Fix setting assignees on boards when relative URL is enabled

app/assets/javascripts/boards/index.js

+import { IntrospectionFragmentMatcher } from 'apollo-cache-inmemory';
 import Vue from 'vue';
 import VueApollo from 'vue-apollo';
 import { mapActions, mapGetters } from 'vuex';
@@ -35,13 +36,26 @@ import {
 } from '~/lib/utils/common_utils';
 import { __ } from '~/locale';
 import sidebarEventHub from '~/sidebar/event_hub';
+import introspectionQueryResultData from '~/sidebar/fragmentTypes.json';
 import boardConfigToggle from './config_toggle';
 import mountMultipleBoardsSwitcher from './mount_multiple_boards_switcher';
 
 Vue.use(VueApollo);
 
+const fragmentMatcher = new IntrospectionFragmentMatcher({
+  introspectionQueryResultData,
+});
+
 const apolloProvider = new VueApollo({
-  defaultClient: createDefaultClient(),
+  defaultClient: createDefaultClient(
+    {},
+    {
+      cacheConfig: {
+        fragmentMatcher,
+      },
+      assumeImmutableResults: true,
+    },
+  ),
 });
 
 let issueBoardsApp;

app/assets/javascripts/sidebar/components/assignees/sidebar_assignees_widget.vue

@@ -245,8 +245,8 @@ export default {
           @input="setDirtyState"
         >
           <template #footer>
-            <gl-dropdown-item>
-              <sidebar-invite-members v-if="directlyInviteMembers" />
+            <gl-dropdown-item v-if="directlyInviteMembers">
+              <sidebar-invite-members />
             </gl-dropdown-item> </template
         ></user-select>
       </template>

app/views/shared/boards/components/sidebar/_assignee.html.haml

 - dropdown_options = assignees_dropdown_options('issue')
+- relative_url = Gitlab.config.gitlab.relative_url_root || '/'
 
 .block.assignee{ ref: "assigneeBlock" }
   %template{ "v-if" => "issue.assignees" }
     %sidebar-assignees-widget{ ":iid" => "String(issue.iid)",
-      ":full-path" => "issue.path.split('/-/')[0].substring(1)",
+      ":full-path" => "issue.path.split('/-/')[0].substring(1).replace(`#{relative_url}`, '')",
       ":initial-assignees" => "issue.assignees",
       ":multiple-assignees" => "!Boolean(#{dropdown_options[:data][:"max-select"]})",
       "@assignees-updated" => "setAssignees" }

changelogs/unreleased/329624-cannot-set-assignee-in-boards-view-for-self-managed-gitlab-with-re.yml

+---
+title: Resolve Cannot Set Assignee in Boards View for self-managed GitLab with Relative
+  URL
+merge_request: 60711
+author:
+type: fixed