Bring back Rugged implementation of CommitIsAncestor

This brings back some of the changes in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20095.

For users using Gitaly on top of NFS, accessing the Git data directly
via Rugged is more performant than Gitaly. This merge request introduces
the feature flag `rugged_commit_is_ancestor` to activate the Rugged
path.

Part of four Rugged changes identified in
https://gitlab.com/gitlab-org/gitlab-ce/issues/57317.

1 files changed, 15 insertions, 1 deletions

diff --git a/spec/models/repository_spec.rb b/spec/models/repository_spec.rb
index 17201d8b90a..70630467d24 100644
--- a/spec/models/repository_spec.rb
+++ b/spec/models/repository_spec.rb
@@ -2237,7 +2237,7 @@ describe Repository do
     rugged.references.create("refs/remotes/#{remote_name}/#{branch_name}", target.id)
   end
 
-  describe '#ancestor?' do
+  shared_examples '#ancestor?' do
     let(:commit) { repository.commit }
     let(:ancestor) { commit.parents.first }
 
@@ -2261,6 +2261,20 @@ describe Repository do
     end
   end
 
+  describe '#ancestor? with Gitaly enabled' do
+    it_behaves_like "#ancestor?"
+  end
+
+  describe '#ancestor? with Rugged enabled', :enable_rugged do
+    it 'calls out to the Rugged implementation' do
+      allow_any_instance_of(Rugged).to receive(:merge_base).with(repository.commit.id, Gitlab::Git::BLANK_SHA).and_call_original
+
+      repository.ancestor?(repository.commit.id, Gitlab::Git::BLANK_SHA)
+    end
+
+    it_behaves_like '#ancestor?'
+  end
+
   describe '#archive_metadata' do
     let(:ref) { 'master' }
     let(:storage_path) { '/tmp' }