Fix subclass check on union metatype.

Issue: #144

Author: coady

multimethod/__init__.py

@@ -88,7 +88,9 @@ def __hash__(self) -> int:
 
     def __subclasscheck__(self, subclass):
         args = get_args(subclass)
-        match origin := get_origin(subclass) or subclass:
+        match origin := get_origin(subclass):
+            case None:
+                origin = subclass
             case typing.Literal:
                 return all(isinstance(arg, self) for arg in args)
             case typing.Union | types.UnionType:

tests/test_subscripts.py

@@ -39,6 +39,7 @@ def test_union():
     assert issubclass(int, subtype(int | float))
     assert issubclass(subtype(int | float), subtype(int | float | None))
     assert subtype(Iterable | Mapping | Sequence) is Iterable
+    assert not issubclass(Union, subtype(type[int]))
 
     # Test nested subtype with UnionType base
     tp = subtype(int | float)
@@ -77,10 +78,15 @@ def func(_: cls[int]): ...
 
     @func.register
     def _(_: type[cls[int]]):
+        return int
+
+    @func.register
+    def _(_: type[cls]):
         return type
 
     assert func(cls[int]()) is None
-    assert func(cls[int]) is type
+    assert func(cls[int]) is int
+    assert func(cls) is type
 
 
 def test_tuple():