message: Explicit copy assertion.
diff: @@ -3189,7 +3189,9 @@ def __copy_stripped(source, to, strip_prefix, builder, post_process, follow_syml
  __copy_stripped_cache[key] = res
  return res
  res = builder(source, path, post_process, follow_symlinks).target
  - assert res is not source
  + if res is source:
  + raise Exception(
  + 'copy source and destination are the same: %s', res)
  for dep in source.dependencies:
  if not dep.name_absolute().absolute():
  node = __copy_stripped(dep, to, strip_prefix, builder, post_process, follow_symlinks)
  