[pylint] Implement bad-dunder-name (W3201) (#6486)

## Summary

Checks for any misspelled dunder name method and for any method defined
with `__...__` that's not one of the pre-defined methods.

The pre-defined methods encompass all of Python's standard dunder
methods.

ref: #970

## Test Plan
Snapshots and manual runs of pylint.

crates/ruff/resources/test/fixtures/pylint/bad_dunder_method_name.py

@@ -0,0 +1,46 @@
+class Apples:
+ def _init_(self): # [bad-dunder-name]
+ pass
+
+ def __hello__(self): # [bad-dunder-name]
+ print("hello")
+
+ def __init_(self): # [bad-dunder-name]
+ # author likely unintentionally misspelled the correct init dunder.
+ pass
+
+ def _init_(self): # [bad-dunder-name]
+ # author likely unintentionally misspelled the correct init dunder.
+ pass
+
+ def ___neg__(self): # [bad-dunder-name]
+ # author likely accidentally added an additional `_`
+ pass
+
+ def __inv__(self): # [bad-dunder-name]
+ # author likely meant to call the invert dunder method
+ pass
+
+ def hello(self):
+ print("hello")
+
+ def __init__(self):
+ pass
+
+ def init(self):
+ # valid name even though someone could accidentally mean __init__
+ pass
+
+ def _protected_method(self):
+ print("Protected")
+
+ def __private_method(self):
+ print("Private")
+
+ @property
+ def __doc__(self):
+ return "Docstring"
+
+
+def __foo_bar__(): # this is not checked by the [bad-dunder-name] rule
+ ...

crates/ruff/src/checkers/ast/analyze/statement.rs

@@ -509,6 +509,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
  if checker.enabled(Rule::SingleStringSlots) {
  pylint::rules::single_string_slots(checker, class_def);
  }
+ if checker.enabled(Rule::BadDunderMethodName) {
+ pylint::rules::bad_dunder_method_name(checker, body);
+ }
  }
  Stmt::Import(ast::StmtImport { names, range: _ }) => {
  if checker.enabled(Rule::MultipleImportsOnOneLine) {

crates/ruff/src/codes.rs

@@ -229,6 +229,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
  (Pylint, "W1510") => (RuleGroup::Unspecified, rules::pylint::rules::SubprocessRunWithoutCheck),
  (Pylint, "W1641") => (RuleGroup::Nursery, rules::pylint::rules::EqWithoutHash),
  (Pylint, "W2901") => (RuleGroup::Unspecified, rules::pylint::rules::RedefinedLoopName),
+ (Pylint, "W3201") => (RuleGroup::Nursery, rules::pylint::rules::BadDunderMethodName),
  (Pylint, "W3301") => (RuleGroup::Unspecified, rules::pylint::rules::NestedMinMax),
 
  // flake8-async

crates/ruff/src/rules/pylint/mod.rs

@@ -130,6 +130,7 @@ mod tests {
  Rule::SubprocessRunWithoutCheck,
  Path::new("subprocess_run_without_check.py")
  )]
+ #[test_case(Rule::BadDunderMethodName, Path::new("bad_dunder_method_name.py"))]
  fn rules(rule_code: Rule, path: &Path) -> Result<()> {
  let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
  let diagnostics = test_path(

crates/ruff/src/rules/pylint/rules/bad_dunder_method_name.rs

@@ -0,0 +1,192 @@
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::identifier::Identifier;
+use ruff_python_ast::Stmt;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for any misspelled dunder name method and for any method
+/// defined with `__...__` that's not one of the pre-defined methods.
+///
+/// The pre-defined methods encompass all of Python's standard dunder
+/// methods.
+///
+/// ## Why is this bad?
+/// Misspelled dunder name methods may cause your code to not function
+/// as expected.
+///
+/// Since dunder methods are associated with customizing the behavior
+/// of a class in Python, introducing a dunder method such as `__foo__`
+/// that diverges from standard Python dunder methods could potentially
+/// confuse someone reading the code.
+///
+/// ## Example
+/// ```python
+/// class Foo:
+/// def __init_(self):
+/// ...
+/// ```
+///
+/// Use instead:
+/// ```python
+/// class Foo:
+/// def __init__(self):
+/// ...
+/// ```
+#[violation]
+pub struct BadDunderMethodName {
+ name: String,
+}
+
+impl Violation for BadDunderMethodName {
+ #[derive_message_formats]
+ fn message(&self) -> String {
+ let BadDunderMethodName { name } = self;
+ format!("Bad or misspelled dunder method name `{name}`. (bad-dunder-name)")
+ }
+}
+
+/// PLW3201
+pub(crate) fn bad_dunder_method_name(checker: &mut Checker, class_body: &[Stmt]) {
+ for method in class_body
+ .iter()
+ .filter_map(ruff_python_ast::Stmt::as_function_def_stmt)
+ .filter(|method| {
+ if is_known_dunder_method(&method.name) {
+ return false;
+ }
+ method.name.starts_with('_') && method.name.ends_with('_')
+ })
+ {
+ checker.diagnostics.push(Diagnostic::new(
+ BadDunderMethodName {
+ name: method.name.to_string(),
+ },
+ method.identifier(),
+ ));
+ }
+}
+
+/// Returns `true` if a method is a known dunder method.
+fn is_known_dunder_method(method: &str) -> bool {
+ matches!(
+ method,
+ "__abs__"
+ | "__add__"
+ | "__aenter__"
+ | "__aexit__"
+ | "__aiter__"
+ | "__and__"
+ | "__anext__"
+ | "__await__"
+ | "__bool__"
+ | "__bytes__"
+ | "__call__"
+ | "__ceil__"
+ | "__class__"
+ | "__class_getitem__"
+ | "__complex__"
+ | "__contains__"
+ | "__copy__"
+ | "__deepcopy__"
+ | "__del__"
+ | "__delattr__"
+ | "__delete__"
+ | "__delitem__"
+ | "__dict__"
+ | "__dir__"
+ | "__divmod__"
+ | "__doc__"
+ | "__enter__"
+ | "__eq__"
+ | "__exit__"
+ | "__float__"
+ | "__floor__"
+ | "__floordiv__"
+ | "__format__"
+ | "__fspath__"
+ | "__ge__"
+ | "__get__"
+ | "__getattr__"
+ | "__getattribute__"
+ | "__getitem__"
+ | "__getnewargs__"
+ | "__getnewargs_ex__"
+ | "__getstate__"
+ | "__gt__"
+ | "__hash__"
+ | "__iadd__"
+ | "__iand__"
+ | "__ifloordiv__"
+ | "__ilshift__"
+ | "__imatmul__"
+ | "__imod__"
+ | "__imul__"
+ | "__init__"
+ | "__init_subclass__"
+ | "__instancecheck__"
+ | "__int__"
+ | "__invert__"
+ | "__ior__"
+ | "__ipow__"
+ | "__irshift__"
+ | "__isub__"
+ | "__iter__"
+ | "__itruediv__"
+ | "__ixor__"
+ | "__le__"
+ | "__len__"
+ | "__length_hint__"
+ | "__lshift__"
+ | "__lt__"
+ | "__matmul__"
+ | "__missing__"
+ | "__mod__"
+ | "__module__"
+ | "__mul__"
+ | "__ne__"
+ | "__neg__"
+ | "__new__"
+ | "__next__"
+ | "__or__"
+ | "__pos__"
+ | "__post_init__"
+ | "__pow__"
+ | "__radd__"
+ | "__rand__"
+ | "__rdivmod__"
+ | "__reduce__"
+ | "__reduce_ex__"
+ | "__repr__"
+ | "__reversed__"
+ | "__rfloordiv__"
+ | "__rlshift__"
+ | "__rmatmul__"
+ | "__rmod__"
+ | "__rmul__"
+ | "__ror__"
+ | "__round__"
+ | "__rpow__"
+ | "__rrshift__"
+ | "__rshift__"
+ | "__rsub__"
+ | "__rtruediv__"
+ | "__rxor__"
+ | "__set__"
+ | "__set_name__"
+ | "__setattr__"
+ | "__setitem__"
+ | "__setstate__"
+ | "__sizeof__"
+ | "__str__"
+ | "__sub__"
+ | "__subclasscheck__"
+ | "__subclasses__"
+ | "__subclasshook__"
+ | "__truediv__"
+ | "__trunc__"
+ | "__weakref__"
+ | "__xor__"
+ )
+}

crates/ruff/src/rules/pylint/rules/mod.rs

@@ -1,5 +1,6 @@
 pub(crate) use assert_on_string_literal::*;
 pub(crate) use await_outside_async::*;
+pub(crate) use bad_dunder_method_name::*;
 pub(crate) use bad_str_strip_call::*;
 pub(crate) use bad_string_format_character::BadStringFormatCharacter;
 pub(crate) use bad_string_format_type::*;
@@ -56,6 +57,7 @@ pub(crate) use yield_in_init::*;
 
 mod assert_on_string_literal;
 mod await_outside_async;
+mod bad_dunder_method_name;
 mod bad_str_strip_call;
 pub(crate) mod bad_string_format_character;
 mod bad_string_format_type;

crates/ruff/src/rules/pylint/snapshots/ruff__rules__pylint__tests__PLW3201_bad_dunder_method_name.py.snap

@@ -0,0 +1,61 @@
+---
+source: crates/ruff/src/rules/pylint/mod.rs
+---
+bad_dunder_method_name.py:2:9: PLW3201 Bad or misspelled dunder method name `_init_`. (bad-dunder-name)
+ |
+1 | class Apples:
+2 | def _init_(self): # [bad-dunder-name]
+ | ^^^^^^ PLW3201
+3 | pass
+ |
+
+bad_dunder_method_name.py:5:9: PLW3201 Bad or misspelled dunder method name `__hello__`. (bad-dunder-name)
+ |
+3 | pass
+4 | 
+5 | def __hello__(self): # [bad-dunder-name]
+ | ^^^^^^^^^ PLW3201
+6 | print("hello")
+ |
+
+bad_dunder_method_name.py:8:9: PLW3201 Bad or misspelled dunder method name `__init_`. (bad-dunder-name)
+ |
+ 6 | print("hello")
+ 7 | 
+ 8 | def __init_(self): # [bad-dunder-name]
+ | ^^^^^^^ PLW3201
+ 9 | # author likely unintentionally misspelled the correct init dunder.
+10 | pass
+ |
+
+bad_dunder_method_name.py:12:9: PLW3201 Bad or misspelled dunder method name `_init_`. (bad-dunder-name)
+ |
+10 | pass
+11 | 
+12 | def _init_(self): # [bad-dunder-name]
+ | ^^^^^^ PLW3201
+13 | # author likely unintentionally misspelled the correct init dunder.
+14 | pass
+ |
+
+bad_dunder_method_name.py:16:9: PLW3201 Bad or misspelled dunder method name `___neg__`. (bad-dunder-name)
+ |
+14 | pass
+15 | 
+16 | def ___neg__(self): # [bad-dunder-name]
+ | ^^^^^^^^ PLW3201
+17 | # author likely accidentally added an additional `_`
+18 | pass
+ |
+
+bad_dunder_method_name.py:20:9: PLW3201 Bad or misspelled dunder method name `__inv__`. (bad-dunder-name)
+ |
+18 | pass
+19 | 
+20 | def __inv__(self): # [bad-dunder-name]
+ | ^^^^^^^ PLW3201
+21 | # author likely meant to call the invert dunder method
+22 | pass
+ |
+
+