False-positive no-untyped-def with @overload

[bersbersbers]

Bug Report

I get a false-positive no-untyped-def on the non-@overload-decorated definition.

To Reproduce

Example from PEP 484:

In regular modules, a series of @overload-decorated definitions must be followed by exactly one non-@overload-decorated definition (for the same function/method).

"""False-positive no-untyped-def."""
from typing import overload

@overload
def utf8(value: None) -> None:
    ...

@overload
def utf8(value: bytes) -> bytes:
    ...

def utf8(value):
    print(value)

Expected Behavior

No error.

Actual Behavior

bug.py:15: error: Function is missing a type annotation
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.982
• Mypy command-line flags: --disallow-untyped-defs (!)
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.7

[JelleZijlstra]

mypy is correct here. We need annotations on the overload implementation so that we can type check its body.

[bersbersbers]

We need annotations on the overload implementation so that we can type check its body.

Hm - I wonder why mypy does not simply check the body once for each overload.

Anyway, assuming we can ignore PEP 484, I wonder how to implement this correctly. I mean, the point of the overloads is to separate disjoint sets of argument types, so it seems somewhat pointless to combine them again into a single type annotation that covers all overloads. Here's an example that does not work, but maybe I am approaching it the wrong way:

from typing import Callable, overload

@overload
def pass_value_to_func(func: Callable[[float], None], value: float) -> None: ...
@overload
def pass_value_to_func(func: Callable[[int], None], value: int) -> None: ...

def pass_value_to_func(func: Callable[[float], None] | Callable[[int], None], value: float | int) -> None:
    func(value)

def print_float(value: float) -> None:
    print(value)

def print_int(value: int) -> None:
    print(value)

pass_value_to_func(print_float, 1.0)
pass_value_to_func(print_int, 1)

bug.py:9: error: Argument 1 has incompatible type "Union[float, int]"; expected "int"
Found 1 error in 1 file (checked 1 source file)

[hauntsaninja]

Duplicate of #3360