[Regression 1.6.x -> 1.7] Invalid "Returning Any from function declared..."

[inducer]

To Reproduce

from __future__ import annotations
from functools import partialmethod
import operator
from typing import Any, Union

ScalarType = Union[int, bool, float]
ArrayOrScalar = Union["Array", ScalarType]


class Array:
    def _binary_op(self,
            op: Any,
            other: ArrayOrScalar,
            ) -> Array:

        return Array()

    __mul__ = partialmethod(_binary_op, operator.mul)


def dot(a: ArrayOrScalar, b: ArrayOrScalar) -> ArrayOrScalar:
    assert isinstance(a, Array)
    assert isinstance(b, Array)

    return a * b

Expected Behavior

Type-checks correctly, as it does with 1.6.1.

Actual Behavior

/home/andreas/tmp/mypy-array-repro.py:30: error: Returning Any from function declared to return "Array | int | bool | float"  [no-any-return]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.7.0 (compiled: yes)
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.12

[ilevkivskyi]

OK, the problem is that partialmethod has an overloaded constructor, and mypy has a rule that if an argument matches multiple overloads with different (inferred) return types, and this argument contains an Any type, then the inferred return type will be also "erased". Although this rule is weird, it has certain good reasons, so technically current behavior is expected.

FWIW there is an easy fix, use object instead of Any here:

    def _binary_op(self,
            op: object,  # <-- here
            other: ArrayOrScalar,
            ) -> Array:

        return Array()

this fixes the problem

[inducer]

Thanks for responding! I agree that the workaround you provide does address the issue for the reproducer I provided, however unfortunately that is not the case in the full-scale code from which the reproducer is derived. Specifically I am talking about this error:

pytato/array.py:2533: error: Returning Any from function declared to return "Array | number[Any] | int | bool_ | bool | float"  [no-any-return]

being reported for this commit of the full-scale thing:

inducer/pytato@a8f380f

I have not yet succeeded in making a smaller reproducer that still shows the issue.

[inducer]

FWIW, the corresponding bits of the full-scale code are here:

https://github.com/inducer/pytato/blob/86a55ba423b013150e63b5d6cdc11bc29eabb00f/pytato/array.py#L528-L568

for the call to partialmethod (and the method on which it is being used) and here:

https://github.com/inducer/pytato/blob/86a55ba423b013150e63b5d6cdc11bc29eabb00f/pytato/array.py#L2533

for the affected call site being reported.