Revert "Revert "Merge branch '18193-developers-can-merge' into 'master'""

What does this MR do?

Reverts the revert of !4892 (merged) which lacked an EE MR at the time. This has been done in gitlab-org/gitlab-ee!564.

What are the relevant issue numbers?

Closes #19872 (closed).

/cc @timothyandrew

mentioned in issue #19872 (closed)

Specs are not failing locally... :/

Reassigned to @timothyandrew

I'm waiting for this to be merged so that I can add docs in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5269.

@axil Cool!

@timothyandrew Any findings so far?

mentioned in merge request !5269 (closed)

@rymai Nothing yet, but I'm able to reproduce it locally with just:

$ spring rspec spec/services/merge_requests/update_service_spec.rb

@rymai: I just figured this out - turns out that this MR creates a lock_version column on the merge_requests table, which implicitly enables optimistic locking. IIRC, this was introduced while I was rebasing the feature branch against master at some point.

In any case, I'll push the fix asap.

/cc @axil

mentioned in commit de1fa501

Build should be fixed in de1fa501.

Added 1 commit:

• de1fa501 - Remove lock_version from the merge_requests table.

@timothyandrew Thanks, nice catch!

Reassigned to @rymai

@rymai Build is green.

@timothyandrew Awesome, thank you!

Status changed to merged

mentioned in commit 08264f43

Added ~149423 label