Summary

@no_type_check promises to suppress errors in a function declaration and body, but diagnostics emitted during post-inference function validation were not suppressed:

from typing import no_type_check

@no_type_check
def positional(x: int, __y: str): ...

Post-inference validation runs from the function's enclosing inference context, so the decorated function is not visible through the usual ancestor-scope suppression check. This returns before running those declaration checks when the function itself has a known @no_type_check decorator.