Add Additional Minimal Access API Response Error Messages

Current return message does not tell the caller why the call failed.

This change adds two additional messages to the returned error message.

Changelog: changed
EE: true
Co-authored-by: Abdul Wadood <awadood@gitlab.com>

ee/app/models/ee/group_member.rb

@@ -45,6 +45,11 @@ module EE
       return if access_level.in?(levels)
 
       errors.add(:access_level, "is not included in the list")
+
+      if access_level == ::Gitlab::Access::MINIMAL_ACCESS
+        errors.add(:access_level, "supported on top level groups only") if group.has_parent?
+        errors.add(:access_level, "not supported by license") unless group.feature_available?(:minimal_access_role)
+      end
     end
 
     override :post_create_hook

ee/spec/requests/api/members_spec.rb

@@ -7,11 +7,13 @@ RSpec.describe API::Members do
 
   context 'group members endpoints for group with minimal access feature' do
     let_it_be(:group) { create(:group) }
+    let_it_be(:subgroup) { create(:group, parent: group) }
     let_it_be(:minimal_access_member) { create(:group_member, :minimal_access, source: group) }
     let_it_be(:owner) { create(:user) }
 
     before do
       group.add_owner(owner)
+      subgroup.add_owner(owner)
     end
 
     describe "GET /groups/:id/members" do
@@ -41,21 +43,23 @@ RSpec.describe API::Members do
              params: { user_id: stranger.id, access_level: Member::MINIMAL_ACCESS }
       end
 
-      context 'when minimal access role is not available' do
+      context 'when minimal access license is not available' do
         it 'does not create a member' do
           expect do
             subject
           end.not_to change { group.all_group_members.count }
 
           expect(response).to have_gitlab_http_status(:bad_request)
-          expect(json_response['message']).to eq({ 'access_level' => ['is not included in the list'] })
+          expect(json_response['message']).to eq({ 'access_level' => ['is not included in the list', 'not supported by license'] })
         end
       end
 
-      context 'when minimal access role is available' do
-        it 'creates a member' do
+      context 'when minimal access license is available' do
+        before do
           stub_licensed_features(minimal_access_role: true)
+        end
 
+        it 'creates a member' do
           expect do
             subject
           end.to change { group.all_group_members.count }.by(1)
@@ -63,6 +67,16 @@ RSpec.describe API::Members do
           expect(response).to have_gitlab_http_status(:created)
           expect(json_response['id']).to eq(stranger.id)
         end
+
+        it 'cannot be assigned to subgroup' do
+          expect do
+            post api("/groups/#{subgroup.id}/members", owner),
+                 params: { user_id: stranger.id, access_level: Member::MINIMAL_ACCESS }
+          end.not_to change { subgroup.all_group_members.count }
+
+          expect(response).to have_gitlab_http_status(:bad_request)
+          expect(json_response['message']).to eq({ 'access_level' => ['is not included in the list', 'supported on top level groups only'] })
+        end
       end
     end