Mark MR as merged regardless of errors when closing issues

We should mark the MR as merged as first thing on PostMergeService as in practice it is already merged on the repository. Happens that errors may happen when executing external services such as Issues::CloseService, and we do not want a MR hanging as opened because of that.

app/services/merge_requests/post_merge_service.rb

@@ -6,9 +6,9 @@ module MergeRequests
   #
   class PostMergeService < MergeRequests::BaseService
     def execute(merge_request)
+      merge_request.mark_as_merged
       close_issues(merge_request)
       todo_service.merge_merge_request(merge_request, current_user)
-      merge_request.mark_as_merged
       create_event(merge_request)
       create_note(merge_request)
       notification_service.merge_mr(merge_request, current_user)

changelogs/unreleased/osw-mark-as-merged-as-first-post-merge-action.yml

+---
+title: Mark MR as merged regardless of errors when closing issues
+merge_request:
+author:
+type: fixed

spec/services/merge_requests/post_merge_service_spec.rb

@@ -47,5 +47,18 @@ describe MergeRequests::PostMergeService do
 
       expect(diff_removal_service).to have_received(:execute)
     end
+
+    it 'marks MR as merged regardless of errors when closing issues' do
+      merge_request.update(target_branch: 'foo')
+      allow(project).to receive(:default_branch).and_return('foo')
+
+      issue = create(:issue, project: project)
+      allow(merge_request).to receive(:closes_issues).and_return([issue])
+      allow_any_instance_of(Issues::CloseService).to receive(:execute).with(issue, commit: merge_request).and_raise
+
+      expect { described_class.new(project, user, {}).execute(merge_request) }.to raise_error
+
+      expect(merge_request.reload).to be_merged
+    end
   end
 end