QQmlProperty: Reset the binding bit when removing a null binding

If we remove a binding we don't want any later code to restore it. This
works quite well if the binding we remove already exists.
removeFromObject() resets the binding bit and that settles it. However,
if the binding doesn't exist yet, we so far didn't reset the bit and
when the binding appeared we would still add it to the object. That was
quite wrong.

Pick-to: 6.7 6.5 6.2
Fixes: QTBUG-124553
Change-Id: I58c115d78b3701ad4e8837772261a9154b971dbb
Reviewed-by: Fabian Kosmale <[email protected]>
(cherry picked from commit c9d7620)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>

Author: ulfhermannqt

src/qml/qml/qqmlproperty.cpp

@@ -843,17 +843,21 @@ static void removeOldBinding(QObject *object, QQmlPropertyIndex index, QQmlPrope
     oldBinding = data->bindings;
 
     while (oldBinding && (oldBinding->targetPropertyIndex().coreIndex() != coreIndex ||
-                          oldBinding->targetPropertyIndex().hasValueTypeIndex()))
+                          oldBinding->targetPropertyIndex().hasValueTypeIndex())) {
         oldBinding = oldBinding->nextBinding();
+    }
 
-    if (!oldBinding)
-        return;
-
-    if (valueTypeIndex != -1 && oldBinding->kind() == QQmlAbstractBinding::ValueTypeProxy)
+    if (valueTypeIndex != -1
+            && oldBinding
+            && oldBinding->kind() == QQmlAbstractBinding::ValueTypeProxy) {
         oldBinding = static_cast<QQmlValueTypeProxyBinding *>(oldBinding.data())->binding(index);
+    }
 
-    if (!oldBinding)
+    if (!oldBinding) {
+        // Clear the binding bit so that the binding doesn't appear later for any reason
+        data->clearBindingBit(coreIndex);
         return;
+    }
 
     if (!(flags & QQmlPropertyPrivate::DontEnable))
         oldBinding->setEnabled(false, {});

tests/auto/qml/qqmllanguage/data/BindingOverrider.qml

@@ -0,0 +1,5 @@
+import QtQml 2.15
+
+SimpleWidget {
+    width: 20
+}

tests/auto/qml/qqmllanguage/data/SimpleWidget.qml

@@ -0,0 +1,25 @@
+import QtQuick 2.15
+
+Item {
+    id: outer
+
+    property real innerWidth: 0
+
+    Item {
+        id: inner
+        width: style.width
+        onWidthChanged: outer.innerWidth = width
+    }
+
+    width: inner.width
+
+    onWidthChanged: {
+        if (width !== inner.width)
+            inner.width = width // overwrite binding
+    }
+
+    QtObject {
+        id: style
+        property int width: 50
+    }
+}

tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp

@@ -464,6 +464,8 @@ private slots:
     void nestedVectors();
     void optimizedSequenceShift();
 
+    void overrideInnerBinding();
+
 private:
     QQmlEngine engine;
     QStringList defaultImportPathList;
@@ -8980,6 +8982,18 @@ void tst_qqmllanguage::optimizedSequenceShift()
     QCOMPARE(one.toInt(), 1);
 }
 
+void tst_qqmllanguage::overrideInnerBinding()
+{
+    QQmlEngine e;
+    QQmlComponent c(&e, testFileUrl("BindingOverrider.qml"));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+
+    QCOMPARE(o->property("width").toReal(), 20.0);
+    QCOMPARE(o->property("innerWidth").toReal(), 20.0);
+}
+
 QTEST_MAIN(tst_qqmllanguage)
 
 #include "tst_qqmllanguage.moc"