False-positive signature-differs / arguments-differ with typing.overload

[cdce8p]

Bug description

Noticed that one while working on pylint-dev/astroid#1217 with @DanielNoord.

The logic for signature-differs / arguments-differ can't handle function redefinitions as its common with typing.overload. In particular I narrowed it down to two issue:

1. All function definitions seem to be check, even those decorated with overload.
2. The point of comparison is always the first definition, even if that isn't the true signature.

--
The examples require Python 3.8 (due to the use of typing.Literal). Not that they aren'T necessarily typed correctly. Just for illustration proposes.

Example 1

# pylint: disable=unused-argument,no-self-use,missing-docstring
from typing import Literal, Union, overload

class Parent:
    @overload
    def statement(self) -> int:
        ...

    @overload
    def statement(self, future: Literal[True]) -> str:
        ...

    def statement(self, future: Literal[None, True] = None) -> Union[int, str]:
        pass


class Child(Parent):
    # Signature comparison happens with first definition - the overload
    # Should use the actual function instead!
    def statement(self, future=None):  # arguments-differ (false-positive)
        pass

Example 2

# pylint: disable=unused-argument,no-self-use,missing-docstring
from typing import Literal, Union, overload

class Parent2:
    def statement(self, future: Literal[None, True] = None) -> Union[int, str]:
        pass

class Child2(Parent2):
    @overload
    def statement(self, future: Literal[None] = ...) -> int:
        ...

    @overload
    def statement(self, future: Literal[True]) -> str:  # signature-differs (false-positive)
        # Even overloads are checked although these aren't required
        # to have the correct signature
        ...

    def statement(self, future: Literal[None, True] = None) -> Union[int, str]:
        pass

Configuration

No response

Command used

pylint test.py

Pylint output

W0221: Number of parameters was 1 in 'Parent.statement' and is now 2 in overridden 'Child.statement' method (arguments-differ)

W0222: Signature differs from overridden 'statement' method (signature-differs)

Expected behavior

no errors

Pylint version

2.11.2-dev0

OS / Environment

No response

Additional dependencies

No response

[DanielNoord]

@cdce8p I narrowed down the issue with selecting the first overload instead of the actual signature due to the __getitem__ method of LocalsDictNodeNG in astroid. See:
https://github.com/PyCQA/astroid/blob/e3730a7aaf35030edcafbb5ec0509fb8ff070e33/astroid/nodes/scoped_nodes.py#L316-L324

This returns self.locals[item][0]. For overload this doesn't make sense and should probably be self.locals[item][-1]. I wonder if any other checks actually need to use [0]: if there are multiple definitions of a method in a class definition won't the last one be used anyway?

Do we want to fix this in astroid by changing the __getitem__ method (either by checking if decorated with overload, or changing for all methods) or do we want to create a workaround in pylint?

[Pierre-Sassoulas]

The first example was fixed in 2.15.0-dev0, not the second one.