Support ParamSpec for TypeAliasType (#449)

Co-authored-by: Alex Waygood <[email protected]>

Author: Daraan

CHANGELOG.md

@@ -26,6 +26,9 @@ aliases that have a `Concatenate` special form as their argument.
 - Backport CPython PR [#124795](https://github.com/python/cpython/pull/124795):
   fix `TypeAliasType` not raising an error on non-tuple inputs for `type_params`.
   Patch by [Daraan](https://github.com/Daraan).
+- Fix that lists and ... could not be used for parameter expressions for `TypeAliasType`
+  instances before Python 3.11.
+  Patch by [Daraan](https://github.com/Daraan).
 
 # Release 4.12.2 (June 7, 2024)
 

src/test_typing_extensions.py

@@ -7267,6 +7267,80 @@ def test_attributes(self):
         self.assertEqual(Variadic.__type_params__, (Ts,))
         self.assertEqual(Variadic.__parameters__, tuple(iter(Ts)))
 
+        P = ParamSpec('P')
+        CallableP = TypeAliasType("CallableP", Callable[P, Any], type_params=(P, ))
+        self.assertEqual(CallableP.__name__, "CallableP")
+        self.assertEqual(CallableP.__value__,  Callable[P, Any])
+        self.assertEqual(CallableP.__type_params__, (P,))
+        self.assertEqual(CallableP.__parameters__, (P,))
+
+    def test_alias_types_and_substitutions(self):
+        T = TypeVar('T')
+        T2 = TypeVar('T2')
+        T_default = TypeVar("T_default", default=int)
+        Ts = TypeVarTuple("Ts")
+        P = ParamSpec('P')
+
+        test_argument_cases = {
+            # arguments : expected parameters
+            int : (),
+            ... : (),
+            None : (),
+            T2 : (T2,),
+            Union[int, List[T2]] : (T2,),
+            Tuple[int, str] : (),
+            Tuple[T, T_default, T2] : (T, T_default, T2),
+            Tuple[Unpack[Ts]] : (Ts,),
+            Callable[[Unpack[Ts]], T2] : (Ts, T2),
+            Callable[P, T2] : (P, T2),
+            Callable[Concatenate[T2,  P], T_default] : (T2, P, T_default),
+            TypeAliasType("NestedAlias", List[T], type_params=(T,))[T2] : (T2,),
+            Unpack[Ts] : (Ts,),
+            Unpack[Tuple[int, T2]] : (T2,),
+            Concatenate[int,  P] : (P,),
+            # Not tested usage of bare TypeVarTuple, would need 3.11+
+            # Ts : (Ts,),  # invalid case
+        }
+
+        test_alias_cases = [
+            # Simple cases
+            TypeAliasType("ListT", List[T], type_params=(T,)),
+            TypeAliasType("UnionT", Union[int, List[T]], type_params=(T,)),
+            # Value has no parameter but in type_param
+            TypeAliasType("ValueWithoutT", int, type_params=(T,)),
+            # Callable
+            TypeAliasType("CallableP", Callable[P, Any], type_params=(P, )),
+            TypeAliasType("CallableT", Callable[..., T], type_params=(T, )),
+            TypeAliasType("CallableTs", Callable[[Unpack[Ts]], Any], type_params=(Ts, )),
+            # TypeVarTuple
+            TypeAliasType("Variadic", Tuple[int, Unpack[Ts]], type_params=(Ts,)),
+            # TypeVar with default
+            TypeAliasType("TupleT_default", Tuple[T_default, T], type_params=(T, T_default)),
+            TypeAliasType("CallableT_default", Callable[[T], T_default], type_params=(T, T_default)),
+        ]
+
+        for alias in test_alias_cases:
+            with self.subTest(alias=alias, args=[]):
+                subscripted = alias[[]]
+                self.assertEqual(get_args(subscripted), ([],))
+                self.assertEqual(subscripted.__parameters__, ())
+            with self.subTest(alias=alias, args=()):
+                subscripted = alias[()]
+                self.assertEqual(get_args(subscripted), ())
+                self.assertEqual(subscripted.__parameters__, ())
+            with self.subTest(alias=alias, args=(int, float)):
+                subscripted = alias[int, float]
+                self.assertEqual(get_args(subscripted), (int, float))
+                self.assertEqual(subscripted.__parameters__, ())
+            with self.subTest(alias=alias, args=[int, float]):
+                subscripted = alias[[int, float]]
+                self.assertEqual(get_args(subscripted), ([int, float],))
+                self.assertEqual(subscripted.__parameters__, ())
+            for expected_args, expected_parameters in test_argument_cases.items():
+                with self.subTest(alias=alias, args=expected_args):
+                    self.assertEqual(get_args(alias[expected_args]), (expected_args,))
+                    self.assertEqual(alias[expected_args].__parameters__, expected_parameters)
+
     def test_cannot_set_attributes(self):
         Simple = TypeAliasType("Simple", int)
         with self.assertRaisesRegex(AttributeError, "readonly attribute"):
@@ -7327,12 +7401,19 @@ def test_or(self):
             Alias | "Ref"
 
     def test_getitem(self):
+        T = TypeVar('T')
         ListOrSetT = TypeAliasType("ListOrSetT", Union[List[T], Set[T]], type_params=(T,))
         subscripted = ListOrSetT[int]
         self.assertEqual(get_args(subscripted), (int,))
         self.assertIs(get_origin(subscripted), ListOrSetT)
-        with self.assertRaises(TypeError):
-            subscripted[str]
+        with self.assertRaisesRegex(TypeError,
+                                    "not a generic class"
+                                    # types.GenericAlias raises a different error in 3.10
+                                    if sys.version_info[:2] != (3, 10)
+                                    else "There are no type variables left in ListOrSetT"
+        ):
+            subscripted[int]
+
 
         still_generic = ListOrSetT[Iterable[T]]
         self.assertEqual(get_args(still_generic), (Iterable[T],))
@@ -7341,6 +7422,114 @@ def test_getitem(self):
         self.assertEqual(get_args(fully_subscripted), (Iterable[float],))
         self.assertIs(get_origin(fully_subscripted), ListOrSetT)
 
+        ValueWithoutTypeVar = TypeAliasType("ValueWithoutTypeVar", int, type_params=(T,))
+        still_subscripted = ValueWithoutTypeVar[str]
+        self.assertEqual(get_args(still_subscripted), (str,))
+
+    def test_callable_without_concatenate(self):
+        P = ParamSpec('P')
+        CallableP = TypeAliasType("CallableP", Callable[P, Any], type_params=(P,))
+        get_args_test_cases = [
+            # List of (alias, expected_args)
+            # () -> Any
+            (CallableP[()], ()),
+            (CallableP[[]], ([],)),
+            # (int) -> Any
+            (CallableP[int], (int,)),
+            (CallableP[[int]], ([int],)),
+            # (int, int) -> Any
+            (CallableP[int, int],  (int, int)),
+            (CallableP[[int, int]], ([int, int],)),
+            # (...) -> Any
+            (CallableP[...], (...,)),
+            # (int, ...) -> Any
+            (CallableP[[int, ...]], ([int, ...],)),
+        ]
+
+        for index, (expression, expected_args) in enumerate(get_args_test_cases):
+            with self.subTest(index=index, expression=expression):
+                self.assertEqual(get_args(expression), expected_args)
+
+        self.assertEqual(CallableP[...], CallableP[(...,)])
+        # (T) -> Any
+        CallableT = CallableP[T]
+        self.assertEqual(get_args(CallableT), (T,))
+        self.assertEqual(CallableT.__parameters__, (T,))
+
+    def test_callable_with_concatenate(self):
+        P = ParamSpec('P')
+        P2 = ParamSpec('P2')
+        CallableP = TypeAliasType("CallableP", Callable[P, Any], type_params=(P,))
+
+        callable_concat = CallableP[Concatenate[int, P2]]
+        self.assertEqual(callable_concat.__parameters__, (P2,))
+        concat_usage = callable_concat[str]
+        with self.subTest("get_args of Concatenate in TypeAliasType"):
+            if not TYPING_3_9_0:
+                # args are: ([<class 'int'>, ~P2],)
+                self.skipTest("Nested ParamSpec is not substituted")
+            if sys.version_info < (3, 10, 2):
+                self.skipTest("GenericAlias keeps Concatenate in __args__ prior to 3.10.2")
+            self.assertEqual(get_args(concat_usage), ((int, str),))
+        with self.subTest("Equality of parameter_expression without []"):
+            if not TYPING_3_10_0:
+                self.skipTest("Nested list is invalid type form")
+            self.assertEqual(concat_usage, callable_concat[[str]])
+
+    def test_substitution(self):
+        T = TypeVar('T')
+        Ts = TypeVarTuple("Ts")
+
+        CallableTs = TypeAliasType("CallableTs", Callable[[Unpack[Ts]], Any], type_params=(Ts, ))
+        unpack_callable = CallableTs[Unpack[Tuple[int, T]]]
+        self.assertEqual(get_args(unpack_callable), (Unpack[Tuple[int, T]],))
+
+        P = ParamSpec('P')
+        CallableP = TypeAliasType("CallableP", Callable[P, T], type_params=(P, T))
+        callable_concat = CallableP[Concatenate[int, P], Any]
+        self.assertEqual(get_args(callable_concat), (Concatenate[int, P], Any))
+
+    def test_wrong_amount_of_parameters(self):
+        T = TypeVar('T')
+        T2 = TypeVar("T2")
+        P = ParamSpec('P')
+        ListOrSetT = TypeAliasType("ListOrSetT", Union[List[T], Set[T]], type_params=(T,))
+        TwoT = TypeAliasType("TwoT", Union[List[T], Set[T2]], type_params=(T, T2))
+        CallablePT = TypeAliasType("CallablePT", Callable[P, T], type_params=(P, T))
+
+        # Not enough parameters
+        test_cases = [
+            # not_enough
+            (TwoT[int],                              [(int,), ()]),
+            (TwoT[T],                                [(T,), (T,)]),
+            # callable and not enough
+            (CallablePT[int],                        [(int,), ()]),
+            # too many
+            (ListOrSetT[int, bool],                  [(int, bool), ()]),
+            # callable and too many
+            (CallablePT[str, float, int],            [(str, float, int), ()]),
+            # Check if TypeVar is still present even if over substituted
+            (ListOrSetT[int, T],                     [(int, T), (T,)]),
+            # With and without list for ParamSpec
+            (CallablePT[str, float, T],              [(str, float, T), (T,)]),
+            (CallablePT[[str], float, int, T2],      [([str], float, int, T2), (T2,)]),
+        ]
+
+        for index, (alias, [expected_args, expected_params]) in enumerate(test_cases):
+            with self.subTest(index=index, alias=alias):
+                self.assertEqual(get_args(alias), expected_args)
+                self.assertEqual(alias.__parameters__, expected_params)
+
+    # The condition should align with the version of GeneriAlias usage in __getitem__ or be 3.11+
+    @skipIf(TYPING_3_10_0, "Most arguments are allowed in 3.11+ or with GenericAlias")
+    def test_invalid_cases_before_3_10(self):
+        T = TypeVar('T')
+        ListOrSetT = TypeAliasType("ListOrSetT", Union[List[T], Set[T]], type_params=(T,))
+        with self.assertRaises(TypeError):
+            ListOrSetT[Generic[T]]
+        with self.assertRaises(TypeError):
+            ListOrSetT[(Generic[T], )]
+
     def test_unpack_parameter_collection(self):
         Ts = TypeVarTuple("Ts")
 

src/typing_extensions.py

@@ -3662,6 +3662,33 @@ def _raise_attribute_error(self, name: str) -> Never:
         def __repr__(self) -> str:
             return self.__name__
 
+        if sys.version_info < (3, 11):
+            def _check_single_param(self, param, recursion=0):
+                # Allow [], [int], [int, str], [int, ...], [int, T]
+                if param is ...:
+                    return ...
+                if param is None:
+                    return None
+                # Note in <= 3.9 _ConcatenateGenericAlias inherits from list
+                if isinstance(param, list) and recursion == 0:
+                    return [self._check_single_param(arg, recursion+1)
+                            for arg in param]
+                return typing._type_check(
+                        param, f'Subscripting {self.__name__} requires a type.'
+                    )
+
+        def _check_parameters(self, parameters):
+            if sys.version_info < (3, 11):
+                return tuple(
+                    self._check_single_param(item)
+                    for item in parameters
+                )
+            return tuple(typing._type_check(
+                        item, f'Subscripting {self.__name__} requires a type.'
+                    )
+                    for item in parameters
+            )
+
         def __getitem__(self, parameters):
             if not self.__type_params__:
                 raise TypeError("Only generic type aliases are subscriptable")
@@ -3670,13 +3697,14 @@ def __getitem__(self, parameters):
             # Using 3.9 here will create problems with Concatenate
             if sys.version_info >= (3, 10):
                 return _types.GenericAlias(self, parameters)
-            parameters = tuple(
-                typing._type_check(
-                    item, f'Subscripting {self.__name__} requires a type.'
-                )
-                for item in parameters
-            )
-            return _TypeAliasGenericAlias(self, parameters)
+            type_vars = _collect_type_vars(parameters)
+            parameters = self._check_parameters(parameters)
+            alias = _TypeAliasGenericAlias(self, parameters)
+            # alias.__parameters__ is not complete if Concatenate is present
+            # as it is converted to a list from which no parameters are extracted.
+            if alias.__parameters__ != type_vars:
+                alias.__parameters__ = type_vars
+            return alias
 
         def __reduce__(self):
             return self.__name__