class attrs should not emit assigning-non-slot msg (#7987)

doc/whatsnew/fragments/6001.false_positive

@@ -0,0 +1,3 @@
+Fix false positive ``assigning-non-slot`` when a class attribute is re-assigned.
+
+Closes #6001

pylint/checkers/classes/class_checker.py

@@ -1630,6 +1630,10 @@ def _check_in_slots(self, node: nodes.AssignAttr) -> None:
                     # Properties circumvent the slots mechanism,
                     # so we should not emit a warning for them.
                     return
+                if node.attrname != "__class__" and utils.is_class_attr(
+                    node.attrname, klass
+                ):
+                    return
                 if node.attrname in klass.locals:
                     for local_name in klass.locals.get(node.attrname):
                         statement = local_name.statement(future=True)
@@ -1645,7 +1649,12 @@ def _check_in_slots(self, node: nodes.AssignAttr) -> None:
                     slots, node.parent.value
                 ):
                     return
-                self.add_message("assigning-non-slot", args=(node.attrname,), node=node)
+                self.add_message(
+                    "assigning-non-slot",
+                    args=(node.attrname,),
+                    node=node,
+                    confidence=INFERENCE,
+                )
 
     @only_required_for_messages(
         "protected-access", "no-classmethod-decorator", "no-staticmethod-decorator"
@@ -1780,7 +1789,7 @@ def _check_protected_attribute_access(
                 if (
                     self._is_classmethod(node.frame(future=True))
                     and self._is_inferred_instance(node.expr, klass)
-                    and self._is_class_attribute(attrname, klass)
+                    and self._is_class_or_instance_attribute(attrname, klass)
                 ):
                     return
 
@@ -1827,19 +1836,16 @@ def _is_inferred_instance(expr: nodes.NodeNG, klass: nodes.ClassDef) -> bool:
         return inferred._proxied is klass
 
     @staticmethod
-    def _is_class_attribute(name: str, klass: nodes.ClassDef) -> bool:
+    def _is_class_or_instance_attribute(name: str, klass: nodes.ClassDef) -> bool:
         """Check if the given attribute *name* is a class or instance member of the
         given *klass*.
 
         Returns ``True`` if the name is a property in the given klass,
         ``False`` otherwise.
         """
 
-        try:
-            klass.getattr(name)
+        if utils.is_class_attr(name, klass):
             return True
-        except astroid.NotFoundError:
-            pass
 
         try:
             klass.instance_attr(name)

pylint/checkers/utils.py

@@ -2190,3 +2190,11 @@ def is_terminating_func(node: nodes.Call) -> bool:
         pass
 
     return False
+
+
+def is_class_attr(name: str, klass: nodes.ClassDef) -> bool:
+    try:
+        klass.getattr(name)
+        return True
+    except astroid.NotFoundError:
+        return False

tests/functional/a/assigning/assigning_non_slot.py

@@ -2,6 +2,8 @@
 will trigger assigning-non-slot warning.
 """
 # pylint: disable=too-few-public-methods, missing-docstring, import-error, redundant-u-string-prefix, unnecessary-dunder-call
+# pylint: disable=attribute-defined-outside-init
+
 from collections import deque
 
 from missing import Unknown
@@ -129,7 +131,7 @@ def dont_emit_for_descriptors():
     # This should not emit, because attr is
     # a data descriptor
     inst.data_descriptor = 'foo'
-    inst.non_data_descriptor = 'lala' # [assigning-non-slot]
+    inst.non_data_descriptor = 'lala'
 
 
 class ClassWithSlots:
@@ -147,7 +149,8 @@ class ClassReassingingInvalidLayoutClass:
     __slots__ = []
 
     def release(self):
-        self.__class__ = ClassWithSlots # [assigning-non-slot]
+        self.__class__ = ClassWithSlots  # [assigning-non-slot]
+        self.test = 'test'  # [assigning-non-slot]
 
 
 # pylint: disable=attribute-defined-outside-init
@@ -200,3 +203,39 @@ def dont_emit_for_defined_setattr():
 
     child = ClassWithParentDefiningSetattr()
     child.non_existent = "non-existent"
+
+class ColorCls:
+    __slots__ = ()
+    COLOR = "red"
+
+
+class Child(ColorCls):
+    __slots__ = ()
+
+
+repro = Child()
+Child.COLOR = "blue"
+
+class MyDescriptor:
+    """Basic descriptor."""
+
+    def __get__(self, instance, owner):
+        return 42
+
+    def __set__(self, instance, value):
+        pass
+
+
+# Regression test from https://github.com/PyCQA/pylint/issues/6001
+class Base:
+    __slots__ = ()
+
+    attr2 = MyDescriptor()
+
+
+class Repro(Base):
+    __slots__ = ()
+
+
+repro = Repro()
+repro.attr2 = "anything"

tests/functional/a/assigning/assigning_non_slot.txt

@@ -1,5 +1,5 @@
-assigning-non-slot:18:8:18:20:Bad.__init__:Assigning to attribute 'missing' not defined in class slots:UNDEFINED
-assigning-non-slot:26:8:26:20:Bad2.__init__:Assigning to attribute 'missing' not defined in class slots:UNDEFINED
-assigning-non-slot:36:8:36:20:Bad3.__init__:Assigning to attribute 'missing' not defined in class slots:UNDEFINED
-assigning-non-slot:132:4:132:28:dont_emit_for_descriptors:Assigning to attribute 'non_data_descriptor' not defined in class slots:UNDEFINED
-assigning-non-slot:150:8:150:22:ClassReassingingInvalidLayoutClass.release:Assigning to attribute '__class__' not defined in class slots:UNDEFINED
+assigning-non-slot:20:8:20:20:Bad.__init__:Assigning to attribute 'missing' not defined in class slots:INFERENCE
+assigning-non-slot:28:8:28:20:Bad2.__init__:Assigning to attribute 'missing' not defined in class slots:INFERENCE
+assigning-non-slot:38:8:38:20:Bad3.__init__:Assigning to attribute 'missing' not defined in class slots:INFERENCE
+assigning-non-slot:152:8:152:22:ClassReassingingInvalidLayoutClass.release:Assigning to attribute '__class__' not defined in class slots:INFERENCE
+assigning-non-slot:153:8:153:17:ClassReassingingInvalidLayoutClass.release:Assigning to attribute 'test' not defined in class slots:INFERENCE

tests/functional/a/assigning/assigning_non_slot_4509.txt

@@ -1 +1 @@
-assigning-non-slot:18:8:18:17:Foo.__init__:Assigning to attribute '_bar' not defined in class slots:UNDEFINED
+assigning-non-slot:18:8:18:17:Foo.__init__:Assigning to attribute '_bar' not defined in class slots:INFERENCE