[pylint] removed dunder methods in Python 3 (PLW3201)

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

@@ -94,6 +94,9 @@ def __prepare__():
     def __mro_entries__(self, bases):
         pass
 
+    # Deprecated in Python 3
+    def __unicode__(self):
+        pass
 
 def __foo_bar__():  # this is not checked by the [bad-dunder-name] rule
     ...

crates/ruff_linter/src/rules/pylint/helpers.rs

@@ -168,10 +168,16 @@ impl<'a> Visitor<'_> for SequenceIndexVisitor<'a> {
     }
 }
 
-/// Returns `true` if a method is a known dunder method.
-pub(super) fn is_known_dunder_method(method: &str) -> bool {
-    matches!(
-        method,
+/// The kind of dunder method.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub(super) enum DunderMethodKind {
+    Known,
+    Removed,
+}
+
+/// Returns the kind of dunder method.
+pub(super) fn dunder_method_kind(method: &str) -> Option<DunderMethodKind> {
+    match method {
         "__abs__"
             | "__add__"
             | "__aenter__"
@@ -304,6 +310,29 @@ pub(super) fn is_known_dunder_method(method: &str) -> bool {
             | "_missing_"
             | "_ignore_"
             | "_order_"
-            | "_generate_next_value_"
-    )
+            | "_generate_next_value_" => Some(DunderMethodKind::Known),
+        "__unicode__"
+            | "__div__"
+            | "__rdiv__"
+            | "__idiv__"
+            | "__nonzero__"
+            | "__metaclass__"
+            | "__cmp__"
+            | "__getslice__"
+            | "__setslice__"
+            | "__delslice__"
+            | "__oct__"
+            | "__hex__"
+            | "__members__"
+            | "__method__"
+            | "__coerce__"
+            | "__long__"
+            | "__rcmp__" => Some(DunderMethodKind::Removed),
+            _ => None,
+        }
+}
+
+/// Returns `true` if a method is a known dunder method.
+pub(super) fn is_known_dunder_method(method: &str) -> bool {
+    dunder_method_kind(method) == Some(DunderMethodKind::Known)
 }

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

@@ -5,13 +5,19 @@ use ruff_python_ast::identifier::Identifier;
 use ruff_python_semantic::analyze::visibility;
 
 use crate::checkers::ast::Checker;
-use crate::rules::pylint::helpers::is_known_dunder_method;
+use crate::rules::pylint::helpers::{dunder_method_kind, DunderMethodKind};
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+enum Kind {
+    Misspelled,
+    RemovedInPython3,
+}
 
 /// ## What it does
-/// Checks for misspelled and unknown dunder names in method definitions.
+/// Checks for misspelled, unknown and no longer supported dunder names in method definitions.
 ///
 /// ## Why is this bad?
-/// Misspelled dunder name methods may cause your code to not function
+/// Misspelled or no longer supported dunder name methods may cause your code to not function
 /// as expected.
 ///
 /// Since dunder methods are associated with customizing the behavior
@@ -45,13 +51,19 @@ use crate::rules::pylint::helpers::is_known_dunder_method;
 #[violation]
 pub struct BadDunderMethodName {
     name: String,
+    kind: Kind,
 }
 
 impl Violation for BadDunderMethodName {
     #[derive_message_formats]
     fn message(&self) -> String {
-        let BadDunderMethodName { name } = self;
-        format!("Bad or misspelled dunder method name `{name}`")
+        let BadDunderMethodName { name, kind } = self;
+        match kind {
+            Kind::Misspelled => format!("Bad or misspelled dunder method name `{name}`"),
+            Kind::RemovedInPython3 => {
+                format!("Python 2 or older only dunder method name `{name}`")
+            }
+        }
     }
 }
 
@@ -63,12 +75,11 @@ pub(crate) fn bad_dunder_method_name(checker: &mut Checker, method: &ast::StmtFu
     }
 
     // If the name is explicitly allowed, skip it.
-    if is_known_dunder_method(&method.name)
-        || checker
-            .settings
-            .pylint
-            .allow_dunder_method_names
-            .contains(method.name.as_str())
+    if checker
+        .settings
+        .pylint
+        .allow_dunder_method_names
+        .contains(method.name.as_str())
         || matches!(method.name.as_str(), "_")
     {
         return;
@@ -78,9 +89,17 @@ pub(crate) fn bad_dunder_method_name(checker: &mut Checker, method: &ast::StmtFu
         return;
     }
 
+    // If the method is known, skip it.
+    let kind = match dunder_method_kind(&method.name) {
+        Some(DunderMethodKind::Known) => return,
+        Some(DunderMethodKind::Removed) => Kind::RemovedInPython3,
+        None => Kind::Misspelled,
+    };
+
     checker.diagnostics.push(Diagnostic::new(
         BadDunderMethodName {
             name: method.name.to_string(),
+            kind,
         },
         method.identifier(),
     ));

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLW3201_bad_dunder_method_name.py.snap

@@ -58,4 +58,10 @@ bad_dunder_method_name.py:23:9: PLW3201 Bad or misspelled dunder method name `__
 25 |         pass
    |
 
-
+bad_dunder_method_name.py:98:9: PLW3201 Python 2 or older only dunder method name `__unicode__`
+   |
+97 |     # Deprecated in Python 3
+98 |     def __unicode__(self):
+   |         ^^^^^^^^^^^ PLW3201
+99 |         pass
+   |