Use merge request MERGE ref for attached merge request pipelines

Merge request pipelines are for prevalidating merge pipelines before
an actual merge.

app/services/merge_requests/base_service.rb

@@ -55,15 +55,7 @@ module MergeRequests
     end
 
     def create_pipeline_for(merge_request, user)
-      return unless Feature.enabled?(:ci_merge_request_pipeline,
-                                     merge_request.source_project,
-                                     default_enabled: true)
-
-      ##
-      # UpdateMergeRequestsWorker could be retried by an exception.
-      # MR pipelines should not be recreated in such case.
-      return if merge_request.merge_request_pipeline_exists?
-      return if merge_request.has_no_commits?
+      return unless can_create_pipeline_for?(merge_request)
 
       create_detached_merge_request_pipeline(merge_request, user)
     end
@@ -80,6 +72,16 @@ module MergeRequests
       end
     end
 
+    def can_create_pipeline_for?(merge_request)
+      ##
+      # UpdateMergeRequestsWorker could be retried by an exception.
+      # pipelines for merge request should not be recreated in such case.
+      return false if merge_request.merge_request_pipeline_exists?
+      return false if merge_request.has_no_commits?
+
+      true
+    end
+
     def can_use_merge_request_ref?(merge_request)
       Feature.enabled?(:ci_use_merge_request_ref, project, default_enabled: true) &&
         !merge_request.for_fork?

ee/app/services/ee/merge_requests/base_service.rb

@@ -3,6 +3,8 @@
 module EE
   module MergeRequests
     module BaseService
+      extend ::Gitlab::Utils::Override
+
       private
 
       def filter_params(merge_request)
@@ -16,6 +18,34 @@ module EE
 
         super
       end
+
+      override :create_pipeline_for
+      def create_pipeline_for(merge_request, user)
+        create_merge_request_pipeline_for(merge_request, user) || super
+      end
+
+      def create_merge_request_pipeline_for(merge_request, user)
+        return unless can_create_merge_request_pipeline_for?(merge_request)
+
+        ret = ::MergeRequests::MergeToRefService.new(merge_request.project, user)
+                                                .execute(merge_request)
+
+        if ret[:status] == :success
+          ::Ci::CreatePipelineService.new(merge_request.source_project, user,
+                                          ref: merge_request.merge_ref_path,
+                                          checkout_sha: ret[:commit_id],
+                                          target_sha: ret[:target_id],
+                                          source_sha: ret[:source_id])
+            .execute(:merge_request_event, merge_request: merge_request)
+        end
+      end
+
+      def can_create_merge_request_pipeline_for?(merge_request)
+        return false unless merge_request.project.merge_pipelines_enabled?
+        return false unless can_use_merge_request_ref?(merge_request)
+
+        can_create_pipeline_for?(merge_request)
+      end
     end
   end
 end

ee/changelogs/unreleased/create-merge-pipelines.yml

+---
+title: Use merge request MERGE ref for attached merge request pipelines
+merge_request: 9622
+author:
+type: added

ee/spec/services/ee/merge_requests/base_service_spec.rb

@@ -3,6 +3,8 @@
 require 'spec_helper'
 
 describe MergeRequests::BaseService do
+  include ProjectForksHelper
+
   subject { MergeRequests::CreateService.new(project, project.owner, params) }
 
   let(:project) { create(:project, :repository) }
@@ -34,4 +36,114 @@ describe MergeRequests::BaseService do
       end
     end
   end
+
+  describe '#create_pipeline_for' do
+    subject { service.execute }
+
+    let(:service) { MergeRequests::CreateService.new(source_project, user, opts) }
+    let(:user) { create(:user) }
+    let(:title) { 'Awesome merge request' }
+    let(:merge_pipelines_enabled) { true }
+    let(:merge_pipelines_license) { true }
+    let(:source_project) { project }
+    let(:source_branch) { 'feature' }
+    let(:target_project) { project }
+    let(:target_branch) { 'master' }
+
+    let(:opts) do
+      {
+        title: title,
+        description: 'A new fix',
+        source_branch: source_branch,
+        source_project: source_project,
+        target_branch: target_branch,
+        target_project: target_project
+      }
+    end
+
+    let(:ci_yaml) do
+      {
+        test: {
+          stage: 'test',
+          script: 'echo',
+          only: ['merge_requests']
+        }
+      }
+    end
+
+    before do
+      source_project.add_developer(user)
+      target_project.add_developer(user)
+      source_project.merge_pipelines_enabled = merge_pipelines_enabled
+      stub_licensed_features(merge_pipelines: merge_pipelines_license)
+      stub_ci_pipeline_yaml_file(YAML.dump(ci_yaml))
+    end
+
+    shared_examples_for 'creates a merge requst pipeline' do
+      it do
+        expect(subject).to be_persisted
+        expect(subject.all_pipelines.count).to eq(1)
+        expect(subject.all_pipelines.last).to be_merge_request_pipeline
+        expect(subject.all_pipelines.last).not_to be_detached_merge_request_pipeline
+      end
+    end
+
+    shared_examples_for 'creates a detached merge requst pipeline' do
+      it do
+        expect(subject).to be_persisted
+        expect(subject.all_pipelines.count).to eq(1)
+        expect(subject.all_pipelines.last).not_to be_merge_request_pipeline
+        expect(subject.all_pipelines.last).to be_detached_merge_request_pipeline
+      end
+    end
+
+    it_behaves_like 'creates a merge requst pipeline'
+
+    context 'when merge request is WIP' do
+      let(:title) { 'WIP: Awesome merge request' }
+
+      it_behaves_like 'creates a detached merge requst pipeline'
+    end
+
+    context 'when project setting for merge request pipelines is disabled' do
+      let(:merge_pipelines_enabled) { false }
+
+      it_behaves_like 'creates a detached merge requst pipeline'
+    end
+
+    context 'when ci_use_merge_request_ref feature flag is disabled' do
+      before do
+        stub_feature_flags(ci_use_merge_request_ref: false)
+      end
+
+      it_behaves_like 'creates a detached merge requst pipeline'
+    end
+
+    context 'when merge request is submitted from fork' do
+      let(:source_project) { fork_project(project, nil, repository: true) }
+
+      it_behaves_like 'creates a detached merge requst pipeline'
+    end
+
+    context 'when the CreateService is retried' do
+      it 'does not create a merge request pipeline twice' do
+        expect do
+          2.times { MergeRequests::CreateService.new(source_project, user, opts).execute }
+        end.to change { Ci::Pipeline.count }.by(1)
+      end
+    end
+
+    context 'when merge request has no commit' do
+      let(:source_branch) { 'empty-branch' }
+
+      it_behaves_like 'creates a detached merge requst pipeline'
+    end
+
+    context 'when merge request has a conflict' do
+      let(:source_branch) { 'feature' }
+      let(:target_branch) { 'feature_conflict' }
+
+      it_behaves_like 'creates a detached merge requst pipeline'
+    end
+  end
 end

spec/services/merge_requests/create_service_spec.rb

@@ -263,19 +263,6 @@ describe MergeRequests::CreateService do
               expect(merge_request.actual_head_pipeline).to be_merge_request_event
             end
           end
-
-          context "when the 'ci_merge_request_pipeline' feature flag is disabled" do
-            before do
-              stub_feature_flags(ci_merge_request_pipeline: false)
-            end
-
-            it 'does not create a detached merge request pipeline' do
-              expect(merge_request).to be_persisted
-
-              merge_request.reload
-              expect(merge_request.merge_request_pipelines.count).to eq(0)
-            end
-          end
         end
 
         context "when .gitlab-ci.yml does not have merge_requests keywords" do

spec/services/merge_requests/refresh_service_spec.rb

@@ -236,17 +236,6 @@ describe MergeRequests::RefreshService do
             end.not_to change { @merge_request.merge_request_pipelines.count }
           end
         end
-
-        context "when the 'ci_merge_request_pipeline' feature flag is disabled" do
-          before do
-            stub_feature_flags(ci_merge_request_pipeline: false)
-          end
-
-          it 'does not create a detached merge request pipeline' do
-            expect { subject }
-              .not_to change { @merge_request.merge_request_pipelines.count }
-          end
-        end
       end
 
       context "when .gitlab-ci.yml does not have merge_requests keywords" do