mypy rejects unpacking into same variable

Bug Report

I believe the following code should be fine, however mypy rejects the case where we're unpacking into the variable which was expanded:

foo: tuple[int, ...] = ()

# Ok
bar, *quox = foo

# Incompatible types in assignment (expression has type "List[int]", variable has type "Tuple[int, ...]")  [assignment]
bar, *foo = foo

There are a number of similar issues reported, the closest being https://github.com/python/mypy/issues/9706, however I believe this is distinct as it reproduces when the generic type is int (though my original code was using str). This suggests a different root cause.

Your Environment

• Mypy version used: 1.0.1
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10

まず、報告された Python 3.10 のスニペットを mypy 1.0.1 で実行し、展開される変数が同時にソースでもある場合に、アンパック代入がどのようにチェックされるかを追跡します。このケースの回帰テストを追加し、同じ変数のアンパックが受け入れられる一方で、互換性のない代入は引き続き診断されることを確認します。