_collect_type_vars should not collect Unpack objects itself (#472)

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

CHANGELOG.md

@@ -12,6 +12,10 @@
 - Fix bug where a subscripted `TypeAliasType` instance did not have all
   attributes of the original `TypeAliasType` instance on older Python versions.
   Patch by [Daraan](https://github.com/Daraan) and Alex Waygood.
+- Fix bug where subscripted `TypeAliasType` instances (and some other
+  subscripted objects) had wrong parameters if they were directly
+  subscripted with an `Unpack` object.
+  Patch by [Daraan](https://github.com/Daraan).
 
 # Release 4.12.2 (June 7, 2024)
 

src/test_typing_extensions.py

@@ -7247,6 +7247,21 @@ def test_getitem(self):
         self.assertEqual(get_args(fully_subscripted), (Iterable[float],))
         self.assertIs(get_origin(fully_subscripted), ListOrSetT)
 
+    def test_unpack_parameter_collection(self):
+        Ts = TypeVarTuple("Ts")
+
+        class Foo(Generic[Unpack[Ts]]):
+            bar: Tuple[Unpack[Ts]]
+
+        FooAlias = TypeAliasType("FooAlias", Foo[Unpack[Ts]], type_params=(Ts,))
+        self.assertEqual(FooAlias[Unpack[Tuple[str]]].__parameters__, ())
+        self.assertEqual(FooAlias[Unpack[Tuple[T]]].__parameters__, (T,))
+
+        P = ParamSpec("P")
+        CallableP = TypeAliasType("CallableP", Callable[P, Any], type_params=(P,))
+        call_int_T = CallableP[Unpack[Tuple[int, T]]]
+        self.assertEqual(call_int_T.__parameters__, (T,))
+
     def test_alias_attributes(self):
         T = TypeVar('T')
         T2 = TypeVar('T2')

src/typing_extensions.py

@@ -3068,7 +3068,10 @@ def _collect_type_vars(types, typevar_types=None):
         for t in types:
             if _is_unpacked_typevartuple(t):
                 type_var_tuple_encountered = True
-            elif isinstance(t, typevar_types) and t not in tvars:
+            elif (
+                isinstance(t, typevar_types) and not isinstance(t, _UnpackAlias)
+                and t not in tvars
+            ):
                 if enforce_default_ordering:
                     has_default = getattr(t, '__default__', NoDefault) is not NoDefault
                     if has_default: