Return type hint fails with multiple supplied type vars

Bug Report

I'm not 100% sure how to word this but mypy fails to detect the proper return type if multiple types are supplied. It works just fine if only a single type is specified.

This scenario works just fine with pyright/pylance.

To Reproduce

import typing as t


class BaseClass:
    ...


class Sub1(BaseClass):
    ...


class Sub2(BaseClass):
    ...


ClassType = t.TypeVar("ClassType", bound=BaseClass)


def testing_union() -> t.Union[Sub1, Sub2]:
    res = sub_method(Sub1, Sub2)
    reveal_type(res)

    return res


def testing_single() -> Sub1:
    res = sub_method(Sub1)

    return res


def sub_method(*output_type: t.Type[ClassType]) -> ClassType:
    return  # type: ignore[return-value]

Expected Behavior

I expect mypy to work for both testing_union() and testing_single().

Actual Behavior

A return-value occurs in testing_union as it thinks the value is the bound base class. Using reveal_type we can see that mypy detects the type as BaseClass whereas pylance/pyright detects it as the expect3ed Sub1 | Sub2 type.

The output from the mypy check is

mypy-test.py:21: note: Revealed type is "mypy-test.BaseClass"
mypy-test.py:23: error: Incompatible return value type (got "BaseClass", expected "Union[Sub1, Sub2]")  [return-value]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: mypy 1.0.0 (compiled: yes)
• Mypy command-line flags: python -m mypy file.py
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: Python 3.11.0

Beginne damit, den bereitgestellten Reproducer mit mypy 1.0.0 auszuführen, und vergleiche den aufgelösten Typ für mehrere gegenüber einzelnen Typargumenten. Verfolge das Verhalten der Typinferenz für die variadischen TypeVar-Argumente von sub_method; fertig ist es, wenn der Union-Fall Sub1 | Sub2 auflöst und die deklarierte Rückgabeprüfung besteht, ohne den Fall mit einem einzelnen Typ abzuschwächen.