fix: Fix checking sublcasses of Future (#665)

* fix: Fix checking sublcasses of Future

* skip test on python 3.8

* add negative test

src/magicgui/_util.py

@@ -210,10 +210,11 @@ def safe_issubclass(obj: object, superclass: object) -> bool:
         if obj_origin is tuple and obj_args:
             return _safe_isinstance_tuple(obj, superclass)
 
-        return (
-                issubclass(obj_origin, superclass_origin) and  # type: ignore
-                (obj_args == superclass_args or not superclass_args)
-        )
+        if not superclass_args:
+            return True
+        if len(obj_args) != len(superclass_args):
+            return False
+        return all(safe_issubclass(o, s) for o, s in zip(obj_args, superclass_args))
 
     except Exception:
         return False

tests/test_util.py

@@ -1,6 +1,7 @@
 import sys
 import typing
 from collections.abc import Mapping, Sequence
+from concurrent.futures import Future
 
 import pytest
 
@@ -78,3 +79,10 @@ def test_tuple_check(self):
         assert safe_issubclass(typing.Tuple[int, int], typing.Tuple[int, ...])
         assert not safe_issubclass(typing.Tuple[int, int], typing.Tuple[int, str])
         assert not safe_issubclass(typing.Tuple[int, int], typing.Tuple[int, int, int])
+
+    @pytest.mark.skipif(sys.version_info < (3, 9), reason="Future[] is supported in 3.9+")
+    def test_subclass_future(self):
+        assert safe_issubclass(Future[typing.List[int]], Future[list[int]])
+        assert safe_issubclass(Future[typing.List[int]], Future[list])
+        assert safe_issubclass(Future[list[int]], Future[typing.List[int]])
+        assert not safe_issubclass(Future[list[int]], Future[typing.List[str]])