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# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
# Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt

"""This is the remnant of the python3 checker.

It was removed because the transition from python 2 to python3 is
behind us, but some checks are still useful in python3 after all.
See https://github.com/PyCQA/pylint/issues/5025
"""

from astroid import nodes

from pylint import checkers, interfaces
from pylint.checkers import utils
from pylint.lint import PyLinter


class EqWithoutHash(checkers.BaseChecker):
    name = "eq-without-hash"

    msgs = {
        "W1641": (
            "Implementing __eq__ without also implementing __hash__",
            "eq-without-hash",
            "Used when a class implements __eq__ but not __hash__. Objects get "
            "None as their default __hash__ implementation if they also implement __eq__.",
        ),
    }

    @utils.only_required_for_messages("eq-without-hash")
    def visit_classdef(self, node: nodes.ClassDef) -> None:
        locals_and_methods = set(node.locals).union(x.name for x in node.mymethods())
        if "__eq__" in locals_and_methods and "__hash__" not in locals_and_methods:
            self.add_message("eq-without-hash", node=node, confidence=interfaces.HIGH)


def register(linter: PyLinter) -> None:
    linter.register_checker(EqWithoutHash(linter))