docs: def trace_toolchain(toolchain):
      """
      Trace the versions of the involved packages for the provided
      toolchain instance.
      """
  
      pkgs = []
      for cls in getmro(type(toolchain)):
          if not issubclass(cls, Toolchain):
              continue
          dist = _cls_lookup_dist(cls)
          value = {
              'project_name': dist.project_name,
              'version': dist.version,
          } if dist else {}
          key = '%s:%s' % (cls.__module__, cls.__name__)
          pkgs.append({key: value})
      return pkgs