Concatenate supports ellipsis in python3.10

Author: Daraan

src/typing_extensions.py

@@ -1773,7 +1773,7 @@ class _ConcatenateGenericAlias(list):
         # Flag in 3.8.
         _special = False
 
-        def __init__(self, origin, args):
+        def __init__(self, origin, args, _typevar_types=(TypeVar, ParamSpec), _paramspec_tvars=True):
             super().__init__(args)
             self.__origin__ = origin
             self.__args__ = args
@@ -1795,28 +1795,30 @@ def __parameters__(self):
             return tuple(
                 tp for tp in self.__args__ if isinstance(tp, (typing.TypeVar, ParamSpec))
             )
+# 3.10+
+else:
+    _ConcatenateGenericAlias = typing._ConcatenateGenericAlias  # noqa: F811
 
-
-# 3.8-3.9
+# 3.8-3.10
 @typing._tp_cache
 def _concatenate_getitem(self, parameters):
     if parameters == ():
         raise TypeError("Cannot take a Concatenate of no types.")
     if not isinstance(parameters, tuple):
         parameters = (parameters,)
-    if not isinstance(parameters[-1], ParamSpec):
+    if not (parameters[-1] is ... or isinstance(parameters[-1], ParamSpec)):
         raise TypeError("The last parameter to Concatenate should be a "
-                        "ParamSpec variable.")
+                        "ParamSpec variable or ellipsis.")
     msg = "Concatenate[arg, ...]: each arg must be a type."
-    parameters = tuple(typing._type_check(p, msg) for p in parameters)
-    return _ConcatenateGenericAlias(self, parameters)
+    parameters = (*(typing._type_check(p, msg) for p in parameters[:-1]), parameters[-1])
+    return _ConcatenateGenericAlias(self, parameters,
+                                    _typevar_types=(TypeVar, ParamSpec),
+                                    _paramspec_tvars=True)
 
-
-# 3.10+
-if hasattr(typing, 'Concatenate'):
+# 3.11+; Concatenate does not accept ellipsis in 3.10
+if hasattr(typing, 'Concatenate') and sys.version_info[:2] >= (3, 11):
     Concatenate = typing.Concatenate
-    _ConcatenateGenericAlias = typing._ConcatenateGenericAlias
-# 3.9
+# 3.9-3.10
 elif sys.version_info[:2] >= (3, 9):
     @_ExtensionsSpecialForm
     def Concatenate(self, parameters):