# File lib/librarian/source/git/repository.rb, line 104
        def hash_from(remote, reference)
          branch_names = remote_branch_names[remote]
          if branch_names.include?(reference)
            reference = "#{remote}/#{reference}"
          end

          command = ??(rev-list #{reference} -1)
          run!(command, :chdir => true).strip
        end