Internal checker for @utils.only_required_for_messages to verify that it's used when required and not used when not required

[Pierre-Sassoulas]

@utils.only_required_for_messages should be working for token based checker and a check to verify that it's used when required and not used when not required.

Originally posted by @Pierre-Sassoulas in #8606 (review)

[jacobtylerwalls]

Would you be able to flesh this out a little more for me? I didn't follow the comment in the review.

[Pierre-Sassoulas]

Sure, sorry ! Let me create a functional test example:

from typing import TYPE_CHECKING

from astroid import nodes

from pylint.checkers import BaseChecker
from pylint.checkers.utils import only_required_for_messages

if TYPE_CHECKING:
    from pylint.lint import PyLinter


class AnnoyingCodeGolfChecker(BaseChecker):
    name = "annoying_code_golf"
    msgs = {
        "W0149": (
            "Used `while` loop",
            "while-used",
            "blablabla.",
        )
        "W0150": (
            "Used `for` loop",
            "for-used",
            "blablabla.",
        )
        "W0151": (
            "Used `assignment`",
            "assignment-used",
            "blablabla.",
        )
        "W0152": (
            "Ideas are hard to come by after a point.",
            "another-message",
            "blablabla.",
        )
    }

    @only_required_for_messages("while-used", "for-used") 
    def visit_while(self, node: nodes.While) -> None:  # pylint-suboptimization
        """'for-used' is never added in this function"""
        self.add_message("while-used", node=node)

    def visit_for(self, node: nodes.For) -> None:   # pylint-suboptimization
        """only_required_for_messages not used for this function"""
        self.add_message("for-used", node=node)

    @only_required_for_messages("assignment-used") 
    def visit_assignment(self, node: nodes.Assign) -> None:   # pylint-overoptimization
        """Another message than assignment used is created in this function. 
        
        Admittedly this one is going to be detected by the documentation tests
        because it will be impossible to raise 'another-message' when 
        'assignment-used' is disabled."""
        self.add_message("assignment-used", node=node)
        self._sneakily_add_a_message(node)

    def _sneakily_add_a_message(self, node):
        self.add_message("another-message", node=node)

[DanielNoord]

Don't we have this on CI? The Linux runner already tests if we have decorated all methods correctly. We don't check for over-usage, but that isn't a big issue imo.

[Pierre-Sassoulas]

We also have some use of self.linter.is_message_enabled( (see example in the MR linked in the original issue text) because the only_required_for_messages decorator only works on visitor_x function.