Fix Python 3.12 generic type syntax (#10135)

Author: marzukr

doc/whatsnew/fragments/9335.false_positive

@@ -0,0 +1,4 @@
+Fix false positives for ``undefined-variable`` for classes using Python 3.12
+generic type syntax.
+
+Closes #9335

pylint/checkers/variables.py

@@ -1742,6 +1742,11 @@ def _should_node_be_skipped(
             if utils.is_ancestor_name(consumer.node, node) or (
                 not is_start_index and self._ignore_class_scope(node)
             ):
+                if any(
+                    node.name == param.name.name for param in consumer.node.type_params
+                ):
+                    return False
+
                 return True
 
             # Ignore inner class scope for keywords in class definition
@@ -1952,7 +1957,9 @@ def _check_consumer(
                 )
             return (VariableVisitConsumerAction.RETURN, found_nodes)
 
-        elif isinstance(defstmt, nodes.ClassDef):
+        elif (
+            isinstance(defstmt, nodes.ClassDef) and defnode not in defframe.type_params
+        ):
             return self._is_first_level_self_reference(node, defstmt, found_nodes)
 
         elif isinstance(defnode, nodes.NamedExpr):
@@ -2334,6 +2341,13 @@ def _is_variable_violation(
                     maybe_before_assign = defnode.value is node or any(
                         anc is defnode.value for anc in node.node_ancestors()
                     )
+                elif (
+                    isinstance(defframe, nodes.ClassDef)
+                    and defnode in defframe.type_params
+                ):
+                    # Generic on parent class:
+                    # class Child[_T](Parent[_T])
+                    maybe_before_assign = False
 
         return maybe_before_assign, annotation_return, use_outer_definition
 

tests/functional/g/generic_class_syntax_py312.py

@@ -2,7 +2,7 @@
 class Entity[_T: float]:
     last_update: int | None = None
 
-    def __init__(self, data: _T) -> None:  # [undefined-variable]  # false-positive
+    def __init__(self, data: _T) -> None:
         self.data = data
 
 
@@ -28,6 +28,6 @@ def __init__(self):
         self.update_interval = 0
 
 
-class Child[_T](Parent[_T]):  # [undefined-variable]  # false-positive
+class Child[_T](Parent[_T]):
     def func(self):
         self.update_interval = None

tests/functional/g/generic_class_syntax_py312.txt

@@ -4,4 +4,5 @@ def f[T](a: T) -> T:
     print(a)
 
 class ChildClass[T, *Ts, **P]:
-    ...
+    def __init__(self, value: T):
+        self.value = value