Fix assignees search to show only project members

app/assets/javascripts/boards/graphql/users_search.query.graphql

-query usersSearch($search: String!) {
-  users(search: $search) {
-    nodes {
-      username
-      name
-      webUrl
-      avatarUrl
-      id
-    }
-  }
-}

app/assets/javascripts/graphql_shared/queries/users_search.query.graphql

 #import "../fragments/user.fragment.graphql"
 
-query usersSearch($search: String!) {
-  users(search: $search) {
+query usersSearch($search: String!, $fullPath: ID!) {
+  issuable: project(fullPath: $fullPath) {
+    users: projectMembers(search: $search) {
       nodes {
+        user {
           ...User
         }
       }
+    }
+  }
 }

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

@@ -104,11 +104,22 @@ export default {
       query: searchUsers,
       variables() {
         return {
+          fullPath: this.fullPath,
           search: this.search,
         };
       },
       update(data) {
-        return data.users?.nodes || [];
+        const searchResults = data.issuable?.users?.nodes.map(({ user }) => user) || [];
+        const mergedSearchResults = this.participants.reduce((acc, current) => {
+          if (
+            !acc.some((user) => current.username === user.username) &&
+            (current.name.includes(this.search) || current.username.includes(this.search))
+          ) {
+            acc.push(current);
+          }
+          return acc;
+        }, searchResults);
+        return mergedSearchResults;
       },
       debounce: 250,
       skip() {
@@ -185,7 +196,7 @@ export default {
       return this.selected.some(isCurrentUser) || this.participants.some(isCurrentUser);
     },
     noUsersFound() {
-      return !this.isSearchEmpty && this.unselectedFiltered.length === 0;
+      return !this.isSearchEmpty && this.searchUsers.length === 0;
     },
     showCurrentUser() {
       return !this.isCurrentUserInParticipants && (this.isSearchEmpty || this.isSearching);

changelogs/unreleased/322960-degredation-in-assigning-team-members-on-boards-view.yml

+---
+title: Fix assignees search to show only project members
+merge_request: 55396
+author:
+type: fixed

ee/spec/frontend/sidebar/mock_data.js

@@ -130,25 +130,31 @@ export const issuableQueryResponse = {
 
 export const searchQueryResponse = {
   data: {
+    issuable: {
       users: {
         nodes: [
           {
+            user: {
               id: '1',
               avatarUrl: '/avatar',
               name: 'root',
               username: 'root',
               webUrl: 'root',
             },
+          },
           {
+            user: {
               id: '3',
               avatarUrl: '/avatar',
               name: 'rookie',
               username: 'rookie',
               webUrl: 'rookie',
             },
+          },
         ],
       },
     },
+  },
 };
 
 export const updateIssueAssigneesMutationResponse = {