Add project group and ancestors to group list

This addresses an issue that arises when the owner of a path is the
group under which the project lives (such as `@gitlab-org` for the
Gitlab project..) Gitlab::CodeOwners::GroupsLoader did not add that
group to the list of groups when attempting to determine ownership. This
list of groups is expanded into a list of users that the user
attempting the action (typically a merge) is compared to. Sinc the
project's group is not added to the group list, its members are not
expanded and are thus missing from the list of owners for a given path.

Additionally, this will look not simply at the immediate group of the
project, but at the entire group tree ancestors to the root group. For
example, if the "merge_service" project is at

gitlab-org/engineering/source_code/merge_service

..then any of these groups would be considerable available for listing
as a code owner without having to be invited to the project:

@gitlab-org
@gitlab-org/engineering
@gitlab-org/engineering/source_code

This address both the proximate cause of
https://gitlab.com/gitlab-org/gitlab/-/issues/216345 but of the
long-requested feature https://gitlab.com/gitlab-org/gitlab/-/issues/32432

changelogs/unreleased/216345-extend-project-group-membership-checks-to-group-ancestors.yml

+---
+title: Consider project group and group ancestors when processing CODEOWNERS entries
+merge_request: 31152
+author:
+type: added

ee/lib/gitlab/code_owners/groups_loader.rb

@@ -23,7 +23,29 @@ module Gitlab
         return Group.none if extractor.names.empty?
 
         groups = project.invited_groups.where_full_path_in(extractor.names)
-        groups.with_route.with_users
+
+        if Feature.enabled?(:codeowners_match_ancestor_groups, default_enabled: true)
+          group_list = groups.with_route.with_users.to_a
+
+          if project.group
+            # If the project.group's ancestor group(s) are listed as owners, add
+            #   them to group_list
+            #
+            if applicable_ancestors(extractor.names).any?
+              group_list.concat(applicable_ancestors(extractor.names))
+            end
+          end
+
+          group_list.uniq
+        else
+          groups.with_route.with_users
+        end
+      end
+
+      def applicable_ancestors(extractor_names)
+        ancestor_groups = project.group.self_and_ancestors.with_route.with_users
+
+        ancestor_groups.select { |group| extractor_names.include?(group.full_path) }
       end
     end
   end

ee/spec/lib/gitlab/checks/diff_check_spec.rb

@@ -103,6 +103,71 @@ describe Gitlab::Checks::DiffCheck do
             expect(validation_result).to be_nil
           end
         end
+
+        context "when the codeowner entity is a group" do
+          let(:group) { create(:group) }
+          let(:project) { create(:project, :repository, namespace: group) }
+          let(:codeowner_content) do
+            <<~CODEOWNERS
+            *.rb @#{code_owner.username}
+            docs/CODEOWNERS @#{group.full_path}
+            *.js.coffee @#{group.full_path}
+            CODEOWNERS
+          end
+
+          before do
+            stub_feature_flags(sectional_codeowners: false)
+          end
+
+          shared_examples_for "returns nil" do
+            it "returns nil" do
+              expect(validation_result).to be_nil
+            end
+          end
+
+          shared_examples_for "returns codeowners validation message" do
+            it "returns an error message" do
+              expect(validation_result).to include("Pushes to protected branches")
+            end
+          end
+
+          context "and the project is under a subgroup" do
+            let(:subgroup) { create(:group, parent: group) }
+            let(:project) { create(:project, :repository, namespace: subgroup) }
+
+            context "and the user is part of the codeowning-group" do
+              before do
+                group.add_developer(user)
+              end
+
+              it_behaves_like "returns nil"
+            end
+
+            context "and the user is not part of the codeowning-group" do
+              it_behaves_like "returns codeowners validation message"
+            end
+
+            context "with :codeowners_match_ancestor_groups disabled" do
+              before do
+                stub_feature_flags(codeowners_match_ancestor_groups: false)
+              end
+
+              it_behaves_like "returns codeowners validation message"
+            end
+          end
+
+          context "and the user is part of the codeowning-group" do
+            before do
+              group.add_developer(user)
+            end
+
+            it_behaves_like "returns nil"
+          end
+
+          context "and the user is not part of the codeowning-group" do
+            it_behaves_like "returns codeowners validation message"
+          end
+        end
       end
 
       context "the MR doesn't contain a matching file path" do

ee/spec/lib/gitlab/code_owners/groups_loader_spec.rb

@@ -58,6 +58,18 @@ describe Gitlab::CodeOwners::GroupsLoader do
       end
     end
 
+    context "input matches project.group" do
+      let(:group) { create(:group) }
+      let(:project) { create(:project, :repository, namespace: group) }
+      let(:text) { "@#{project.group.full_path}" }
+
+      it "returns the project's group" do
+        load_groups
+
+        expect(entry).to have_received(:add_matching_groups_from).with([group])
+      end
+    end
+
     context 'input as array of strings' do
       let(:text) { super().lines }
 

ee/spec/lib/gitlab/code_owners/loader_spec.rb

@@ -71,7 +71,7 @@ describe Gitlab::CodeOwners::Loader do
         expect(loader.entries).to contain_exactly(expected_entry, other_entry)
       end
 
-      it 'only performs 3 query for users and groups' do
+      it 'performs 6 query for users and groups' do
         test_group = create(:group, path: 'test-group')
         test_group.add_developer(create(:user))
 
@@ -80,9 +80,12 @@ describe Gitlab::CodeOwners::Loader do
 
         project.invited_groups << [test_group, another_group]
 
-        # One query for users, one for the emails to later divide them across the entries
-        # one for groups with joined routes and users
-        expect { loader.entries }.not_to exceed_query_limit(3)
+        # - 1 query for users
+        # - 1 for the emails to later divide them across the entries
+        # - 2 for groups with joined routes and users
+        # - 2 for loading the users for the parent group(s)
+        #
+        expect { loader.entries }.not_to exceed_query_limit(6)
       end
     end