Add flash error for setAssignees failure

When set assignees fail in group issues board,
we show the createFlash banner

app/assets/javascripts/boards/components/board_assignee_dropdown.vue

@@ -134,7 +134,7 @@ export default {
 <template>
   <board-editable-item :loading="isSettingAssignees" :title="assigneeText" @close="saveAssignees">
     <template #collapsed>
-      <issuable-assignees :users="selected" @assign-self="assignSelf" />
+      <issuable-assignees :users="activeIssue.assignees" @assign-self="assignSelf" />
     </template>
 
     <template #default>

app/assets/javascripts/boards/stores/actions.js

@@ -13,7 +13,8 @@ import {
   formatIssue,
 } from '../boards_util';
 import boardStore from '~/boards/stores/boards_store';
-
+import createFlash from '~/flash';
+import { __ } from '~/locale';
 import updateAssigneesMutation from '~/vue_shared/components/sidebar/queries/updateAssignees.mutation.graphql';
 import listsIssuesQuery from '../graphql/lists_issues.query.graphql';
 import boardLabelsQuery from '../graphql/board_labels.query.graphql';
@@ -340,6 +341,9 @@ export default {
 
         return nodes;
       })
+      .catch(() => {
+        createFlash({ message: __('An error occurred while updating assignees.') });
+      })
       .finally(() => {
         commit(types.SET_ASSIGNEE_LOADING, false);
       });

changelogs/unreleased/ss-add-error-state-for-assignees.yml

+---
+title: Add flash message for setAssignees on group issue boards
+merge_request: 48277
+author:
+type: added

locale/gitlab.pot

@@ -3297,6 +3297,9 @@ msgstr ""
 msgid "An error occurred while updating approvers"
 msgstr ""
 
+msgid "An error occurred while updating assignees."
+msgstr ""
+
 msgid "An error occurred while updating configuration."
 msgstr ""
 

spec/frontend/boards/stores/actions_spec.js

@@ -18,6 +18,9 @@ import issueMoveListMutation from '~/boards/graphql/issue_move_list.mutation.gra
 import destroyBoardListMutation from '~/boards/graphql/board_list_destroy.mutation.graphql';
 import updateAssignees from '~/vue_shared/components/sidebar/queries/updateAssignees.mutation.graphql';
 import { fullBoardId, formatListIssues, formatBoardLists } from '~/boards/boards_util';
+import createFlash from '~/flash';
+
+jest.mock('~/flash');
 
 const expectNotImplemented = action => {
   it('is not implemented', () => {
@@ -666,6 +669,7 @@ describe('setAssignees', () => {
   const refPath = `${projectPath}#3`;
   const iid = '1';
 
+  describe('when succeeds', () => {
     beforeEach(() => {
       jest.spyOn(gqlClient, 'mutate').mockResolvedValue({
         data: { issueSetAssignees: { issue: { assignees: { nodes: [{ ...node }] } } } },
@@ -690,23 +694,35 @@ describe('setAssignees', () => {
         {},
         { activeIssue: { iid, referencePath: refPath }, commit: () => {} },
         [
-        {
-          type: 'SET_ASSIGNEE_LOADING',
-          payload: true,
-        },
+          { type: types.SET_ASSIGNEE_LOADING, payload: true },
           {
             type: 'UPDATE_ISSUE_BY_ID',
             payload: { prop: 'assignees', issueId: undefined, value: [node] },
           },
-        {
-          type: 'SET_ASSIGNEE_LOADING',
-          payload: false,
-        },
+          { type: types.SET_ASSIGNEE_LOADING, payload: false },
         ],
         [],
         done,
       );
     });
+  });
+
+  describe('when fails', () => {
+    beforeEach(() => {
+      jest.spyOn(gqlClient, 'mutate').mockRejectedValue();
+    });
+
+    it('calls createFlash', async () => {
+      await actions.setAssignees({
+        commit: () => {},
+        getters: { activeIssue: { iid, referencePath: refPath } },
+      });
+
+      expect(createFlash).toHaveBeenCalledWith({
+        message: 'An error occurred while updating assignees.',
+      });
+    });
+  });
 });
 
 describe('createNewIssue', () => {