Incompatible return value when using union bound for generic function (false positive)

[RomanValov]

Bug Report

Using union as a bound for generic function type parameter T.
Function takes one argument of type type[T] and returns T.
mypy cannot infer equivalence between instance of type[T] and return type T.

The error is not reproduced if:

• single concrete type is used for bound (func[T: int])
• no bound used (func[T])

To Reproduce

def func[T: bool | int | float | str](ftype: type[T], value: str | None) -> T:
 if value is None:
 return ftype()
 return ftype(value)


if __name__ == '__main__':
 print(func(bool, 'True'))
 print(func(bool, None))
 print(func(int, '1'))
 print(func(int, None))
 print(func(float, '1.0'))
 print(func(float, None))
 print(func(str, 'test'))
 print(func(str, None))

https://mypy-play.net/?mypy=latest&python=3.12&gist=3bc312ee3a5620cbd789bfa1c93152ec

Expected Behavior

No errors

Actual Behavior

main.py:3: error: Incompatible return value type (got "int | float | str", expected "T") [return-value]
main.py:4: error: Incompatible return value type (got "int | float | str", expected "T") [return-value]

Your Environment

• Mypy version used: 1.19.1
• Python version used: 3.12