Retrieve issues from subgroups when rendering group milestone

app/models/milestone.rb

@@ -341,6 +341,6 @@ class Milestone < ApplicationRecord
   end
 
   def issues_finder_params
-    { project_id: project_id, group_id: group_id }.compact
+    { project_id: project_id, group_id: group_id, include_subgroups: group_id.present? }.compact
   end
 end

changelogs/unreleased/36205-issues-in-group-milestones.yml

+---
+title: Retrieve issues from subgroups when rendering group milestone
+merge_request: 21024
+author:
+type: fixed

spec/models/concerns/milestoneish_spec.rb

@@ -192,6 +192,23 @@ describe Milestone, 'Milestoneish' do
         end
       end
     end
+
+    context 'when milestone is at parent level group' do
+      let(:parent_group) { create(:group) }
+      let(:group) { create(:group, parent: parent_group) }
+      let(:project) { create(:project, namespace: group) }
+      let(:milestone) { create(:milestone, group: parent_group) }
+
+      it 'does not return any merge request for a non member' do
+        merge_requests = milestone.merge_requests_visible_to_user(non_member)
+        expect(merge_requests).to be_empty
+      end
+
+      it 'returns milestone merge requests for a member' do
+        merge_requests = milestone.merge_requests_visible_to_user(member)
+        expect(merge_requests).to contain_exactly(merge_request)
+      end
+    end
   end
 
   describe '#complete?' do