Make GitLab use Gitaly for commit_is_ancestor

- Migration in Repository#is_ancestor?

app/models/repository.rb

@@ -981,7 +981,13 @@ class Repository
   end
 
   def is_ancestor?(ancestor_id, descendant_id)
-    merge_base(ancestor_id, descendant_id) == ancestor_id
+    Gitlab::GitalyClient.migrate(:is_ancestor) do |is_enabled|
+      if is_enabled
+        raw_repository.is_ancestor?(ancestor_id, descendant_id)
+      else
+        merge_base_commit(ancestor_id, descendant_id) == ancestor_id
+      end
+    end
   end
 
   def empty_repo?

changelogs/unreleased/feature-use-gitaly-for-commit-is-ancestor.yml

+---
+title: Use Gitaly for Repository#is_ancestor
+merge_request: 9864
+author:

lib/gitlab/git/repository.rb

@@ -406,6 +406,11 @@ module Gitlab
         rugged.merge_base(from, to)
       end
 
+      # Returns true is +from+ is direct ancestor to +to+, otherwise false
+      def is_ancestor?(from, to)
+        Gitlab::GitalyClient::Commit.is_ancestor(self, from, to)
+      end
+
       # Return an array of Diff objects that represent the diff
       # between +from+ and +to+.  See Diff::filter_diff_options for the allowed
       # diff options.  The +options+ hash can also include :break_rewrites to

lib/gitlab/gitaly_client/commit.rb

@@ -21,6 +21,20 @@ module Gitlab
 
           Gitlab::Git::DiffCollection.new(stub.commit_diff(request), options)
         end
+
+        def is_ancestor(repository, ancestor_id, child_id)
+          project = Project.find_by_path(repository.path)
+          channel = GitalyClient.get_channel(project.repository_storage)
+          stub = Gitaly::Commit::Stub.new(nil, nil, channel_override: channel)
+          repo = Gitaly::Repository.new(path: repository.path_to_repo)
+          request = Gitaly::CommitIsAncestorRequest.new(
+            repository: repo,
+            ancestor_id: ancestor_id,
+            child_id: child_id
+          )
+
+          stub.commit_is_ancestor(request).value
+        end
       end
     end
   end

spec/models/repository_spec.rb

@@ -1851,4 +1851,17 @@ describe Repository, models: true do
       end
     end
   end
+
+  describe '#is_ancestor?' do
+    context 'Gitaly is_ancestor feature enabled' do
+      it 'asks Gitaly server if it\'s an ancestor' do
+        commit = repository.commit
+        allow(Gitlab::GitalyClient).to receive(:feature_enabled?).with(:is_ancestor).and_return(true)
+        expect(Gitlab::GitalyClient::Commit).to receive(:is_ancestor).
+          with(repository.raw_repository, commit.id, commit.id).and_return(true)
+
+        expect(repository.is_ancestor?(commit.id, commit.id)).to be true
+      end
+    end
+  end
 end