Fix unsubscriptable-object for generic classes (PEP 695)

Author: cdce8p

ChangeLog

@@ -22,6 +22,10 @@ Release date: TBA
   Refs pylint-dev/#9626
   Refs pylint-dev/#9623
 
+* Fix ``unsubscriptable-object`` error for generic classes using the PEP 695 syntax (Python 3.12).
+
+  Closes pylint-dev/#9406
+
 
 What's New in astroid 3.2.1?
 ============================

astroid/brain/brain_typing.py

@@ -196,6 +196,28 @@ def infer_typing_attr(
     return node.infer(context=ctx)
 
 
+def _looks_like_generic_class_pep695(node: ClassDef) -> bool:
+    """Check if class is uses type parameter. Python 3.12+."""
+    return len(node.type_params) > 0
+
+
+def infer_typing_generic_class_pep695(
+    node: ClassDef, ctx: context.InferenceContext | None = None
+) -> Iterator[ClassDef]:
+    """Add __class_getitem__ for generic classes. Python 3.12+."""
+    try:
+        value = next(node.infer())
+    except (InferenceError, StopIteration) as exc:
+        raise UseInferenceDefault from exc
+
+    if not (isinstance(value, ClassDef) and value.type_params):
+        raise UseInferenceDefault
+
+    func_to_add = _extract_single_node(CLASS_GETITEM_TEMPLATE)
+    value.locals["__class_getitem__"] = [func_to_add]
+    return iter([value])
+
+
 def _looks_like_typedDict(  # pylint: disable=invalid-name
     node: FunctionDef | ClassDef,
 ) -> bool:
@@ -490,3 +512,8 @@ def register(manager: AstroidManager) -> None:
 
     if PY312_PLUS:
         register_module_extender(manager, "typing", _typing_transform)
+        manager.register_transform(
+            ClassDef,
+            inference_tip(infer_typing_generic_class_pep695),
+            _looks_like_generic_class_pep695,
+        )

tests/brain/test_brain.py

@@ -627,6 +627,18 @@ def test_typing_generic_subscriptable(self):
         assert isinstance(inferred, nodes.ClassDef)
         assert isinstance(inferred.getattr("__class_getitem__")[0], nodes.FunctionDef)
 
+    @test_utils.require_version(minver="3.12")
+    def test_typing_generic_subscriptable_pep695(self):
+        """Test class using type parameters is subscriptable with __class_getitem__ (added in PY312)"""
+        node = builder.extract_node(
+            """
+        class Foo[T]: ...
+        """
+        )
+        inferred = next(node.infer())
+        assert isinstance(inferred, nodes.ClassDef)
+        assert isinstance(inferred.getattr("__class_getitem__")[0], nodes.FunctionDef)
+
     @test_utils.require_version(minver="3.9")
     def test_typing_annotated_subscriptable(self):
         """Test typing.Annotated is subscriptable with __class_getitem__"""