Merge branch 'add-repository-find-branch' into 'master'

Add Repository#find_branch to speed up branch lookups

See merge request !119

CHANGELOG

+v 10.5.0
+  - Add Repository#find_branch to speed up branch lookups
+  - Add Repository#reload_rugged to force a refresh of the Rugged repository
+
 v 10.4.7
   - Remove unneeded call to Repository#root_ref

lib/gitlab_git/repository.rb

@@ -70,6 +70,24 @@ module Gitlab
         end.compact.sort_by(&:name)
       end
+      def reload_rugged
+        @rugged = nil
+      end
+
+      # Directly find a branch with a simple name (e.g. master)
+      #
+      # force_reload causes a new Rugged repository to be instantiated
+      #
+      # This is to work around a bug in libgit2 that causes in-memory refs to
+      # be stale/invalid when packed-refs is changed.
+      # See https://gitlab.com/gitlab-org/gitlab-ce/issues/15392#note_14538333
+      def find_branch(name, force_reload = false)
+        reload_rugged if force_reload
+
+        rugged_ref = rugged.branches[name]
+        Branch.new(self, rugged_ref.name, rugged_ref.target) if rugged_ref
+      end
+
       def local_branches
         rugged.branches.each(:local).map do |branch|
           Branch.new(self, branch.name, branch.target)

spec/repository_spec.rb

@@ -813,6 +813,31 @@ describe Gitlab::Git::Repository do
     end
   end
+  describe '#find_branch' do
+    it 'should return a Branch for master' do
+      branch = repository.find_branch('master')
+
+      expect(branch).to be_a_kind_of(Gitlab::Git::Branch)
+      expect(branch.name).to eq('master')
+    end
+
+    it 'should handle non-existent branch' do
+      branch = repository.find_branch('this-is-garbage')
+
+      expect(branch).to eq(nil)
+    end
+
+    it 'should reload Rugged::Repository and return master' do
+      expect(Rugged::Repository).to receive(:new).twice.and_call_original
+
+      branch = repository.find_branch('master')
+      branch = repository.find_branch('master', force_reload: true)
+
+      expect(branch).to be_a_kind_of(Gitlab::Git::Branch)
+      expect(branch.name).to eq('master')
+    end
+  end
+
   describe '#branches with deleted branch' do
     before(:each) do
       ref = double()