Multiple issue assignee: CE restriction for multiple assignees

app/services/issues/base_service.rb

@@ -24,6 +24,9 @@ module Issues
     def filter_assignee(issuable)
       return if params[:assignee_ids].blank?
+      # The number of assignees is limited by one for GitLab CE
+      params[:assignee_ids].slice!(0, 1)
+
       assignee_ids = params[:assignee_ids].select { |assignee_id| assignee_can_read?(issuable, assignee_id) }
       if params[:assignee_ids].map(&:to_s) == [IssuableFinder::NONE]

spec/requests/api/issues_spec.rb

@@ -772,6 +772,17 @@ describe API::Issues do
       end
     end
+    context 'CE restrictions' do
+      it 'creates a new project issue with no more than one assignee' do
+        post api("/projects/#{project.id}/issues", user),
+          title: 'new issue', assignee_ids: [user2.id, guest.id]
+
+        expect(response).to have_http_status(201)
+        expect(json_response['title']).to eq('new issue')
+        expect(json_response['assignees'].count).to eq(1)
+      end
+    end
+
     it 'creates a new project issue' do
       post api("/projects/#{project.id}/issues", user),
         title: 'new issue', labels: 'label, label2', weight: 3,
@@ -1111,6 +1122,17 @@ describe API::Issues do
       expect(json_response['assignees'].first['name']).to eq(user2.name)
     end
+
+    context 'CE restrictions' do
+      it 'updates an issue with several assignee but only one has been applied' do
+        put api("/projects/#{project.id}/issues/#{issue.iid}", user),
+          assignee_ids: [user2.id, guest.id]
+
+        expect(response).to have_http_status(200)
+
+        expect(json_response['assignees'].size).to eq(1)
+      end
+    end
   end
   describe 'PUT /projects/:id/issues/:issue_iid to update labels' do

spec/services/notes/slash_commands_service_spec.rb

@@ -220,4 +220,31 @@ describe Notes::SlashCommandsService, services: true do
       let(:note) { build(:note_on_commit, project: project) }
     end
   end
+
+  context 'CE restriction for issue assignees' do
+    describe '/assign' do
+      let(:project) { create(:empty_project) }
+      let(:master) { create(:user).tap { |u| project.team << [u, :master] } }
+      let(:assignee) { create(:user) }
+      let(:master) { create(:user) }
+      let(:service) { described_class.new(project, master) }
+      let(:note) { create(:note_on_issue, note: note_text, project: project) }
+
+      let(:note_text) do
+        %(/assign @#{assignee.username} @#{master.username}\n")
+      end
+
+      before do
+        project.team << [master, :master]
+        project.team << [assignee, :master]
+      end
+
+      it 'adds only one assignee from the list' do
+        content, command_params = service.extract_commands(note)
+        service.execute(command_params, note)
+
+        expect(note.noteable.assignees.count).to eq(1)
+      end
+    end
+  end
 end