[pylint] Don't recommend decorating staticmethods with @singledispatch (PLE1519, PLE1520) (#10637)

Co-authored-by: Alex Waygood <alex.waygood@gmail.com>

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

@@ -20,7 +20,7 @@ class Board:
     def place(self, position):
         pass
 
-    @singledispatch
+    @singledispatch  # [singledispatch-method]
     @staticmethod
     def do(position):
         pass

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

@@ -17,7 +17,7 @@ class Board:
     def move(self, position):
         pass
 
-    @singledispatchmethod  # [singledispatchmethod-function]
+    @singledispatchmethod  # Ok
     @staticmethod
     def do(position):
         pass

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

@@ -9,13 +9,13 @@ use crate::checkers::ast::Checker;
 use crate::importer::ImportRequest;
 
 /// ## What it does
-/// Checks for `@singledispatch` decorators on class and instance methods.
+/// Checks for methods decorated with `@singledispatch`.
 ///
 /// ## Why is this bad?
 /// The `@singledispatch` decorator is intended for use with functions, not methods.
 ///
 /// Instead, use the `@singledispatchmethod` decorator, or migrate the method to a
-/// standalone function or `@staticmethod`.
+/// standalone function.
 ///
 /// ## Example
 /// ```python
@@ -88,7 +88,9 @@ pub(crate) fn singledispatch_method(
     );
     if !matches!(
         type_,
-        function_type::FunctionType::Method | function_type::FunctionType::ClassMethod
+        function_type::FunctionType::Method
+            | function_type::FunctionType::ClassMethod
+            | function_type::FunctionType::StaticMethod
     ) {
         return;
     }

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

@@ -9,12 +9,11 @@ use crate::checkers::ast::Checker;
 use crate::importer::ImportRequest;
 
 /// ## What it does
-/// Checks for `@singledispatchmethod` decorators on functions or static
+/// Checks for non-method functions decorated with `@singledispatchmethod`.
-/// methods.
 ///
 /// ## Why is this bad?
-/// The `@singledispatchmethod` decorator is intended for use with class and
+/// The `@singledispatchmethod` decorator is intended for use with methods, not
-/// instance methods, not functions.
+/// functions.
 ///
 /// Instead, use the `@singledispatch` decorator.
 ///
@@ -85,10 +84,7 @@ pub(crate) fn singledispatchmethod_function(
         &checker.settings.pep8_naming.classmethod_decorators,
         &checker.settings.pep8_naming.staticmethod_decorators,
     );
-    if !matches!(
+    if !matches!(type_, function_type::FunctionType::Function) {
-        type_,
-        function_type::FunctionType::Function | function_type::FunctionType::StaticMethod
-    ) {
         return;
     }
 

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLE1519_singledispatch_method.py.snap

@@ -41,3 +41,24 @@ singledispatch_method.py:15:5: PLE1519 [*] `@singledispatch` decorator should no
 16 16 |     def move(self, position):
 17 17 |         pass
 18 18 | 
+
+singledispatch_method.py:23:5: PLE1519 [*] `@singledispatch` decorator should not be used on methods
+   |
+21 |         pass
+22 | 
+23 |     @singledispatch  # [singledispatch-method]
+   |     ^^^^^^^^^^^^^^^ PLE1519
+24 |     @staticmethod
+25 |     def do(position):
+   |
+   = help: Replace with `@singledispatchmethod`
+
+ℹ Unsafe fix
+20 20 |     def place(self, position):
+21 21 |         pass
+22 22 | 
+23    |-    @singledispatch  # [singledispatch-method]
+   23 |+    @singledispatchmethod  # [singledispatch-method]
+24 24 |     @staticmethod
+25 25 |     def do(position):
+26 26 |         pass

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLE1520_singledispatchmethod_function.py.snap

@@ -20,30 +20,3 @@ singledispatchmethod_function.py:4:1: PLE1520 [*] `@singledispatchmethod` decora
 5 5 | def convert_position(position):
 6 6 |     pass
 7 7 |
-
-singledispatchmethod_function.py:20:5: PLE1520 [*] `@singledispatchmethod` decorator should not be used on non-method functions
-   |
-18 |         pass
-19 | 
-20 |     @singledispatchmethod  # [singledispatchmethod-function]
-   |     ^^^^^^^^^^^^^^^^^^^^^ PLE1520
-21 |     @staticmethod
-22 |     def do(position):
-   |
-   = help: Replace with `@singledispatch`
-
-ℹ Unsafe fix
-1     |-from functools import singledispatchmethod
-   1  |+from functools import singledispatchmethod, singledispatch
-2  2  | 
-3  3  | 
-4  4  | @singledispatchmethod  # [singledispatchmethod-function]
---------------------------------------------------------------------------------
-17 17 |     def move(self, position):
-18 18 |         pass
-19 19 | 
-20    |-    @singledispatchmethod  # [singledispatchmethod-function]
-   20 |+    @singledispatch  # [singledispatchmethod-function]
-21 21 |     @staticmethod
-22 22 |     def do(position):
-23 23 |         pass