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✏️ Editing: implicit_booleaness_checker.py

# 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

from __future__ import annotations

import astroid
from astroid import bases, nodes, util

from pylint import checkers
from pylint.checkers import utils
from pylint.interfaces import HIGH, INFERENCE

class ImplicitBooleanessChecker(checkers.BaseChecker):
    """Checks for incorrect usage of comparisons or len() inside conditions.

Incorrect usage of len()
    Pep8 states:
    For sequences, (strings, lists, tuples), use the fact that empty sequences are false.

Yes: if not seq:
             if seq:

No: if len(seq):
            if not len(seq):

Problems detected:
    * if len(sequence):
    * if not len(sequence):
    * elif len(sequence):
    * elif not len(sequence):
    * while len(sequence):
    * while not len(sequence):
    * assert len(sequence):
    * assert not len(sequence):
    * bool(len(sequence))

Incorrect usage of empty literal sequences; (), [], {},

For empty sequences, (dicts, lists, tuples), use the fact that empty sequences are false.

Yes: if variable:
             if not variable

No: if variable == empty_literal:
            if variable != empty_literal:

Problems detected:
    * comparison such as variable == empty_literal:
    * comparison such as variable != empty_literal:
    """

name = "refactoring"
    msgs = {
        "C1802": (
            "Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty",
            "use-implicit-booleaness-not-len",
            "Used when Pylint detects that len(sequence) is being used "
            "without explicit comparison inside a condition to determine if a sequence is empty. "
            "Instead of coercing the length to a boolean, either "
            "rely on the fact that empty sequences are false or "
            "compare the length against a scalar.",
            {"old_names": [("C1801", "len-as-condition")]},
        ),
        "C1803": (
            "'%s' can be simplified to '%s' as an empty %s is falsey",
            "use-implicit-booleaness-not-comparison",
            "Used when Pylint detects that collection literal comparison is being "
            "used to check for emptiness; Use implicit booleaness instead "
            "of a collection classes; empty collections are considered as false",
        ),
    }

options = ()

@utils.only_required_for_messages("use-implicit-booleaness-not-len")
    def visit_call(self, node: nodes.Call) -> None:
        # a len(S) call is used inside a test condition
        # could be if, while, assert or if expression statement
        # e.g. `if len(S):`
        if not utils.is_call_of_name(node, "len"):
            return
        # the len() call could also be nested together with other
        # boolean operations, e.g. `if z or len(x):`
        parent = node.parent
        while isinstance(parent, nodes.BoolOp):
            parent = parent.parent
        # we're finally out of any nested boolean operations so check if
        # this len() call is part of a test condition
        if not utils.is_test_condition(node, parent):
            return
        len_arg = node.args[0]
        generator_or_comprehension = (
            nodes.ListComp,
            nodes.SetComp,
            nodes.DictComp,
            nodes.GeneratorExp,
        )
        if isinstance(len_arg, generator_or_comprehension):
            # The node is a generator or comprehension as in len([x for x in ...])
            self.add_message(
                "use-implicit-booleaness-not-len",
                node=node,
                confidence=HIGH,
            )
            return
        try:
            instance = next(len_arg.infer())
        except astroid.InferenceError:
            # Probably undefined-variable, abort check
            return
        mother_classes = self.base_names_of_instance(instance)
        affected_by_pep8 = any(
            t in mother_classes for t in ("str", "tuple", "list", "set")
        )
        if "range" in mother_classes or (
            affected_by_pep8 and not self.instance_has_bool(instance)
        ):
            self.add_message(
                "use-implicit-booleaness-not-len",
                node=node,
                confidence=INFERENCE,
            )

@staticmethod
    def instance_has_bool(class_def: nodes.ClassDef) -> bool:
        try:
            class_def.getattr("__bool__")
            return True
        except astroid.AttributeInferenceError:
            ...
        return False

@utils.only_required_for_messages("use-implicit-booleaness-not-len")
    def visit_unaryop(self, node: nodes.UnaryOp) -> None:
        """`not len(S)` must become `not S` regardless if the parent block is a test
        condition or something else (boolean expression) e.g. `if not len(S):`.
        """
        if (
            isinstance(node, nodes.UnaryOp)
            and node.op == "not"
            and utils.is_call_of_name(node.operand, "len")
        ):
            self.add_message(
                "use-implicit-booleaness-not-len", node=node, confidence=HIGH
            )

@utils.only_required_for_messages("use-implicit-booleaness-not-comparison")
    def visit_compare(self, node: nodes.Compare) -> None:
        self._check_use_implicit_booleaness_not_comparison(node)

def _check_use_implicit_booleaness_not_comparison(
        self, node: nodes.Compare
    ) -> None:
        """Check for left side and right side of the node for empty literals."""
        is_left_empty_literal = utils.is_base_container(
            node.left
        ) or utils.is_empty_dict_literal(node.left)

# Check both left-hand side and right-hand side for literals
        for operator, comparator in node.ops:
            is_right_empty_literal = utils.is_base_container(
                comparator
            ) or utils.is_empty_dict_literal(comparator)
            # Using Exclusive OR (XOR) to compare between two side.
            # If two sides are both literal, it should be different error.
            if is_right_empty_literal ^ is_left_empty_literal:
                # set target_node to opposite side of literal
                target_node = node.left if is_right_empty_literal else comparator
                literal_node = comparator if is_right_empty_literal else node.left
                # Infer node to check
                target_instance = utils.safe_infer(target_node)
                if target_instance is None:
                    continue
                mother_classes = self.base_names_of_instance(target_instance)
                is_base_comprehension_type = any(
                    t in mother_classes for t in ("tuple", "list", "dict", "set")
                )

# Only time we bypass check is when target_node is not inherited by
                # collection literals and have its own __bool__ implementation.
                if not is_base_comprehension_type and self.instance_has_bool(
                    target_instance
                ):
                    continue

# No need to check for operator when visiting compare node
                if operator in {"==", "!=", ">=", ">", "<=", "<"}:
                    self.add_message(
                        "use-implicit-booleaness-not-comparison",
                        args=self._implicit_booleaness_message_args(
                            literal_node, operator, target_node
                        ),
                        node=node,
                        confidence=HIGH,
                    )

def _get_node_description(self, node: nodes.NodeNG) -> str:
        return {
            nodes.List: "list",
            nodes.Tuple: "tuple",
            nodes.Dict: "dict",
            nodes.Const: "str",
        }.get(type(node), "iterable")

def _implicit_booleaness_message_args(
        self, literal_node: nodes.NodeNG, operator: str, target_node: nodes.NodeNG
    ) -> tuple[str, str, str]:
        """Helper to get the right message for "use-implicit-booleaness-not-comparison"."""
        description = self._get_node_description(literal_node)
        collection_literal = {
            "list": "[]",
            "tuple": "()",
            "dict": "{}",
        }.get(description, "iterable")
        instance_name = "x"
        if isinstance(target_node, nodes.Call) and target_node.func:
            instance_name = f"{target_node.func.as_string()}(...)"
        elif isinstance(target_node, (nodes.Attribute, nodes.Name)):
            instance_name = target_node.as_string()
        original_comparison = f"{instance_name} {operator} {collection_literal}"
        suggestion = f"{instance_name}" if operator == "!=" else f"not {instance_name}"
        return original_comparison, suggestion, description

@staticmethod
    def base_names_of_instance(
        node: util.UninferableBase | bases.Instance,
    ) -> list[str]:
        """Return all names inherited by a class instance or those returned by a
        function.

The inherited names include 'object'.
        """
        if isinstance(node, bases.Instance):
            return [node.name] + [x.name for x in node.ancestors()]
        return []

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