Allow a member to have an access level equal to parent group

Suppose you have this configuration:

1. Subgroup `hello/world`
2. Subgroup `hello/mergers`.
3. Project `hello/world/my-project` has invited group `hello/world` to
access protected branches.
4. The rule allows the group to merge but no one can push.
5. User `newuser` has Owner access to the parent group `hello`.

Previously, there was no way for the user `newuser` to be added to the
`hello/mergers` group since the validation only allowed a user to be
added at a higher access level.

Since membership in a subgroup confers certain access rights, such as
being able to merge or push code to protected branches, we have to
loosen the validation and allow someone to be added at an equal level
granted by the parent group.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/11323

app/models/member.rb

@@ -446,10 +446,10 @@ class Member < ApplicationRecord
   end
 
   def higher_access_level_than_group
-    if highest_group_member && highest_group_member.access_level >= access_level
+    if highest_group_member && highest_group_member.access_level > access_level
       error_parameters = { access: highest_group_member.human_access, group_name: highest_group_member.group.name }
 
-      errors.add(:access_level, s_("should be higher than %{access} inherited membership from group %{group_name}") % error_parameters)
+      errors.add(:access_level, s_("should be greater than or equal to %{access} inherited membership from group %{group_name}") % error_parameters)
     end
   end
 end

changelogs/unreleased/sh-allow-equal-level-in-subgroup-membership.yml

+---
+title: Allow a member to have an access level equal to parent group
+merge_request: 27913
+author:
+type: fixed

locale/gitlab.pot

@@ -11385,7 +11385,7 @@ msgstr[1] ""
 msgid "score"
 msgstr ""
 
-msgid "should be higher than %{access} inherited membership from group %{group_name}"
+msgid "should be greater than or equal to %{access} inherited membership from group %{group_name}"
 msgstr ""
 
 msgid "show less"

spec/models/member_spec.rb

@@ -70,6 +70,16 @@ describe Member do
         expect(child_member).not_to be_valid
       end
 
+      # Membership in a subgroup confers certain access rights, such as being
+      # able to merge or push code to protected branches.
+      it "is valid with an equal level" do
+        child_member.access_level = GroupMember::DEVELOPER
+
+        child_member.validate
+
+        expect(child_member).to be_valid
+      end
+
       it "is valid with a higher level" do
         child_member.access_level = GroupMember::MAINTAINER
 

spec/requests/api/members_spec.rb

@@ -236,7 +236,7 @@ describe API::Members do
                params: { user_id: stranger.id, access_level: Member::REPORTER }
 
           expect(response).to have_gitlab_http_status(400)
-          expect(json_response['message']['access_level']).to eq(["should be higher than Developer inherited membership from group #{parent.name}"])
+          expect(json_response['message']['access_level']).to eq(["should be greater than or equal to Developer inherited membership from group #{parent.name}"])
         end
 
         it 'creates the member if group level is lower', :nested_groups do

spec/support/shared_examples/models/member_shared_examples.rb

@@ -41,7 +41,7 @@ shared_examples_for 'inherited access level as a member of entity' do
 
       member.update(access_level: Gitlab::Access::REPORTER)
 
-      expect(member.errors.full_messages).to eq(["Access level should be higher than Developer inherited membership from group #{parent_entity.name}"])
+      expect(member.errors.full_messages).to eq(["Access level should be greater than or equal to Developer inherited membership from group #{parent_entity.name}"])
     end
 
     it 'allows changing the level from a non existing member' do