Fix interface handling in bindings

If a type had a property with an interface type, we did not support the
case where the assigned binding value is convertible to the interface.

This is now fixed by adding a last new check to QQmlPrivate::write

Fixes: QTBUG-78721
Change-Id: I0b85fbfdf8561ba43610ac343001ae380287a674
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmlproperty/data/interfaceBinding.qml b/tests/auto/qml/qqmlproperty/data/interfaceBinding.qml
new file mode 100644
index 0000000000..4e72a75f42
--- /dev/null
+++ b/tests/auto/qml/qqmlproperty/data/interfaceBinding.qml
@@ -0,0 +1,27 @@
+import QtQuick 2.12
+import io.qt.bugreports 1.0
+Item {
+    InterfaceConsumer {
+        objectName: "a1"
+        i: A {
+            property int i: 42
+        }
+    }
+
+    InterfaceConsumer {
+        objectName: "a2"
+        property A a: A {
+            property int i: 43
+        }
+        i: a
+    }
+
+    InterfaceConsumer {
+        objectName: "a3"
+        property A a: A {
+            id : aa
+            property int i: 44
+        }
+        i: aa
+    }
+}