Cannot assert a callable returns `None` when it must return `None`

Bug Report

mypy prevents you making assertions about callables that must return None when they're called.
This is important as not everyone works in a type-checked context, and so library code must be robust to this.
In my case, I have a chain of callables, the ones in the middle take iterables and return iterables, but the one at the start must take no arguments and the one at the end must consume the upstream iterable and return nothing.

To Reproduce

def returns_none() -> None:
    pass

assert returns_none() is None

Expected Behavior

No mypy complaints

Actual Behavior

"returns_none" does not return a value (it only ever returns None) [func-returns-value]

Your Environment

• Mypy version used: mypy 1.10.1 (compiled: yes)
• Mypy command-line flags: none
• Python version used: Python 3.12.1

示されている returns_none 関数とアサーションを使用して、Python 3.12.1 上の mypy 1.10.1 で報告を再現します。func-returns-value 診断を追跡し、その後、None を返すとアノテーションされた callable に関するアサーションでは何も報告されず、不適切な値の使用に対する既存の診断は残ることを確認します。