Fix auto-merge not running after discussions resolved

Previously if there were a discussion that needed to be resolved (as
determined by the project settings), the Merge When Pipeline Succeeds
would not run. Resolving the discussion would not trigger a merge.

This commit changes the `Discussions::ResolveService` to run the
auto-merge service if it is enabled.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/210068

app/services/discussions/resolve_service.rb

@@ -7,6 +7,7 @@ module Discussions
     def initialize(project, user = nil, params = {})
       @discussions = Array.wrap(params.fetch(:one_or_more_discussions))
       @follow_up_issue = params[:follow_up_issue]
+      @resolved_count = 0
 
       raise ArgumentError, 'Discussions must be all for the same noteable' \
         unless noteable_is_same?
@@ -16,6 +17,7 @@ module Discussions
 
     def execute
       discussions.each(&method(:resolve_discussion))
+      process_auto_merge
     end
 
     private
@@ -36,6 +38,7 @@ module Discussions
       return unless discussion.can_resolve?(current_user)
 
       discussion.resolve!(current_user)
+      @resolved_count += 1
 
       MergeRequests::ResolvedDiscussionNotificationService.new(project, current_user).execute(merge_request) if merge_request
       SystemNoteService.discussion_continued_in_issue(discussion, project, current_user, follow_up_issue) if follow_up_issue
@@ -50,5 +53,17 @@ module Discussions
         first_discussion.noteable if first_discussion.for_merge_request?
       end
     end
+
+    def process_auto_merge
+      return unless merge_request
+      return unless @resolved_count.positive?
+      return unless discussions_ready_to_merge?
+
+      AutoMergeProcessWorker.perform_async(merge_request.id)
+    end
+
+    def discussions_ready_to_merge?
+      merge_request.auto_merge_enabled? && merge_request.mergeable_discussions_state?
+    end
   end
 end

changelogs/unreleased/sh-fix-auto-merge-after-resolve-discussions.yml

+---
+title: Fix auto-merge not running after discussions resolved
+merge_request: 33371
+author:
+type: fixed

spec/services/discussions/resolve_service_spec.rb

@@ -6,7 +6,7 @@ describe Discussions::ResolveService do
   describe '#execute' do
     let_it_be(:project) { create(:project, :repository) }
     let_it_be(:user) { create(:user, developer_projects: [project]) }
-    let_it_be(:merge_request) { create(:merge_request, source_project: project) }
+    let_it_be(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds, source_project: project) }
     let(:discussion) { create(:diff_note_on_merge_request, noteable: merge_request, project: project).to_discussion }
     let(:service) { described_class.new(project, user, one_or_more_discussions: discussion) }
 
@@ -32,6 +32,36 @@ describe Discussions::ResolveService do
       service.execute
     end
 
+    it 'schedules an auto-merge' do
+      expect(AutoMergeProcessWorker).to receive(:perform_async).with(discussion.noteable.id)
+
+      service.execute
+    end
+
+    context 'with a project that requires all discussion to be resolved' do
+      before do
+        project.update(only_allow_merge_if_all_discussions_are_resolved: true)
+      end
+
+      after do
+        project.update(only_allow_merge_if_all_discussions_are_resolved: false)
+      end
+
+      let_it_be(:other_discussion) { create(:diff_note_on_merge_request, noteable: merge_request, project: project).to_discussion }
+
+      it 'does not schedule an auto-merge' do
+        expect(AutoMergeProcessWorker).not_to receive(:perform_async)
+
+        service.execute
+      end
+
+      it 'schedules an auto-merge' do
+        expect(AutoMergeProcessWorker).to receive(:perform_async)
+
+        described_class.new(project, user, one_or_more_discussions: [discussion, other_discussion]).execute
+      end
+    end
+
     it 'adds a system note to the discussion' do
       issue = create(:issue, project: project)
 
@@ -70,6 +100,12 @@ describe Discussions::ResolveService do
 
         service.execute
       end
+
+      it 'does not schedule an auto-merge' do
+        expect(AutoMergeProcessWorker).not_to receive(:perform_async)
+
+        service.execute
+      end
     end
   end
 end