You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: position.rb
    path of file: ./repos/gitlabhq/lib/gitlab/diff
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

# Defines a specific location, identified by paths l
    
      def diff_file(repository)
        return @diff_file if defined?(@diff_file)

        @diff_file = begin
          key = {
            project_id: repository.project.id,
            start_sha: start_sha,
            head_sha: head_sha,
            path: file_path
          }

          # Takes action when creating diff notes (multiple calls are
          # submitted to this method).
          Gitlab::SafeRequestStore.fetch(key) { find_diff_file(repository) }
        end