From 15537c51c188a6633248c25d211d5216e673aee3 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Wed, 13 Apr 2022 06:08:49 +0300
Subject: bpo-43224: Forbid TypeVar substitution with Unpack (GH-32031)

---
 Lib/test/test_typing.py | 14 ++++++++++++++
 Lib/typing.py           |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 2afa544..97fc66a 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -562,6 +562,20 @@ class TypeVarTupleTests(BaseTestCase):
             self.assertEqual(E[float, str, int, bytes],
                              Tuple[List[float], A[str, int], List[bytes]])
 
+    def test_bad_var_substitution(self):
+        Ts = TypeVarTuple('Ts')
+        T = TypeVar('T')
+        T2 = TypeVar('T2')
+        class G(Generic[Unpack[Ts]]): pass
+
+        for A in G, Tuple:
+            B = A[T, Unpack[Ts], str, T2]
+            with self.assertRaises(TypeError):
+                B[int, Unpack[Ts]]
+            C = A[T, Unpack[Ts], str, T2]
+            with self.assertRaises(TypeError):
+                C[int, Unpack[Ts], Unpack[Ts]]
+
     def test_repr_is_correct(self):
         Ts = TypeVarTuple('Ts')
         self.assertEqual(repr(Ts), 'Ts')
diff --git a/Lib/typing.py b/Lib/typing.py
index 46fc722..1b584be 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -965,6 +965,8 @@ class TypeVar(_Final, _Immutable, _BoundVarianceMixin, _root=True):
     def __typing_subst__(self, arg):
         msg = "Parameters to generic types must be types."
         arg = _type_check(arg, msg, is_argument=True)
+        if (isinstance(arg, _GenericAlias) and arg.__origin__ is Unpack):
+            raise TypeError(f"{arg} is not valid as type argument")
         return arg
 
 
-- 
cgit v0.12