Support instances of Generic types in propertyhelperwip/jtojnar/gio-generic-list

Subscribing a subclass of `Generic[...]` (e.g. `Gio.ListStore[Gio.File]`)
will turn it into instance of `typing._GenericAlias`.
That is not an instance of `type`, nor a subclass of the subscribed class.

To allow passing instantiated generic types as `type` argument of `Property`,
we need to extract the generic type, or property will fail with `Unsupported type` error.

Unfortunately, `typing` module only provides helper for that since Python 3.8
so we need to create our own `get_origin` that looks into internal state for 3.7.

2 files changed, 30 insertions, 6 deletions

diff --git a/gi/_propertyhelper.py b/gi/_propertyhelper.py
index def34b22..69357553 100644
--- a/gi/_propertyhelper.py
+++ b/gi/_propertyhelper.py
@@ -26,6 +26,21 @@ from ._constants import \
     TYPE_POINTER, TYPE_BOXED, TYPE_PARAM, TYPE_OBJECT, \
     TYPE_PYOBJECT, TYPE_GTYPE, TYPE_STRV, TYPE_VARIANT
 
+
+from typing import Optional
+try:
+    # Only available in Python 3.8 or later.
+    from typing import get_origin
+except ImportError:
+    from typing import _GenericAlias
+
+    def get_origin(type_: object) -> Optional[type]:
+        """Get the unsubscripted version of a type."""
+        if isinstance(type_, _GenericAlias):
+            return type_.__origin__
+        return None
+
+
 G_MAXFLOAT = _gi.G_MAXFLOAT
 G_MAXDOUBLE = _gi.G_MAXDOUBLE
 G_MININT = _gi.G_MININT
@@ -249,12 +264,18 @@ class Property(object):
     def _type_from_python(self, type_):
         if type_ in self._type_from_pytype_lookup:
             return self._type_from_pytype_lookup[type_]
-        elif (isinstance(type_, type) and
-              issubclass(type_, (_gi.GObject,
-                                 _gi.GEnum,
-                                 _gi.GFlags,
-                                 _gi.GBoxed,
-                                 _gi.GInterface))):
+
+        # Support instances of generic types such as Gio.ListStore[Gio.File]
+        origin = get_origin(type_)
+        if origin is not None:
+            type_ = origin
+
+        if (isinstance(type_, type) and
+            issubclass(type_, (_gi.GObject,
+                               _gi.GEnum,
+                               _gi.GFlags,
+                               _gi.GBoxed,
+                               _gi.GInterface))):
             return type_.__gtype__
         elif type_ in (TYPE_NONE, TYPE_INTERFACE, TYPE_CHAR, TYPE_UCHAR,
                        TYPE_INT, TYPE_UINT, TYPE_BOOLEAN, TYPE_LONG,
diff --git a/tests/test_properties.py b/tests/test_properties.py
index ec5df0ca..0092b7ff 100644
--- a/tests/test_properties.py
+++ b/tests/test_properties.py
@@ -746,6 +746,9 @@ class TestProperty(unittest.TestCase):
 
         PropertyObjectSubclass(obj=ObjectSubclass())
 
+    def test_generic_instance_property(self):
+        GObject.Property(type=Gio.ListStore[Gio.File])
+
     def test_property_subclass(self):
         # test for #470718
         class A(GObject.GObject):