Default branch detection happens through Gitaly

Migration: https://gitlab.com/gitlab-org/gitaly/issues/220

lib/gitlab/git/repository.rb

@@ -120,13 +120,11 @@ module Gitlab
 
       # Default branch in the repository
       def root_ref
-        @root_ref ||= gitaly_migrate(:root_ref, status: Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |is_enabled|
-          if is_enabled
-            gitaly_ref_client.default_branch_name
-          else
-            discover_default_branch
-          end
-        end
+        gitaly_ref_client.default_branch_name
+      rescue GRPC::NotFound => e
+        raise NoRepository.new(e.message)
+      rescue GRPC::Unknown => e
+        raise Gitlab::Git::CommandError.new(e.message)
       end
 
       def rugged
@@ -364,31 +362,6 @@ module Gitlab
         end.map(&:name)
       end
 
-      # Discovers the default branch based on the repository's available branches
-      #
-      # - If no branches are present, returns nil
-      # - If one branch is present, returns its name
-      # - If two or more branches are present, returns current HEAD or master or first branch
-      def discover_default_branch
-        names = branch_names
-
-        return if names.empty?
-
-        return names[0] if names.length == 1
-
-        if rugged_head
-          extracted_name = Ref.extract_branch_name(rugged_head.name)
-
-          return extracted_name if names.include?(extracted_name)
-        end
-
-        if names.include?('master')
-          'master'
-        else
-          names[0]
-        end
-      end
-
       def rugged_head
         rugged.head
       rescue Rugged::ReferenceError

spec/lib/gitlab/git/repository_spec.rb

@@ -77,17 +77,6 @@ describe Gitlab::Git::Repository, seed_helper: true do
   end
 
   describe '#root_ref' do
-    context 'with gitaly disabled' do
-      before do
-        allow(Gitlab::GitalyClient).to receive(:feature_enabled?).and_return(false)
-      end
-
-      it 'calls #discover_default_branch' do
-        expect(repository).to receive(:discover_default_branch)
-        repository.root_ref
-      end
-    end
-
     it 'returns UTF-8' do
       expect(repository.root_ref).to be_utf8
     end
@@ -153,46 +142,6 @@ describe Gitlab::Git::Repository, seed_helper: true do
     end
   end
 
-  describe "#discover_default_branch" do
-    let(:master) { 'master' }
-    let(:feature) { 'feature' }
-    let(:feature2) { 'feature2' }
-
-    around do |example|
-      # discover_default_branch will be moved to gitaly-ruby
-      Gitlab::GitalyClient::StorageSettings.allow_disk_access do
-        example.run
-      end
-    end
-
-    it "returns 'master' when master exists" do
-      expect(repository).to receive(:branch_names).at_least(:once).and_return([feature, master])
-      expect(repository.discover_default_branch).to eq('master')
-    end
-
-    it "returns non-master when master exists but default branch is set to something else" do
-      File.write(File.join(repository_path, 'HEAD'), 'ref: refs/heads/feature')
-      expect(repository).to receive(:branch_names).at_least(:once).and_return([feature, master])
-      expect(repository.discover_default_branch).to eq('feature')
-      File.write(File.join(repository_path, 'HEAD'), 'ref: refs/heads/master')
-    end
-
-    it "returns a non-master branch when only one exists" do
-      expect(repository).to receive(:branch_names).at_least(:once).and_return([feature])
-      expect(repository.discover_default_branch).to eq('feature')
-    end
-
-    it "returns a non-master branch when more than one exists and master does not" do
-      expect(repository).to receive(:branch_names).at_least(:once).and_return([feature, feature2])
-      expect(repository.discover_default_branch).to eq('feature')
-    end
-
-    it "returns nil when no branch exists" do
-      expect(repository).to receive(:branch_names).at_least(:once).and_return([])
-      expect(repository.discover_default_branch).to be_nil
-    end
-  end
-
   describe '#branch_names' do
     subject { repository.branch_names }