eq-without-hash check removed

[jolaf]

Bug description

class A:
    def __init__(self) -> None:
        self.x = 5

    def __eq__(self, other: object) -> bool:
        return isinstance(other, A) and other.x == self.x

Configuration

No response

Command used

pylint test.py

Pylint output

empty

Expected behavior

Formerly eq-without-hash error was issued, but no more since pylint 2.11.

Pylint version

pylint 2.11.1
astroid 2.8.0
Python 3.8.10 (default, Jun  2 2021, 10:49:15) 
[GCC 9.4.0]

OS / Environment

Ubuntu 20.04.3 LTS \n \l

Additional dependencies

No response

[cdce8p]

The warning was removed as part of #4942.
@Pierre-Sassoulas What do you think? Maybe this should be added back as an optional checker?

https://docs.python.org/3/reference/datamodel.html#object.__hash__

[jolaf]

I saw #4942, but in Python 3, automatic reset of __hash__ to None if __eq__ is defined is non-trivial behavior that may cause hard-to-catch bugs.
I think its pretty reasonable to have a capability to warn about such things.
Even more so as this check was already present.
In other words, from my point of view, this check is usable even in strictly Python 3 context.

I didn't check, but I suspect some other checks that were introduced for checking the correctness of porting, and are now removed, are in fact pretty useful in Python 3-only code too.

[cdce8p]

@jolaf I went looked through the list twice, once for the review and the second time for your issue. eq-without-hash is the only one I know about now, all others seem to check for Python 2 behavior that isn't possible in Python 3. Tbh I haven't used Python 2, so it might be possible that I missed others. You can find the list here:
https://github.com/PyCQA/pylint/pull/4942/files#diff-34a57926d10bd84d60b6ddceb5447be233469d5e4e097ce7e5ecd64287fc5899L188-L608

Keep in mind that all of them had been disabled by default already. Your issue is the first one we've gotten about this.

[jolaf]

@cdce8p Yeah, I think you're right.
I've now also checked the list (thanks for the clear link) and found no other cases raising suspicions.

[Pierre-Sassoulas]

Let's move that to an existing checker, I think it could even be a default check ? Thank you for pointing that out @jolaf I did not use it myself as everything in the python3 porting checker was disabled by default.

[ghpqans]

Why is this and other options still present in the documentation for pylint 2.16 if it became deprecated since 2.11?
https://pylint.pycqa.org/en/latest/user_guide/messages/warning/eq-without-hash.html

Please reopen the issue. Seems like a documentation bug.

[Pierre-Sassoulas]

It was restored in #5843 following this very issue that argue for it to be reinstated.

[ghpqans]

Seems to be still present in the pypi package repo, from where I installed pylint:

(venv) user@l-user:~/PycharmProjects/my_project$ pylint --version
pylint 2.15.5

[...]
.pylintrc:1:0: R0022: Useless option value for '--disable', 'deprecated-operator-function' was removed from pylint, see https://github.com/PyCQA/pylint/pull/4942. (useless-option-value)
.pylintrc:1:0: R0022: Useless option value for '--disable', 'deprecated-urllib-function' was removed from pylint, see https://github.com/PyCQA/pylint/pull/4942. (useless-option-value)
.pylintrc:1:0: R0022: Useless option value for '--disable', 'xreadlines-attribute' was removed from pylint, see https://github.com/PyCQA/pylint/pull/4942. (useless-option-value)
.pylintrc:1:0: R0022: Useless option value for '--disable', 'deprecated-sys-function' was removed from pylint, see https://github.com/PyCQA/pylint/pull/4942. (useless-option-value)
.pylintrc:1:0: R0022: Useless option value for '--disable', 'exception-escape' was removed from pylint, see https://github.com/PyCQA/pylint/pull/4942. (useless-option-value)
.pylintrc:1:0: R0022: Useless option value for '--disable', 'comprehension-escape' was removed from pylint, see https://github.com/PyCQA/pylint/pull/4942. (useless-option-value)
.pylintrc:1:0: W0012: Unknown option value for '--disable', expected a valid pylint message and got 'long-suffix' (unknown-option-value)
.pylintrc:1:0: W0012: Unknown option value for '--disable', expected a valid pylint message and got 'old-ne-operator' (unknown-option-value)
.pylintrc:1:0: W0012: Unknown option value for '--disable', expected a valid pylint message and got 'old-octal-literal' (unknown-option-value)
.pylintrc:1:0: W0012: Unknown option value for '--disable', expected a valid pylint message and got 'non-ascii-bytes-literal' (unknown-option-value)
!---->> .pylintrc:1:0: W0012: Unknown option value for '--disable', expected a valid pylint message and got 'eq-without-hash' (unknown-option-value)

[Pierre-Sassoulas]

You need to activate the corresponding extension now, see notes from the link you pasted:

This message is emitted by the optional 'eq-without-hash' checker which requires the pylint.extensions.eq_without_hash plugin to be loaded.