Fix a false positive with singledispatchmethod-function (#9599)

* Fix a false positive with ``singledispatchmethod-function`` when a method is decorated with both ``functools.singledispatchmethod`` and ``staticmethod``.

Closes #9531

doc/data/messages/s/singledispatch-method/bad.py

@@ -3,17 +3,14 @@
 
 class Board:
     @singledispatch  # [singledispatch-method]
-    @classmethod
-    def convert_position(cls, position):
+    def convert_position(self, position):
         pass
 
     @convert_position.register  # [singledispatch-method]
-    @classmethod
-    def _(cls, position: str) -> tuple:
+    def _(self, position: str) -> tuple:
         position_a, position_b = position.split(",")
         return (int(position_a), int(position_b))
 
     @convert_position.register  # [singledispatch-method]
-    @classmethod
-    def _(cls, position: tuple) -> str:
+    def _(self, position: tuple) -> str:
         return f"{position[0]},{position[1]}"

doc/data/messages/s/singledispatch-method/good.py

@@ -1,19 +1,17 @@
 from functools import singledispatch
 
 
-class Board:
-    @singledispatch
-    @staticmethod
-    def convert_position(position):
-        pass
+@singledispatch
+def convert_position(position):
+    print(position)
 
-    @convert_position.register
-    @staticmethod
-    def _(position: str) -> tuple:
-        position_a, position_b = position.split(",")
-        return (int(position_a), int(position_b))
 
-    @convert_position.register
-    @staticmethod
-    def _(position: tuple) -> str:
-        return f"{position[0]},{position[1]}"
+@convert_position.register
+def _(position: str) -> tuple:
+    position_a, position_b = position.split(",")
+    return (int(position_a), int(position_b))
+
+
+@convert_position.register
+def _(position: tuple) -> str:
+    return f"{position[0]},{position[1]}"

doc/data/messages/s/singledispatchmethod-function/bad.py

@@ -1,19 +1,17 @@
 from functools import singledispatchmethod
 
 
-class Board:
-    @singledispatchmethod  # [singledispatchmethod-function]
-    @staticmethod
-    def convert_position(position):
-        pass
+@singledispatchmethod  # [singledispatchmethod-function]
+def convert_position(position):
+    print(position)
 
-    @convert_position.register  # [singledispatchmethod-function]
-    @staticmethod
-    def _(position: str) -> tuple:
-        position_a, position_b = position.split(",")
-        return (int(position_a), int(position_b))
 
-    @convert_position.register  # [singledispatchmethod-function]
-    @staticmethod
-    def _(position: tuple) -> str:
-        return f"{position[0]},{position[1]}"
+@convert_position.register  # [singledispatchmethod-function]
+def _(position: str) -> tuple:
+    position_a, position_b = position.split(",")
+    return (int(position_a), int(position_b))
+
+
+@convert_position.register  # [singledispatchmethod-function]
+def _(position: tuple) -> str:
+    return f"{position[0]},{position[1]}"

doc/whatsnew/fragments/9531.false_positive

@@ -0,0 +1,3 @@
+Fix a false positive with ``singledispatchmethod-function`` when a method is decorated with both ``functools.singledispatchmethod`` and ``staticmethod``.
+
+Closes #9531

pylint/checkers/stdlib.py

@@ -673,8 +673,9 @@ def visit_boolop(self, node: nodes.BoolOp) -> None:
         "singledispatchmethod-function",
     )
     def visit_functiondef(self, node: nodes.FunctionDef) -> None:
-        if node.decorators and isinstance(node.parent, nodes.ClassDef):
-            self._check_lru_cache_decorators(node)
+        if node.decorators:
+            if isinstance(node.parent, nodes.ClassDef):
+                self._check_lru_cache_decorators(node)
             self._check_dispatch_decorators(node)
 
     def _check_lru_cache_decorators(self, node: nodes.FunctionDef) -> None:
@@ -733,16 +734,14 @@ def _check_dispatch_decorators(self, node: nodes.FunctionDef) -> None:
                     interfaces.INFERENCE,
                 )
 
-        if "singledispatch" in decorators_map and "classmethod" in decorators_map:
-            self.add_message(
-                "singledispatch-method",
-                node=decorators_map["singledispatch"][0],
-                confidence=decorators_map["singledispatch"][1],
-            )
-        elif (
-            "singledispatchmethod" in decorators_map
-            and "staticmethod" in decorators_map
-        ):
+        if node.is_method():
+            if "singledispatch" in decorators_map:
+                self.add_message(
+                    "singledispatch-method",
+                    node=decorators_map["singledispatch"][0],
+                    confidence=decorators_map["singledispatch"][1],
+                )
+        elif "singledispatchmethod" in decorators_map:
             self.add_message(
                 "singledispatchmethod-function",
                 node=decorators_map["singledispatchmethod"][0],

tests/functional/s/singledispatch/singledispatch_method.py

@@ -0,0 +1,72 @@
+"""Tests for singledispatch-method"""
+# pylint: disable=missing-class-docstring, missing-function-docstring,too-few-public-methods
+
+
+from functools import singledispatch
+
+
+class Board1:
+    @singledispatch  # [singledispatch-method]
+    def convert_position(self, position):
+        pass
+
+    @convert_position.register  # [singledispatch-method]
+    def _(self, position: str) -> tuple:
+        position_a, position_b = position.split(",")
+        return (int(position_a), int(position_b))
+
+    @convert_position.register  # [singledispatch-method]
+    def _(self, position: tuple) -> str:
+        return f"{position[0]},{position[1]}"
+
+
+class Board2:
+    @singledispatch  # [singledispatch-method]
+    @classmethod
+    def convert_position(cls, position):
+        pass
+
+    @convert_position.register  # [singledispatch-method]
+    @classmethod
+    def _(cls, position: str) -> tuple:
+        position_a, position_b = position.split(",")
+        return (int(position_a), int(position_b))
+
+    @convert_position.register  # [singledispatch-method]
+    @classmethod
+    def _(cls, position: tuple) -> str:
+        return f"{position[0]},{position[1]}"
+
+
+
+class Board3:
+    @singledispatch  # [singledispatch-method]
+    @staticmethod
+    def convert_position(position):
+        pass
+
+    @convert_position.register  # [singledispatch-method]
+    @staticmethod
+    def _(position: str) -> tuple:
+        position_a, position_b = position.split(",")
+        return (int(position_a), int(position_b))
+
+    @convert_position.register  # [singledispatch-method]
+    @staticmethod
+    def _(position: tuple) -> str:
+        return f"{position[0]},{position[1]}"
+
+
+# Do not emit `singledispatch-method`:
+@singledispatch
+def convert_position(position):
+    print(position)
+
+@convert_position.register
+def _(position: str) -> tuple:
+    position_a, position_b = position.split(",")
+    return (int(position_a), int(position_b))
+
+@convert_position.register
+def _(position: tuple) -> str:
+    return f"{position[0]},{position[1]}"

tests/functional/s/singledispatch/singledispatch_method.txt

@@ -1,3 +1,9 @@
-singledispatch-method:26:5:26:19:Board.convert_position:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:HIGH
-singledispatch-method:31:5:31:30:Board._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
-singledispatch-method:37:5:37:30:Board._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
+singledispatch-method:9:5:9:19:Board1.convert_position:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:HIGH
+singledispatch-method:13:5:13:30:Board1._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
+singledispatch-method:18:5:18:30:Board1._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
+singledispatch-method:24:5:24:19:Board2.convert_position:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:HIGH
+singledispatch-method:29:5:29:30:Board2._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
+singledispatch-method:35:5:35:30:Board2._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
+singledispatch-method:43:5:43:19:Board3.convert_position:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:HIGH
+singledispatch-method:48:5:48:30:Board3._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE
+singledispatch-method:54:5:54:30:Board3._:singledispatch decorator should not be used with methods, use singledispatchmethod instead.:INFERENCE

tests/functional/s/singledispatch/singledispatchmethod_function.py

@@ -0,0 +1,71 @@
+"""Tests for singledispatchmethod-function"""
+# pylint: disable=missing-class-docstring, missing-function-docstring,too-few-public-methods
+
+
+from functools import singledispatchmethod
+
+
+# Emit `singledispatchmethod-function` when functions are decorated with `singledispatchmethod`
+@singledispatchmethod  # [singledispatchmethod-function]
+def convert_position2(position):
+    print(position)
+
+@convert_position2.register  # [singledispatchmethod-function]
+def _(position: str) -> tuple:
+    position_a, position_b = position.split(",")
+    return (int(position_a), int(position_b))
+
+@convert_position2.register  # [singledispatchmethod-function]
+def _(position: tuple) -> str:
+    return f"{position[0]},{position[1]}"
+
+
+class Board1:
+    @singledispatchmethod
+    def convert_position(self, position):
+        pass
+
+    @convert_position.register
+    def _(self, position: str) -> tuple:
+        position_a, position_b = position.split(",")
+        return (int(position_a), int(position_b))
+
+    @convert_position.register
+    def _(self, position: tuple) -> str:
+        return f"{position[0]},{position[1]}"
+
+
+class Board2:
+    @singledispatchmethod
+    @staticmethod
+    def convert_position(position):
+        pass
+
+    @convert_position.register
+    @staticmethod
+    def _(position: str) -> tuple:
+        position_a, position_b = position.split(",")
+        return (int(position_a), int(position_b))
+
+    @convert_position.register
+    @staticmethod
+    def _(position: tuple) -> str:
+        return f"{position[0]},{position[1]}"
+
+
+class Board3:
+    @singledispatchmethod
+    @classmethod
+    def convert_position(cls, position):
+        pass
+
+    @convert_position.register
+    @classmethod
+    def _(cls, position: str) -> tuple:
+        position_a, position_b = position.split(",")
+        return (int(position_a), int(position_b))
+
+    @convert_position.register
+    @classmethod
+    def _(cls, position: tuple) -> str:
+        return f"{position[0]},{position[1]}"

tests/functional/s/singledispatch/singledispatchmethod_function.txt

@@ -0,0 +1,3 @@
+singledispatchmethod-function:9:1:9:21:convert_position2:singledispatchmethod decorator should not be used with functions, use singledispatch instead.:HIGH
+singledispatchmethod-function:13:1:13:27:_:singledispatchmethod decorator should not be used with functions, use singledispatch instead.:INFERENCE
+singledispatchmethod-function:18:1:18:27:_:singledispatchmethod decorator should not be used with functions, use singledispatch instead.:INFERENCE