Add checker for comparing for equality to empty literal

[DanielNoord]

Current problem

Originally posted by @cdce8p in #4769 (comment)

Best not to check for equality by comparing it to an empty literal.
(This should probably be a pylint check as well.)

Desired solution

# good
test_list = []
if not test_list:
   pass

# bad
test_list = []
if test_list == []:
   pass

Additional context

No response

[cdce8p]

I already though of a way to implement it, but couldn't yet think of a good name or description. If anyone once to take a stab at it, this here should work:

    def visit_compare(self, node: astroid.Compare) -> None:
        for op, comparator in node.ops:
            if op == "==":
                if (
                    isinstance(comparator, (astroid.List, astroid.Tuple))
                    and not comparator.elts
                    or isinstance(comparator, astroid.Dict)
                    and not comparator.items
                ):
                    self.add_message(..., node=node)

[DanielNoord]

Perhaps no-empty-literal-comparison?
And what kind of message would this be? Does this have a performance effect? Or is it just code style?

[cdce8p]

Perhaps no-empty-literal-comparison?

Sounds like a start. I'm not good at naming things though 😅
@Pierre-Sassoulas Do you have a good idea?

And what kind of message would this be? Does this have a performance effect? Or is it just code style?

Maybe a small performance effect and a bit code style. So probably a refactoring checker.

[Pierre-Sassoulas]

Maybe use-implicit-booleanness or empty-literal-as-condition (based on the name of len-as-condition which is similar) ? This checker is prone to false positive because for numpy/pandas array the boolean value of an array is ambiguous. Ie you need to do not test_list.size or use all or any. Arguably test_list == [] could be considered better in that case (?). So I think we probably need to do something specifically for numpy/pandas. Something similar was done for len-as-condition where we check that the __bool__ function is not re-implemented and that the class inherit directly from a list, set, or dict (ie: not a ndarray), see #3821

[Pierre-Sassoulas]

I've been thinking: we could rename len-as-condition to use-implicit-booleanness and add the comparison to empty literal to the checker.

[DanielNoord]

Probably should also implement #3031 when working on this issue.

[jaehoonhwang]

Hi, can I try to resolve this issue?

[Pierre-Sassoulas]

Hi, @jaehoonhwang , of course, I'll assign you to the issue.