Support subscription of Callable[Concatenate[P], Any] with ... in Python 3.10

CHANGELOG.md

@@ -16,6 +16,9 @@
   subscripted objects) had wrong parameters if they were directly
   subscripted with an `Unpack` object.
   Patch by [Daraan](https://github.com/Daraan).
+- Backport to Python 3.10 the ability to substitute `...` in generic `Callable`
+aliases that have a `Concatenate` special form as their argument.
+  Patch by [Daraan](https://github.com/Daraan).
 - Fix error in subscription of `Unpack` aliases causing nested Unpacks 
   to not be resolved correctly. Patch by [Daraan](https://github.com/Daraan).
 

src/test_typing_extensions.py

@@ -5401,6 +5401,18 @@ def test_invalid_uses(self):
             ):
                 Concatenate[1, P]
 
+    @skipUnless(TYPING_3_10_0, "Missing backport to <=3.9. See issue #48")
+    def test_alias_subscription_with_ellipsis(self):
+        P = ParamSpec('P')
+        X = Callable[Concatenate[int, P], Any]
+
+        C1 = X[...]
+        self.assertEqual(C1.__parameters__, ())
+        with self.subTest("Compare Concatenate[int, ...]"):
+            if sys.version_info[:2] == (3, 10):
+                self.skipTest("Needs Issue #110 | PR #481: construct Concatenate with ...")
+            self.assertEqual(get_args(C1), (Concatenate[int, ...], Any))
+
     def test_basic_introspection(self):
         P = ParamSpec('P')
         C1 = Concatenate[int, P]
@@ -6130,7 +6142,7 @@ def test_typing_extensions_defers_when_possible(self):
         if sys.version_info < (3, 10, 1):
             exclude |= {"Literal"}
         if sys.version_info < (3, 11):
-            exclude |= {'final', 'Any', 'NewType', 'overload'}
+            exclude |= {'final', 'Any', 'NewType', 'overload', 'Concatenate'}
         if sys.version_info < (3, 12):
             exclude |= {
                 'SupportsAbs', 'SupportsBytes',

src/typing_extensions.py

@@ -1795,28 +1795,52 @@ def __parameters__(self):
             return tuple(
                 tp for tp in self.__args__ if isinstance(tp, (typing.TypeVar, ParamSpec))
             )
+# 3.10+
+else:
+    _ConcatenateGenericAlias = typing._ConcatenateGenericAlias
 
+    # 3.10
+    if sys.version_info < (3, 11):
+        _typing_ConcatenateGenericAlias = _ConcatenateGenericAlias
 
-# 3.8-3.9
+        class _ConcatenateGenericAlias(_typing_ConcatenateGenericAlias, _root=True):
+            # needed for checks in collections.abc.Callable to accept this class
+            __module__ = "typing"
+
+            def copy_with(self, params):
+                if isinstance(params[-1], (list, tuple)):
+                    return (*params[:-1], *params[-1])
+                if isinstance(params[-1], _ConcatenateGenericAlias):
+                    params = (*params[:-1], *params[-1].__args__)
+                elif not (params[-1] is ... or isinstance(params[-1], ParamSpec)):
+                    raise TypeError("The last parameter to Concatenate should be a "
+                            "ParamSpec variable or ellipsis.")
+                return super(_typing_ConcatenateGenericAlias, self).copy_with(params)
+
+
+# 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):
+    elif 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)
+    if (3, 10, 2) < sys.version_info < (3, 11):
+        return _ConcatenateGenericAlias(self, parameters,
+                                 _typevar_types=(TypeVar, ParamSpec),
+                                 _paramspec_tvars=True)
     return _ConcatenateGenericAlias(self, parameters)
 
 
-# 3.10+
-if hasattr(typing, 'Concatenate'):
+# 3.11+
+if sys.version_info >= (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):