gh-101015: Fix typing.ForwardRef with *tuple unpack

Author: sobolevn

Lib/test/test_typing.py

@@ -1224,6 +1224,22 @@ class D(Generic[Unpack[Ts]]): pass
         self.assertIs(D[T].__origin__, D)
         self.assertIs(D[Unpack[Ts]].__origin__, D)
 
+    def test_get_type_hints_on_unpack_args(self):
+        Ts = TypeVarTuple('Ts')
+
+        def func1(*args: '*Ts'): pass
+        self.assertEqual(gth(func1, localns={'Ts': Ts}),
+                        {'args': Unpack[Ts]})
+
+        def func2(*args: '*tuple[int, str]'): pass
+        self.assertEqual(gth(func2), {'args': Unpack[tuple[int, str]]})
+
+        class CustomVariadic(Generic[*Ts]): pass
+
+        def func3(*args: '*CustomVariadic[int, str]'): pass
+        self.assertEqual(gth(func3, localns={'CustomVariadic': CustomVariadic}),
+                         {'args': Unpack[CustomVariadic[int, str]]})
+
     def test_tuple_args_are_correct(self):
         Ts = TypeVarTuple('Ts')
 

Lib/typing.py

@@ -818,7 +818,7 @@ class ForwardRef(_Final, _root=True):
     __slots__ = ('__forward_arg__', '__forward_code__',
                  '__forward_evaluated__', '__forward_value__',
                  '__forward_is_argument__', '__forward_is_class__',
-                 '__forward_module__')
+                 '__forward_module__', '__forward_is_unpack__')
 
     def __init__(self, arg, is_argument=True, module=None, *, is_class=False):
         if not isinstance(arg, str):
@@ -828,9 +828,11 @@ def __init__(self, arg, is_argument=True, module=None, *, is_class=False):
         # Unfortunately, this isn't a valid expression on its own, so we
         # do the unpacking manually.
         if arg[0] == '*':
-            arg_to_compile = f'({arg},)[0]'  # E.g. (*Ts,)[0]
+            arg_to_compile = f'({arg},)[0]'  # E.g. (*Ts,)[0] or (tuple[int, int],)[0]
+            is_unpack = True
         else:
             arg_to_compile = arg
+            is_unpack = False
         try:
             code = compile(arg_to_compile, '<string>', 'eval')
         except SyntaxError:
@@ -843,6 +845,7 @@ def __init__(self, arg, is_argument=True, module=None, *, is_class=False):
         self.__forward_is_argument__ = is_argument
         self.__forward_is_class__ = is_class
         self.__forward_module__ = module
+        self.__forward_is_unpack__ = is_unpack
 
     def _evaluate(self, globalns, localns, recursive_guard):
         if self.__forward_arg__ in recursive_guard:
@@ -867,6 +870,11 @@ def _evaluate(self, globalns, localns, recursive_guard):
             self.__forward_value__ = _eval_type(
                 type_, globalns, localns, recursive_guard | {self.__forward_arg__}
             )
+            if (
+                self.__forward_is_unpack__ and
+                not isinstance(self.__forward_value__, _UnpackGenericAlias)
+            ):
+                self.__forward_value__ = Unpack[self.__forward_value__]
             self.__forward_evaluated__ = True
         return self.__forward_value__
 

Misc/NEWS.d/next/Library/2023-01-14-12-58-21.gh-issue-101015.stWFid.rst

@@ -0,0 +1,2 @@
+Fix :class:`typing.ForwardRef` evaluation of ``'*tuple[...]'`` string. It
+must not drop the ``Unpack`` part.