Make smarter suggestion for assign commands

Uses Issuable assignees info to filter list of users suggested
in slash commands for assignees.

app/assets/javascripts/gfm_auto_complete.js

 import $ from 'jquery';
 import 'at.js';
 import _ from 'underscore';
+import SidebarMediator from '~/sidebar/sidebar_mediator';
 import glRegexp from './lib/utils/regexp';
 import AjaxCache from './lib/utils/ajax_cache';
 import { spriteIcon } from './lib/utils/common_utils';
@@ -53,8 +54,8 @@ export const defaultAutocompleteConfig = {
 };
 
 class GfmAutoComplete {
-  constructor(dataSources) {
-    this.dataSources = dataSources || {};
+  constructor(dataSources = {}) {
+    this.dataSources = dataSources;
     this.cachedData = {};
     this.isLoadingData = {};
   }
@@ -199,6 +200,16 @@ class GfmAutoComplete {
   }
 
   setupMembers($input) {
+    const fetchData = this.fetchData.bind(this);
+    const MEMBER_COMMAND = {
+      ASSIGN: '/assign',
+      UNASSIGN: '/unassign',
+      REASSIGN: '/reassign',
+      CC: '/cc',
+    };
+    let assignees = [];
+    let command = '';
+
     // Team Members
     $input.atwho({
       at: '@',
@@ -225,6 +236,48 @@ class GfmAutoComplete {
       callbacks: {
         ...this.getDefaultCallbacks(),
         beforeSave: membersBeforeSave,
+        matcher(flag, subtext) {
+          const subtextNodes = subtext
+            .split(/\n+/g)
+            .pop()
+            .split(GfmAutoComplete.regexSubtext);
+
+          // Check if @ is followed by '/assign', '/reassign', '/unassign' or '/cc' commands.
+          command = subtextNodes.find(node => {
+            if (Object.values(MEMBER_COMMAND).includes(node)) {
+              return node;
+            }
+            return null;
+          });
+
+          // Cache assignees list for easier filtering later
+          assignees = SidebarMediator.singleton?.store?.assignees?.map(
+            assignee => `${assignee.username} ${assignee.name}`,
+          );
+
+          const match = GfmAutoComplete.defaultMatcher(flag, subtext, this.app.controllers);
+          return match && match.length ? match[1] : null;
+        },
+        filter(query, data, searchKey) {
+          if (GfmAutoComplete.isLoading(data)) {
+            fetchData(this.$inputor, this.at);
+            return data;
+          }
+
+          if (data === GfmAutoComplete.defaultLoadingData) {
+            return $.fn.atwho.default.callbacks.filter(query, data, searchKey);
+          }
+
+          if (command === MEMBER_COMMAND.ASSIGN) {
+            // Only include members which are not assigned to Issuable currently
+            return data.filter(member => !assignees.includes(member.search));
+          } else if (command === MEMBER_COMMAND.UNASSIGN) {
+            // Only include members which are assigned to Issuable currently
+            return data.filter(member => assignees.includes(member.search));
+          }
+
+          return data;
+        },
       },
     });
   }

changelogs/unreleased/199698-smart-member-suggestions.yml

+---
+title: Make smarter user suggestions for assign slash commands
+merge_request: 24294
+author:
+type: added

ee/spec/features/issues/gfm_autocomplete_ee_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'GFM autocomplete EE', :js do
+  let(:user) { create(:user, name: '💃speciąl someone💃', username: 'someone.special') }
+  let(:another_user) { create(:user, name: 'another user', username: 'another.user') }
+  let(:project) { create(:project) }
+  let(:issue) { create(:issue, project: project) }
+
+  before do
+    project.add_maintainer(user)
+  end
+
+  context 'assignees' do
+    let(:issue_assignee) { create(:issue, project: project) }
+
+    before do
+      issue_assignee.update(assignees: [user])
+
+      sign_in(user)
+      visit project_issue_path(project, issue_assignee)
+
+      wait_for_requests
+    end
+
+    it 'only lists users who are currently assigned to the issue when using /unassign' do
+      note = find('#note-body')
+      page.within '.timeline-content-form' do
+        note.native.send_keys('/una')
+      end
+
+      find('.atwho-view li', text: '/unassign')
+      note.native.send_keys(:tab)
+
+      wait_for_requests
+
+      users = find('#at-view-users .atwho-view-ul')
+      expect(users).to have_content(user.username)
+      expect(users).not_to have_content(another_user.username)
+    end
+  end
+end

spec/features/issues/gfm_autocomplete_spec.rb

@@ -282,6 +282,32 @@ describe 'GFM autocomplete', :js do
     end
   end
 
+  context 'assignees' do
+    let(:issue_assignee) { create(:issue, project: project) }
+
+    before do
+      issue_assignee.update(assignees: [user])
+
+      visit project_issue_path(project, issue_assignee)
+
+      wait_for_requests
+    end
+
+    it 'lists users who are currently not assigned to the issue when using /assign' do
+      note = find('#note-body')
+      page.within '.timeline-content-form' do
+        note.native.send_keys('/as')
+      end
+
+      find('.atwho-view li', text: '/assign')
+      note.native.send_keys(:tab)
+
+      wait_for_requests
+
+      expect(find('#at-view-users .atwho-view-ul')).not_to have_content(user.username)
+    end
+  end
+
   context 'labels' do
     it 'opens autocomplete menu for Labels when field starts with text with item escaping HTML characters' do
       create(:label, project: project, title: label_xss_title)