Add `magic-number` checker for comparison with literals (#7526)

Co-authored-by: Or Bahari <or.bahari@samsung.com>

1 files changed, 88 insertions, 0 deletions

diff --git a/pylint/extensions/magic_value.py b/pylint/extensions/magic_value.py
new file mode 100644
index 000000000..161bb2c95
--- /dev/null
+++ b/pylint/extensions/magic_value.py
@@ -0,0 +1,88 @@
+# 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
+
+"""Checks for magic values instead of literals."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from astroid import nodes
+
+from pylint.checkers import BaseChecker, utils
+from pylint.interfaces import HIGH
+
+if TYPE_CHECKING:
+    from pylint.lint import PyLinter
+
+
+class MagicValueChecker(BaseChecker):
+    """Checks for constants in comparisons."""
+
+    name = "magic-value"
+    msgs = {
+        "R2004": (
+            "Consider using a named constant or an enum instead of '%s'.",
+            "magic-value-comparison",
+            "Using named constants instead of magic values helps improve readability and maintainability of your"
+            " code, try to avoid them in comparisons.",
+        )
+    }
+
+    options = (
+        (
+            "valid-magic-values",
+            {
+                "default": (0, -1, 1, "", "__main__"),
+                "type": "csv",
+                "metavar": "<argument names>",
+                "help": " List of valid magic values that `magic-value-compare` will not detect.",
+            },
+        ),
+    )
+
+    def _check_constants_comparison(self, node: nodes.Compare) -> None:
+        """
+        Magic values in any side of the comparison should be avoided,
+        Detects comparisons that `comparison-of-constants` core checker cannot detect.
+        """
+        const_operands = []
+        LEFT_OPERAND = 0
+        RIGHT_OPERAND = 1
+
+        left_operand = node.left
+        const_operands.append(isinstance(left_operand, nodes.Const))
+
+        right_operand = node.ops[0][1]
+        const_operands.append(isinstance(right_operand, nodes.Const))
+
+        if all(const_operands):
+            # `comparison-of-constants` avoided
+            return
+
+        operand_value = None
+        if const_operands[LEFT_OPERAND] and self._is_magic_value(left_operand):
+            operand_value = left_operand.value
+        elif const_operands[RIGHT_OPERAND] and self._is_magic_value(right_operand):
+            operand_value = right_operand.value
+        if operand_value is not None:
+            self.add_message(
+                "magic-value-comparison",
+                node=node,
+                args=(operand_value),
+                confidence=HIGH,
+            )
+
+    def _is_magic_value(self, node: nodes.NodeNG) -> bool:
+        return (not utils.is_singleton_const(node)) and (
+            node.value not in self.linter.config.valid_magic_values
+        )
+
+    @utils.only_required_for_messages("magic-comparison")
+    def visit_compare(self, node: nodes.Compare) -> None:
+        self._check_constants_comparison(node)
+
+
+def register(linter: PyLinter) -> None:
+    linter.register_checker(MagicValueChecker(linter))