Add a bit more support for PEP 612 in stubs.

This is to unblock python/typeshed#6221.
Also see #786.

PiperOrigin-RevId: 407168815

pytype/pyi/definitions.py

@@ -511,23 +511,31 @@ def _parameterized_type(self, base_type: Any, parameters):
         raise ParseError("[..., ...] not supported")
       return pytd.GenericType(base_type=base_type, parameters=(element_type,))
     else:
-      parameters = tuple(pytd.AnythingType() if p is self.ELLIPSIS else p
-                         for p in parameters)
+      processed_parameters = []
+      # We do not yet support PEP 612, Parameter Specification Variables.
+      # To avoid blocking typeshed from adopting this PEP, we convert new
+      # features to approximations that only use supported features.
+      for p in parameters:
+        if p is self.ELLIPSIS:
+          processed = pytd.AnythingType()
+        elif (p in self.param_specs and
+              self._matches_full_name(base_type, "typing.Generic")):
+          # Replacing a ParamSpec with a TypeVar isn't correct, but it'll work
+          # for simple cases in which the filled value is also a ParamSpec.
+          self.type_params.append(pytd.TypeParameter(p.name))
+          processed = p
+        elif (p in self.param_specs or
+              (isinstance(p, pytd.GenericType) and
+               self._matches_full_name(p, _CONCATENATE_TYPES))):
+          processed = pytd.AnythingType()
+        else:
+          processed = p
+        processed_parameters.append(processed)
+      parameters = tuple(processed_parameters)
       if self._matches_named_type(base_type, _TUPLE_TYPES):
         return pytdgen.heterogeneous_tuple(base_type, parameters)
       elif self._matches_named_type(base_type, _CALLABLE_TYPES):
-        callable_parameters = []
-        for p in parameters:
-          # We do not yet support PEP 612, Parameter Specification Variables.
-          # To avoid blocking typeshed from adopting this PEP, we convert new
-          # features to Any.
-          if p in self.param_specs or (
-              isinstance(p, pytd.GenericType) and
-              self._matches_full_name(p, _CONCATENATE_TYPES)):
-            callable_parameters.append(pytd.AnythingType())
-          else:
-            callable_parameters.append(p)
-        return pytdgen.pytd_callable(base_type, tuple(callable_parameters))
+        return pytdgen.pytd_callable(base_type, parameters)
       else:
         assert parameters
         return pytd.GenericType(base_type=base_type, parameters=parameters)
@@ -558,7 +566,7 @@ def resolve_type(self, name: Union[str, pytd_node.Node]) -> pytd.Type:
   def new_type(
       self,
       name: Union[str, pytd_node.Node],
-      parameters: Optional[List[pytd_node.Node]] = None
+      parameters: Optional[List[pytd.Type]] = None
   ) -> pytd.Type:
     """Return the AST for a type.
 

pytype/pyi/parser_test.py

@@ -2851,7 +2851,6 @@ def f(x: Callable[P, R]) -> Callable[P, Awaitable[R]]: ...
       def f(x: Callable[..., R]) -> Callable[..., Awaitable[R]]: ...
     """)
 
-  @test_base.skip("ParamSpec in custom generic classes not supported yet")
   def test_custom_generic(self):
     self.check("""
       from typing import Callable, Generic, ParamSpec, TypeVar
@@ -2862,6 +2861,38 @@ def test_custom_generic(self):
       class X(Generic[T, P]):
           f: Callable[P, int]
           x: T
+    """, """
+      from typing import Callable, Generic, TypeVar
+
+      P = TypeVar('P')
+      T = TypeVar('T')
+
+      class X(Generic[T, P]):
+          f: Callable[..., int]
+          x: T
+    """)
+
+  def test_use_custom_generic(self):
+    self.check("""
+      from typing import Callable, Generic, TypeVar
+      from typing_extensions import ParamSpec
+
+      _T = TypeVar('_T')
+      _P = ParamSpec('_P')
+
+      class Foo(Generic[_P, _T]): ...
+
+      def f(x: Callable[_P, _T]) -> Foo[_P, _T]: ...
+    """, """
+      from typing import Any, Callable, Generic, TypeVar
+      from typing_extensions import ParamSpec
+
+      _P = TypeVar('_P')
+      _T = TypeVar('_T')
+
+      class Foo(Generic[_P, _T]): ...
+
+      def f(x: Callable[..., _T]) -> Foo[Any, _T]: ...
     """)
 
   @test_base.skip("ParamSpec in custom generic classes not supported yet")