code: def diff_commit(self, commit, compare_point=None):
          
          # @@@ This is a security hazard as compare-point is user-passed in
          # data. Doesn't matter until we wrap this in a service.
          if compare_point is not None:
              self.apply_commit(compare_point)
          return self.executor("cd %s && git diff %s" % (self.dirname, commit))
docs: Returns a diff as a string from the current HEAD to the given commit.