Unclear error message: incompatible type "type[str]"; expected "Callable[[_T], _T]"

To Reproduce

from collections.abc import Sequence
from typing import TypeVar

_T = TypeVar("_T")

def foo(seq: Sequence[_T]) -> None:
    seq = tuple(map(str, seq))

$ mypy ./mypy_bug.py
mypy_bug.py: note: In function "foo":
mypy_bug.py:7:19: error: Argument 1 to "map" has incompatible type "type[str]"; expected "Callable[[_T], _T]"
[arg-type]
      seq = tuple(map(str, seq))
                      ^~~
Found 1 error in 1 file (checked 1 source file)

Interestingly enough, this error does not fire if you assign to something other than seq:

def foo(seq: Sequence[_T]) -> None:
    not_seq = tuple(map(str, seq))  # no problem, no mypy error

• Mypy version used: mypy 1.9.0 (compiled: yes)
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: Python 3.12.2

まず mypy_bug.py の最小例を mypy で実行し、seq への代入と not_seq への同等の代入を比較します。これら 2 つのコンテキストで、型チェッカーが map の callable 引数をどのように推論するかを追跡します。不整合な診断が解消され、再現ケースにリグレッションテストのカバレッジが追加されれば完了です。