Return type for force_bytes() on protected types is incorrect

[mthuurne]

Bug report

What's wrong

When checking the following code:

from django.utils.encoding import force_bytes

b = force_bytes(123)
reveal_type(b)

mypy reports:

testcase.py:4: note: Revealed type is "builtins.int*"

How is that should be

Since the omitted strings_only argument is False by default, force_bytes() will convert the given int to str and then convert that str to bytes.

When I explicitly pass strings_only=False, mypy does report bytes as the returned type.

The stubs look like this:

@overload
def force_bytes(s: _PT, encoding: str = ..., strings_only: Literal[True] = ..., errors: str = ...) -> _PT: ...
@overload
def force_bytes(s: Any, encoding: str = ..., strings_only: bool = ..., errors: str = ...) -> bytes: ...

I thought that perhaps the problem is that mypy can't know the default value for strings_only, but adding False as an explicit default doesn't solve it.

I also tried exchanging the order of the two overload definitions, but while that fixes the testcase, it breaks when strings_only=True is passed, so that's not a solution.

Omitting the default is not an option either, because strings_only isn't a keyword-only argument and the encoding argument before it has a default value.

So I'm currently out of ideas for how this can be annotated in a way that makes mypy do the right thing.

System information

• OS: Ubuntu Linux 18.04
• python version: 3.9.7
• django version: 4.0.1
• mypy version: 0.931
• django-stubs version: current master (5d3768e)
• django-stubs-ext version: current master (5d3768e)