Group milestone: fix members autocomplete to include users [RUN AS-IF-FOSS]

app/services/groups/participants_service.rb

@@ -23,9 +23,9 @@ module Groups
     end
 
     def group_members
-      return [] unless noteable
+      return [] unless group
 
-      @group_members ||= sorted(noteable.group.direct_and_indirect_users)
+      @group_members ||= sorted(group.direct_and_indirect_users)
     end
   end
 end

spec/features/groups/milestones/gfm_autocomplete_spec.rb

@@ -16,6 +16,7 @@ RSpec.describe 'GFM autocomplete', :js do
       fill_in 'Description', with: User.reference_prefix
       wait_for_requests
       expect(find_autocomplete_menu).to be_visible
+      expect_autocomplete_entry(user.name)
       expect_autocomplete_entry(group.name)
 
       fill_in 'Description', with: Label.reference_prefix

spec/services/groups/participants_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Groups::ParticipantsService do
+  describe '#group_members' do
+    let(:user) { create(:user) }
+    let(:parent_group) { create(:group) }
+    let(:group) { create(:group, parent: parent_group) }
+    let(:subgroup) { create(:group, parent: group) }
+    let(:subproject) { create(:project, group: subgroup) }
+
+    it 'returns all members in parent groups, sub-groups, and sub-projects' do
+      parent_group.add_developer(create(:user))
+      subgroup.add_developer(create(:user))
+      subproject.add_developer(create(:user))
+
+      result = described_class.new(group, user).execute(nil)
+
+      expected_users = (group.self_and_hierarchy.flat_map(&:users) + subproject.users)
+        .map { |user| user_to_autocompletable(user) }
+
+      expect(expected_users.count).to eq(3)
+      expect(result).to include(*expected_users)
+    end
+  end
+
+  def user_to_autocompletable(user)
+    {
+      type: user.class.name,
+      username: user.username,
+      name: user.name,
+      avatar_url: user.avatar_url,
+      availability: user&.status&.availability
+    }
+  end
+end