Load the Merge Request > Commits tab lazily

app/controllers/projects/merge_requests_controller.rb

@@ -71,7 +71,10 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   end
 
   def commits
-    render 'show'
+    respond_to do |format|
+      format.html { render 'show' }
+      format.json { render json: { html: view_to_html_string('projects/merge_requests/show/_commits') } }
+    end
   end
 
   def new

app/views/projects/merge_requests/_show.html.haml

@@ -56,7 +56,8 @@
     #notes.notes.tab-pane.voting_notes
       = render "projects/merge_requests/discussion"
     #commits.commits.tab-pane
-      = render "projects/merge_requests/show/commits"
+      - if current_page?(action: 'commits')
+        = render "projects/merge_requests/show/commits"
     #diffs.diffs.tab-pane
       - if current_page?(action: 'diffs')
         = render "projects/merge_requests/show/diffs"
@@ -64,7 +65,6 @@
   .mr-loading-status
     = spinner
 
-
 :javascript
   var merge_request;
 

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -79,23 +79,72 @@ describe Projects::MergeRequestsController do
     end
   end
 
-  context '#diffs with forked projects with submodules' do
-    render_views
-    let(:project) { create(:project) }
-    let(:fork_project) { create(:forked_project_with_submodules) }
-    let(:merge_request) { create(:merge_request_with_diffs, source_project: fork_project, source_branch: 'add-submodule-version-bump', target_branch: 'master', target_project: project) }
-
-    before do
-      fork_project.build_forked_project_link(forked_to_project_id: fork_project.id, forked_from_project_id: project.id)
-      fork_project.save
-      merge_request.reload
+  describe 'GET diffs' do
+    def go(format: 'html')
+      get :diffs, namespace_id: project.namespace.to_param,
+        project_id: project.to_param, id: merge_request.iid, format: format
     end
 
-    it '#diffs' do
-      get(:diffs, namespace_id: project.namespace.to_param,
-          project_id: project.to_param, id: merge_request.iid, format: 'json')
-      expect(response).to be_success
-      expect(response.body).to have_content('Subproject commit')
+    context 'as html' do
+      it 'renders the diff template' do
+        go
+
+        expect(response).to render_template('diffs')
+      end
+    end
+
+    context 'as json' do
+      it 'renders the diffs template to a string' do
+        go format: 'json'
+
+        expect(response).to render_template('projects/merge_requests/show/_diffs')
+        expect(JSON.parse(response.body)).to have_key('html')
+      end
+    end
+
+    context 'with forked projects with submodules' do
+      render_views
+
+      let(:project) { create(:project) }
+      let(:fork_project) { create(:forked_project_with_submodules) }
+      let(:merge_request) { create(:merge_request_with_diffs, source_project: fork_project, source_branch: 'add-submodule-version-bump', target_branch: 'master', target_project: project) }
+
+      before do
+        fork_project.build_forked_project_link(forked_to_project_id: fork_project.id, forked_from_project_id: project.id)
+        fork_project.save
+        merge_request.reload
+      end
+
+      it 'renders' do
+        go format: 'json'
+
+        expect(response).to be_success
+        expect(response.body).to have_content('Subproject commit')
+      end
+    end
+  end
+
+  describe 'GET commits' do
+    def go(format: 'html')
+      get :commits, namespace_id: project.namespace.to_param,
+        project_id: project.to_param, id: merge_request.iid, format: format
+    end
+
+    context 'as html' do
+      it 'renders the show template' do
+        go
+
+        expect(response).to render_template('show')
+      end
+    end
+
+    context 'as json' do
+      it 'renders the commits template to a string' do
+        go format: 'json'
+
+        expect(response).to render_template('projects/merge_requests/show/_commits')
+        expect(JSON.parse(response.body)).to have_key('html')
+      end
     end
   end
 end