Automatic merge of gitlab-org/gitlab-ce master

app/services/merge_requests/base_service.rb

@@ -63,6 +63,7 @@ module MergeRequests
       # 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?
 
       Ci::CreatePipelineService
         .new(merge_request.source_project, user, ref: merge_request.source_branch)

changelogs/unreleased/not-run-pipeline-on-empty-merge-request.yml

+---
+title: Don't create new merge request pipeline without commits
+merge_request: 24503
+author: Hiroyuki Sato
+type: added

spec/services/merge_requests/create_service_spec.rb

@@ -197,6 +197,24 @@ describe MergeRequests::CreateService do
             expect(merge_request.actual_head_pipeline).to be_merge_request
           end
 
+          context 'when there are no commits between source branch and target branch' do
+            let(:opts) do
+              {
+                title: 'Awesome merge_request',
+                description: 'please fix',
+                source_branch: 'not-merged-branch',
+                target_branch: 'master'
+              }
+            end
+
+            it 'does not create a 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
+
           context "when branch pipeline was created before a merge request pipline has been created" do
             before do
               create(:ci_pipeline, project: merge_request.source_project,

spec/services/merge_requests/refresh_service_spec.rb

@@ -156,11 +156,15 @@ describe MergeRequests::RefreshService do
           }
         end
 
-        it 'create merge request pipeline' do
+        it 'create merge request pipeline with commits' do
           expect { subject }
             .to change { @merge_request.merge_request_pipelines.count }.by(1)
             .and change { @fork_merge_request.merge_request_pipelines.count }.by(1)
-            .and change { @another_merge_request.merge_request_pipelines.count }.by(1)
+            .and change { @another_merge_request.merge_request_pipelines.count }.by(0)
+
+          expect(@merge_request.has_commits?).to be_truthy
+          expect(@fork_merge_request.has_commits?).to be_truthy
+          expect(@another_merge_request.has_commits?).to be_falsy
         end
 
         context "when branch pipeline was created before a merge request pipline has been created" do