TypedDict.setdefault gives error when type is a TypeVar

[bmerry]

Bug Report

When a function argument is annotated using a TypeVar with a bound that is a TypedDict, using setdefault on it leads to an error.

To Reproduce

from typing import TypedDict, TypeVar

class TD(TypedDict, total=False):
    foo: int
    bar: bool

_T = TypeVar("_T", bound=TD)

def func(td: _T) -> None:
    td.setdefault("bar", True)

Actual Behavior

testit.py:10: error: Argument 1 to "setdefault" of "TypedDict" has incompatible type "str"; expected "Never"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: mypy 1.11.1 (compiled: yes)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): no config file
• Python version used: 3.12.3