Fix QProperty property interaction with aliases

With this change, an alias of a bindable property is also bindable, and
shares its bindable interface with the target.

Moreover, the logic in QQmlTypeCompiler is adjusted so that a change
handler of an alias uses the bindable interface if possible, instead of
connecting to the alias' change signal. That would never be emitted if
the target is a QProperty without a notify signal.

Alias properties still have a change signal, but those never get
emitted.

Change-Id: I857dfdbe51048a2b604ad632982e7f4adac6b907
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

5 files changed, 24 insertions, 5 deletions

diff --git a/src/qml/qml/qqmlobjectcreator.cpp b/src/qml/qml/qqmlobjectcreator.cpp
index 45c9400934..43c639ce8d 100644
--- a/src/qml/qml/qqmlobjectcreator.cpp
+++ b/src/qml/qml/qqmlobjectcreator.cpp
@@ -890,10 +890,24 @@ bool QQmlObjectCreator::setPropertyBinding(const QQmlPropertyData *bindingProper
                         _scopeObject, runtimeFunction, currentQmlContext());
 
             if (bindingProperty->isBindable()) {
+                auto target = _bindingTarget;
+                if (bindingProperty->isAlias()) {
+                    // If the property is an alias, we cannot obtain the bindable interface directly with qt_metacall
+                    // so instead, we resolve the alias to obtain the actual target
+                    // This should be faster than doing a detour through the metaobject of the target, and relying on
+                    // QMetaObject::metacall doing the correct resolution
+                    QQmlPropertyIndex originalIndex(bindingProperty->coreIndex(), _valueTypeProperty ? _valueTypeProperty->coreIndex() : -1);
+                    QQmlPropertyIndex propIndex;
+                    QQmlPropertyPrivate::findAliasTarget(target, originalIndex, &target, &propIndex);
+                    QQmlData *data = QQmlData::get(target);
+                    Q_ASSERT(data && data->propertyCache);
+                    bindingProperty = data->propertyCache->property(propIndex.coreIndex());
+                }
                 auto &observer = QQmlData::get(_scopeObject)->propertyObservers.emplace_back(expr);
                 QUntypedBindable bindable;
                 void *argv[] = { &bindable };
-                _bindingTarget->qt_metacall(QMetaObject::BindableProperty, bindingProperty->coreIndex(), argv);
+                target->qt_metacall(QMetaObject::BindableProperty, bindingProperty->coreIndex(), argv);
+                Q_ASSERT(bindable.isValid());
                 bindable.observe(&observer);
             } else {
                 QQmlBoundSignal *bs = new QQmlBoundSignal(_bindingTarget, signalIndex, _scopeObject, engine);
diff --git a/src/qml/qml/qqmlpropertycache.cpp b/src/qml/qml/qqmlpropertycache.cpp
index 3c6c0c82de..4f557527c9 100644
--- a/src/qml/qml/qqmlpropertycache.cpp
+++ b/src/qml/qml/qqmlpropertycache.cpp
@@ -1147,6 +1147,7 @@ void QQmlPropertyCache::toMetaObjectBuilder(QMetaObjectBuilder &builder)
         property.setReadable(true);
         property.setWritable(data->isWritable());
         property.setResettable(data->isResettable());
+        property.setBindable(data->isBindable());
     }
 
     for (int ii = 0; ii < methods.count(); ++ii) {
diff --git a/src/qml/qml/qqmlpropertycachecreator_p.h b/src/qml/qml/qqmlpropertycachecreator_p.h
index 626b274c2f..21551db5c4 100644
--- a/src/qml/qml/qqmlpropertycachecreator_p.h
+++ b/src/qml/qml/qqmlpropertycachecreator_p.h
@@ -785,6 +785,7 @@ inline QQmlError QQmlPropertyCacheAliasCreator<ObjectContainer>::propertyDataFor
     *type = 0;
     bool writable = false;
     bool resettable = false;
+    bool bindable = false;
 
     propertyFlags->setIsAlias(true);
 
@@ -861,13 +862,14 @@ inline QQmlError QQmlPropertyCacheAliasCreator<ObjectContainer>::propertyDataFor
             *type = targetProperty->propType();
             writable = targetProperty->isWritable();
             resettable = targetProperty->isResettable();
-
+            bindable = targetProperty->isBindable();
         } else {
             // value type or primitive type or enum
             *type = targetProperty->propType();
 
             writable = targetProperty->isWritable();
             resettable = targetProperty->isResettable();
+            bindable = targetProperty->isBindable();
 
             if (valueTypeIndex != -1) {
                 const QMetaObject *valueTypeMetaObject = QQmlValueTypeFactory::metaObjectForMetaType(*type);
@@ -891,6 +893,7 @@ inline QQmlError QQmlPropertyCacheAliasCreator<ObjectContainer>::propertyDataFor
 
     propertyFlags->setIsWritable(!(alias.flags & QV4::CompiledData::Alias::IsReadOnly) && writable);
     propertyFlags->setIsResettable(resettable);
+    propertyFlags->setIsBindable(bindable);
     return QQmlError();
 }
 
diff --git a/src/qml/qml/qqmltypecompiler.cpp b/src/qml/qml/qqmltypecompiler.cpp
index ca8a24439b..eb3b0e43ac 100644
--- a/src/qml/qml/qqmltypecompiler.cpp
+++ b/src/qml/qml/qqmltypecompiler.cpp
@@ -382,7 +382,8 @@ bool SignalHandlerConverter::convertSignalHandlerExpressionsToFunctionDeclaratio
         QString finalSignalHandlerPropertyName = signalNameCandidate;
         uint flags = QV4::CompiledData::Binding::IsSignalHandlerExpression;
 
-        if (signal) {
+        const bool isPropertyObserver = !signalPropertyData && qPropertyData && qPropertyData->isBindable();
+        if (signal && !(qPropertyData && qPropertyData->isAlias() && isPropertyObserver)) {
             int sigIndex = propertyCache->methodIndexToSignalIndex(signal->coreIndex());
             sigIndex = propertyCache->originalClone(sigIndex);
 
@@ -400,7 +401,7 @@ bool SignalHandlerConverter::convertSignalHandlerExpressionsToFunctionDeclaratio
                 }
                 parameters += param;
             }
-        } else if (!signalPropertyData && qPropertyData && qPropertyData->isBindable()) {
+        } else if (isPropertyObserver) {
             finalSignalHandlerPropertyName = qPropertyName;
             flags = QV4::CompiledData::Binding::IsPropertyObserver;
         } else {
diff --git a/src/qml/qml/qqmlvmemetaobject.cpp b/src/qml/qml/qqmlvmemetaobject.cpp
index 2d0f131477..6919c6dba3 100644
--- a/src/qml/qml/qqmlvmemetaobject.cpp
+++ b/src/qml/qml/qqmlvmemetaobject.cpp
@@ -687,7 +687,7 @@ int QQmlVMEMetaObject::metaCall(QObject *o, QMetaObject::Call c, int _id, void *
     const int signalCount = compiledObject ? int(compiledObject->nSignals) : 0;
     const int methodCount = compiledObject ? int(compiledObject->nFunctions) : 0;
 
-    if (c == QMetaObject::ReadProperty || c == QMetaObject::WriteProperty || c == QMetaObject::ResetProperty) {
+    if (c == QMetaObject::ReadProperty || c == QMetaObject::WriteProperty || c == QMetaObject::ResetProperty || c == QMetaObject::BindableProperty) {
         if (id >= propOffset()) {
             id -= propOffset();