Respect sys.platform platform check assertion inside functions

This is a feature request

From the docs
https://mypy.readthedocs.io/en/stable/common_issues.html#python-version-and-system-platform-checks

More specifically, mypy will understand the use of sys.version_info and sys.platform checks
within if/elif/else statements.

and

As a special case, you can also use one of these checks in a top-level (unindented) assert; this makes mypy skip the rest of the file.

It would be nice if this kind of code would also typecheck on mac/linux.
Currently the option is to refactor such that you can define the entire function within an if sys.platform == "win32"

class A:
   def func_on_win_only() -> str:
      assert sys.platform == "win32"
      return sys.getwindowsversion()

Inizia riproducendo l’esempio su una piattaforma non Windows e leggi la documentazione di mypy collegata sui controlli di sys.platform. Traccia la gestione esistente delle asserzioni di primo livello, quindi aggiungi la copertura di regressione per un’asserzione all’interno di una funzione e verifica che la chiamata riservata a Windows superi il controllo dei tipi su macOS o Linux.