QmlCompiler: Error out when writing to property of unknown type

Otherwise we get a conversion to unknown and that is bad.

Fixes: QTBUG-117361
Change-Id: Iead1ddd21b692ed9fb9923dccdfa5bd01dc9d467
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Nicolas Fella <nicolas.fella@kdab.com>
(cherry picked from commit d0c7f46b4090010fbb8ebfd6ce200d8bb3dbaadb)
(cherry picked from commit d5ab133e2ee2e9ec781179baefde6404c93885b1)
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>

2 files changed, 14 insertions, 0 deletions

diff --git a/src/qmlcompiler/qqmljstypepropagator.cpp b/src/qmlcompiler/qqmljstypepropagator.cpp
index 24bc75c0dc..7aef48d2d1 100644
--- a/src/qmlcompiler/qqmljstypepropagator.cpp
+++ b/src/qmlcompiler/qqmljstypepropagator.cpp
@@ -899,6 +899,12 @@ void QQmlJSTypePropagator::generate_StoreProperty(int nameIndex, int base)
         return;
     }
 
+    if (property.storedType().isNull()) {
+        setError(u"Cannot determine type for property %1 of type %2"_s.arg(
+                propertyName, callBase.descriptiveName()));
+        return;
+    }
+
     if (!property.isWritable() && !property.storedType()->isListProperty()) {
         setError(u"Can't assign to read-only property %1"_s.arg(propertyName));
 
diff --git a/tests/auto/qml/qmlcppcodegen/data/failures.qml b/tests/auto/qml/qmlcppcodegen/data/failures.qml
index e802a43302..ee3eaee359 100644
--- a/tests/auto/qml/qmlcppcodegen/data/failures.qml
+++ b/tests/auto/qml/qmlcppcodegen/data/failures.qml
@@ -9,6 +9,7 @@ QtObject {
     property string attachedForNasty: Nasty.objectName
 
     property Nasty nasty: Nasty {
+        id: theNasty
         objectName: Component.objectName
     }
 
@@ -70,4 +71,11 @@ QtObject {
     function readTracks(metadataList : list<badType>): int {
         return metadataList.length
     }
+
+    property alias selfself: self
+    property alias nastyBad: theNasty.bad
+    function writeToUnknown() : int {
+        self.selfself.nastyBad = undefined;
+        return 5;
+    }
 }