code: def changed_files(cls, scm, changes_since=None, diffspec=None):
      
      workspace = ScmWorkspace(scm)
      if diffspec:
        return workspace.changes_in(diffspec)
  
      changes_since = changes_since or scm.current_rev_identifier()
      return workspace.touched_files(changes_since)
docs: Determines the files changed according to SCM/workspace and options.