Fix issue with recursion error caused by ParamSpec (#6923)

pydantic/_internal/_generics.py

@@ -359,7 +359,7 @@ def has_instance_in_type(type_: Any, isinstance_target: Any) -> bool:
 
     # Handle special case for typehints that can have lists as arguments.
     # `typing.Callable[[int, str], int]` is an example for this.
-    if isinstance(type_, (List, list)):
+    if isinstance(type_, (List, list)) and not isinstance(type_, typing_extensions.ParamSpec):
         if any(has_instance_in_type(element, isinstance_target) for element in type_):
             return True
 

tests/test_generics.py

@@ -32,7 +32,7 @@
 import pytest
 from dirty_equals import HasRepr, IsStr
 from pydantic_core import CoreSchema, core_schema
-from typing_extensions import Annotated, Literal, OrderedDict, TypeVarTuple, Unpack, get_args
+from typing_extensions import Annotated, Literal, OrderedDict, ParamSpec, TypeVarTuple, Unpack, get_args
 
 from pydantic import (
     BaseModel,
@@ -2534,3 +2534,20 @@ class Container(BaseModel, Generic[T]):
 
     assert Container[type(None)](value=None).value is None
     assert Container[None](value=None).value is None
+
+
+@pytest.mark.skipif(platform.python_implementation() == 'PyPy', reason='PyPy does not allow ParamSpec in generics')
+def test_paramspec_is_usable():
+    # This used to cause a recursion error due to `P in P is True`
+    # This test doesn't actually test that ParamSpec works properly for validation or anything.
+
+    P = ParamSpec('P')
+
+    class MyGenericParamSpecClass(Generic[P]):
+        def __init__(self, func: Callable[P, None], *args: P.args, **kwargs: P.kwargs) -> None:
+            super().__init__()
+
+    class ParamSpecGenericModel(BaseModel, Generic[P]):
+        my_generic: MyGenericParamSpecClass[P]
+
+        model_config = dict(arbitrary_types_allowed=True)