Fix issue with slots caching

astroid/brain/brain_typing.py

@@ -160,6 +160,16 @@ def infer_typing_attr(
         # infer the native methods, replace them for an easy inference tip
         func_to_add = astroid.extract_node(CLASS_GETITEM_TEMPLATE)
         value.locals["__class_getitem__"] = [func_to_add]
+        if (
+            isinstance(node.parent, nodes.ClassDef)
+            and node in node.parent.bases
+            and getattr(node.parent, "__cache", None)
+        ):
+            # node.parent.slots is evaluated and cached before the inference tip
+            # is first applied. Remove the last result to allow a recalculation of slots
+            cache = getattr(node.parent, "__cache")
+            if cache and cache.get(node.parent.slots) is not None:
+                del cache[node.parent.slots]
         return iter([value])
 
     node = extract_node(TYPING_TYPE_TEMPLATE.format(value.qname().split(".")[-1]))

tests/unittest_brain.py

@@ -1388,6 +1388,29 @@ def test_typing_annotated_subscriptable(self):
         assert isinstance(inferred, nodes.ClassDef)
         assert isinstance(inferred.getattr("__class_getitem__")[0], nodes.FunctionDef)
 
+    @test_utils.require_version(minver="3.7")
+    def test_typing_generic_slots(self):
+        """Test cache reset for slots if Generic subscript is inferred."""
+        node = builder.extract_node(
+            """
+        from typing import Generic, TypeVar
+        T = TypeVar('T')
+        class A(Generic[T]):
+            __slots__ = ['value']
+            def __init__(self, value):
+                self.value = value
+        """
+        )
+        inferred = next(node.infer())
+        assert len(inferred.slots()) == 0
+        # Only after the subscript base is inferred and the inference tip applied,
+        # will slots contain the correct value
+        next(node.bases[0].infer())
+        slots = inferred.slots()
+        assert len(slots) == 1
+        assert isinstance(slots[0], nodes.Const)
+        assert slots[0].value == "value"
+
     def test_has_dunder_args(self):
         ast_node = builder.extract_node(
             """