fix crash with nested tuple

Author: randolf-scholz

mypy/typeanal.py

@@ -1964,7 +1964,7 @@ def check_unpacks_in_list(self, items: list[Type]) -> list[Type]:
         new_items: list[Type] = []
         num_unpacks = 0
         final_unpack = None
-        for item in items:
+        for item in flatten_nested_tuples(items):
             # TODO: handle forward references here, they appear as Unpack[Any].
             if isinstance(item, UnpackType) and not isinstance(
                 get_proper_type(item.type), TupleType
@@ -1978,7 +1978,7 @@ def check_unpacks_in_list(self, items: list[Type]) -> list[Type]:
 
         if num_unpacks > 1:
             assert final_unpack is not None
-            self.fail("More than one Unpack in a type is not allowed", final_unpack.type)
+            self.fail("More than one variable Unpack in a type is not allowed", final_unpack.type)
         return new_items
 
     def tuple_type(self, items: list[Type], line: int, column: int) -> TupleType:

test-data/unit/check-python312.test

@@ -2039,6 +2039,7 @@ class Z: ...  # E: Name "Z" already defined on line 2
 class A[*Ts]: ...
 
 A[*tuple[int, ...], *tuple[int, ...]]  # E: More than one Unpack in a type is not allowed
+A[*tuple[*tuple[int, ...]], *tuple[*tuple[int, ...]]]  # E: More than one Unpack in a type is not allowed
 a: A[*tuple[int, ...], *tuple[int, ...]]  # E: More than one Unpack in a type is not allowed
 def foo(a: A[*tuple[int, ...], *tuple[int, ...]]): ...  # E: More than one Unpack in a type is not allowed