Check for 422 error when editing stage

ee/app/assets/javascripts/analytics/cycle_analytics/store/actions.js

@@ -259,9 +259,23 @@ export const receiveUpdateStageSuccess = ({ commit, dispatch }, updatedData) =>
   dispatch('setSelectedStage', updatedData);
 };
 
-export const receiveUpdateStageError = ({ commit }) => {
+export const receiveUpdateStageError = (
+  { commit },
+  { error: { response: { status = 400, data: errorData } = {} } = {}, data },
+) => {
   commit(types.RECEIVE_UPDATE_STAGE_RESPONSE);
-  createFlash(__('There was a problem saving your custom stage, please try again'));
+  const ERROR_NAME_RESERVED = 'is reserved';
+
+  let message = __('There was a problem saving your custom stage, please try again');
+  if (status && status === httpStatus.UNPROCESSABLE_ENTITY) {
+    const { errors } = errorData;
+    const { name } = data;
+    if (errors.name && errors.name[0] === ERROR_NAME_RESERVED) {
+      message = __(`'${name}' stage already exists`);
+    }
+  }
+
+  createFlash(__(message));
 };
 
 export const updateStage = ({ dispatch, state }, { id, ...rest }) => {
@@ -273,7 +287,7 @@ export const updateStage = ({ dispatch, state }, { id, ...rest }) => {
 
   return Api.cycleAnalyticsUpdateStage(id, fullPath, { ...rest })
     .then(({ data }) => dispatch('receiveUpdateStageSuccess', data))
-    .catch(error => dispatch('receiveUpdateStageError', error));
+    .catch(error => dispatch('receiveUpdateStageError', { error, data: { id, ...rest } }));
 };
 
 export const requestRemoveStage = ({ commit }) => commit(types.REQUEST_REMOVE_STAGE);

ee/spec/features/analytics/cycle_analytics/cycle_analytics_spec.rb

@@ -399,6 +399,14 @@ describe 'Group Cycle Analytics', :js do
 
             expect(page.find(stage_save_button)[:disabled]).to eq "true"
           end
+
+          it 'with a default name' do
+            name = 'issue'
+            fill_in name_field, with: name
+            page.find(stage_save_button).click
+
+            expect(page.find('.flash-alert')).to have_text("'#{name}' stage already exists")
+          end
         end
       end
 

ee/spec/frontend/analytics/cycle_analytics/store/actions_spec.js

@@ -562,25 +562,51 @@ describe('Cycle analytics actions', () => {
       });
 
       it('dispatches receiveUpdateStageError', done => {
+        const data = {
+          id: stageId,
+          ...payload,
+        };
         testAction(
           actions.updateStage,
-          {
-            id: stageId,
-            ...payload,
-          },
+          data,
           state,
           [],
           [
             { type: 'requestUpdateStage' },
             {
               type: 'receiveUpdateStageError',
-              payload: error,
+              payload: { error, data },
             },
           ],
           done,
         );
       });
 
+      it('flashes an error if the stage name already exists', done => {
+        actions.receiveUpdateStageError(
+          {
+            commit: () => {},
+            state,
+          },
+          {
+            error: {
+              response: {
+                status: 422,
+                data: {
+                  errors: { name: ['is reserved'] },
+                },
+              },
+            },
+            data: {
+              name: stageId,
+            },
+          },
+        );
+
+        shouldFlashAMessage(`'${stageId}' stage already exists`);
+        done();
+      });
+
       it('flashes an error message', done => {
         actions.receiveUpdateStageError(
           {