Even with setting SourceFileLoader, you still don't get file lines back. Why? Because all of the constructed objects in _frozen_importlib have their co_filename set before the back-patching in importlib.__init__ and so when the traceback module tries to do its thing it sees '<frozen importlib._bootstrap>' as the filename instead of importlib._bootstrap.__file__ which doesn't lead to linecache getting anything useful.

IOW a whole lot of effort for code that people should never have to look at.