Add `bad-dunder-name` extension checker (#7642)

With a 'good-dunder-name' option 

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

1 files changed, 77 insertions, 0 deletions

diff --git a/pylint/extensions/dunder.py b/pylint/extensions/dunder.py
new file mode 100644
index 000000000..e0e9af316
--- /dev/null
+++ b/pylint/extensions/dunder.py
@@ -0,0 +1,77 @@
+# 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
+
+from typing import TYPE_CHECKING
+
+from astroid import nodes
+
+from pylint.checkers import BaseChecker
+from pylint.constants import DUNDER_METHODS, DUNDER_PROPERTIES, EXTRA_DUNDER_METHODS
+from pylint.interfaces import HIGH
+
+if TYPE_CHECKING:
+    from pylint.lint import PyLinter
+
+
+class DunderChecker(BaseChecker):
+    """Checks related to dunder methods."""
+
+    name = "dunder"
+    priority = -1
+    msgs = {
+        "W3201": (
+            "Bad or misspelled dunder method name %s.",
+            "bad-dunder-name",
+            "Used when a dunder method is misspelled or defined with a name "
+            "not within the predefined list of dunder names.",
+        ),
+    }
+    options = (
+        (
+            "good-dunder-names",
+            {
+                "default": [],
+                "type": "csv",
+                "metavar": "<comma-separated names>",
+                "help": "Good dunder names which should always be accepted.",
+            },
+        ),
+    )
+
+    def open(self) -> None:
+        self._dunder_methods = (
+            EXTRA_DUNDER_METHODS
+            + DUNDER_PROPERTIES
+            + self.linter.config.good_dunder_names
+        )
+        for since_vers, dunder_methods in DUNDER_METHODS.items():
+            if since_vers <= self.linter.config.py_version:
+                self._dunder_methods.extend(list(dunder_methods.keys()))
+
+    def visit_functiondef(self, node: nodes.FunctionDef) -> None:
+        """Check if known dunder method is misspelled or dunder name is not one
+        of the pre-defined names.
+        """
+        # ignore module-level functions
+        if not node.is_method():
+            return
+
+        # Detect something that could be a bad dunder method
+        if (
+            node.name.startswith("_")
+            and node.name.endswith("_")
+            and node.name not in self._dunder_methods
+        ):
+            self.add_message(
+                "bad-dunder-name",
+                node=node,
+                args=(node.name),
+                confidence=HIGH,
+            )
+
+
+def register(linter: PyLinter) -> None:
+    linter.register_checker(DunderChecker(linter))