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You'd also need to update the new multiprocessing code - it currently expects "__main__.__spec__ == None" for all the run-from-a-path-or-stdin cases.
The -m switch and running __main__ from a supplied sys.path entry (the "dir" entry in your table) are both already handled by the runpy changes in issue 19700.
The remaining cases where __main__.__spec__ is currently None:
- interactive prompt
- -c switch
- running from stdin
- running directly from a source or bytecode file
To be honest, I'm not sure it actually makes sense to try to manufacture a pseudo-spec for those cases. A main script may not be importable as a module (e.g. a hyphen in its name, or no .py suffix), and you *definitely* can't import a file that doesn't exist on disk (REPL, stdin, -c).