to test this behavior, when I try this scenario:

  • create a MR with target branch master (same source/target project)
  • this MR has can_be_merged status
  • then I push some conflicting changes into the master branch
  • when these changes are pushed to master, the MR switches to its status to unchecked
  • no email is sent to the author of the MR

  I would expect that the MR would be checked if it's mergeable when there are changes in the target branch. Or does this MR addresses different scenario?