Raise a better error when a generic alias is used inside type[] (#11088)

Viicos · web-flow · commit c393317161f3 · 2024-12-13T11:06:23.000+01:00
diff --git a/pydantic/_internal/_generate_schema.py b/pydantic/_internal/_generate_schema.py
@@ -63,7 +63,7 @@
 from ..json_schema import JsonSchemaValue
 from ..version import version_short
 from ..warnings import PydanticDeprecatedSince20
-from . import _core_utils, _decorators, _discriminated_union, _known_annotated_metadata, _typing_extra
+from . import _core_utils, _decorators, _discriminated_union, _known_annotated_metadata, _repr, _typing_extra
 from ._config import ConfigWrapper, ConfigWrapperStack
 from ._core_metadata import update_core_metadata
 from ._core_utils import (
@@ -1647,7 +1647,12 @@ def _subclass_schema(self, type_: Any) -> core_schema.CoreSchema:
         else:
             if _typing_extra.is_self(type_param):
                 type_param = self._resolve_self_type(type_param)
-
+            if _typing_extra.is_generic_alias(type_param):
+                raise PydanticUserError(
+                    'Subscripting `type[]` with an already parametrized type is not supported. '
+                    f'Instead of using type[{type_param!r}], use type[{_repr.display_as_type(get_origin(type_param))}].',
+                    code=None,
+                )
             if not inspect.isclass(type_param):
                 raise TypeError(f'Expected a class, got {type_param!r}')
             return core_schema.is_subclass_schema(type_param)
diff --git a/tests/test_edge_cases.py b/tests/test_edge_cases.py
@@ -35,6 +35,7 @@
     PrivateAttr,
     PydanticDeprecatedSince20,
     PydanticSchemaGenerationError,
+    PydanticUserError,
     RootModel,
     TypeAdapter,
     ValidationError,
@@ -1470,6 +1471,17 @@ class Model(BaseModel):
     ]
 
 
+def test_type_on_generic_alias() -> None:
+    error_msg = 'Instead of using type[typing.List[int]], use type[list].'
+
+    with pytest.raises(PydanticUserError) as exc_info:
+
+        class Model(BaseModel):
+            a: Type[List[int]]
+
+    assert error_msg in exc_info.value.message
+
+
 def test_type_assign():
     class Parent:
         def echo(self):
