[Regression] Fix lazy binding evaluation

Commit 04774bb14c81688f86a2b31b8624bde8ebf59062 long time ago introduced the
concept of fixed order binding initialization with lazy evaluation, where a bit
is reserved for each binding that indicates whether it's been initialized the
first time or not. When reading a property on a QObject, we'd check if the
corresponding binding for the property has been initialized or not and flush
(i.e. execute) the binding if necessary.

As part of the V4/V8 clean-up, commit 1eb41200948ab414f1c47d93123b41c547a993df
removed the StoreV8Binding instruction, which made the call for setting the
this-binding-is-not-evaluated-yet bit. Nowadays we only use StoreBinding, for
which this optimization was never implemented (and not needed really). Now that
we have a unified JS code path, we need to set the pending binding bit and also
make sure that we call flushPendingBinding for any JS side property access
(accelerated or not).

Also flushPendingBindingImpl had two bugs:

   * In an attempt of trying to find the binding to flush, it could happen that
     we'd try to flush a previously destroyed binding (m_mePtr is null), so
     the b variable would remain the first binding in the object and we'd flush
     the wrong one (instead of none). Added a missing check to verify that the
     property index matches.
   * Also resetting the mePtr must be done through clear(), to ensure that the
     pointer in bindValues in the VME is also cleared, to avoid re-enabling the
     same binding again in complete();

Task-number: QTBUG-36441

Change-Id: Icdb0c8fb036051fd5d6c4d33b10cd0c0ed9a9d5c
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

6 files changed, 43 insertions, 4 deletions

diff --git a/src/qml/jsruntime/qv4qobjectwrapper.cpp b/src/qml/jsruntime/qv4qobjectwrapper.cpp
index 61f92a0f5c..cd0c81846c 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper.cpp
+++ b/src/qml/jsruntime/qv4qobjectwrapper.cpp
@@ -317,7 +317,6 @@ ReturnedValue QObjectWrapper::getQmlProperty(ExecutionContext *ctx, QQmlContextD
         return QV4::Object::get(this, name, hasProperty);
     }
 
-    QQmlData::flushPendingBinding(m_object, result->coreIndex);
     QQmlData *ddata = QQmlData::get(m_object, false);
 
     if (revisionMode == QV4::QObjectWrapper::CheckRevision && result->hasRevision()) {
@@ -338,6 +337,8 @@ ReturnedValue QObjectWrapper::getProperty(QObject *object, ExecutionContext *ctx
 {
     QV4::Scope scope(ctx);
 
+    QQmlData::flushPendingBinding(object, property->coreIndex);
+
     if (property->isFunction() && !property->isVarProperty()) {
         if (property->isVMEFunction()) {
             QQmlVMEMetaObject *vmemo = QQmlVMEMetaObject::get(object);
diff --git a/src/qml/qml/qqmlengine.cpp b/src/qml/qml/qqmlengine.cpp
index f8e5ad5874..acc66c8ce5 100644
--- a/src/qml/qml/qqmlengine.cpp
+++ b/src/qml/qml/qqmlengine.cpp
@@ -777,8 +777,8 @@ void QQmlData::flushPendingBindingImpl(int coreIndex)
     while (b && *b->m_mePtr && b->propertyIndex() != coreIndex)
         b = b->nextBinding();
 
-    if (b) {
-        b->m_mePtr = 0;
+    if (b && b->propertyIndex() == coreIndex) {
+        b->clear();
         b->setEnabled(true, QQmlPropertyPrivate::BypassInterceptor |
                             QQmlPropertyPrivate::DontRemoveBinding);
     }
diff --git a/src/qml/qml/qqmlvme.cpp b/src/qml/qml/qqmlvme.cpp
index 1881b554ed..dfc184b9f7 100644
--- a/src/qml/qml/qqmlvme.cpp
+++ b/src/qml/qml/qqmlvme.cpp
@@ -881,6 +881,12 @@ QObject *QQmlVME::run(QList<QQmlError> *errors,
                 CLEAN_PROPERTY(target, QDPP::bindingIndex(instr.property));
 
                 bind->addToObject();
+
+                if (!instr.property.isValueTypeVirtual()) {
+                    QQmlData *data = QQmlData::get(target);
+                    Q_ASSERT(data);
+                    data->setPendingBindingBit(target, instr.property.coreIndex);
+                }
             }
         QML_END_INSTR(StoreBinding)
 
diff --git a/tests/auto/qml/qqmlecmascript/data/LazyBindingComponent.qml b/tests/auto/qml/qqmlecmascript/data/LazyBindingComponent.qml
new file mode 100644
index 0000000000..81cb56f0e5
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/LazyBindingComponent.qml
@@ -0,0 +1,13 @@
+import QtQuick 2.0
+
+Item
+{
+    property int someInt: 4
+    property var variantArray: [1, 2]
+    property int arrayLength: 0
+
+    onSomeIntChanged:
+    {
+        arrayLength = variantArray.length
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/data/lazyBindingEvaluation.qml b/tests/auto/qml/qqmlecmascript/data/lazyBindingEvaluation.qml
new file mode 100644
index 0000000000..2f55ff0709
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/lazyBindingEvaluation.qml
@@ -0,0 +1,6 @@
+import QtQuick 2.1
+
+LazyBindingComponent
+{
+    someInt: 5
+}
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index c45750caac..3f412ee6d4 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -321,6 +321,7 @@ private slots:
     void qtbug_34792();
     void noCaptureWhenWritingProperty();
     void singletonWithEnum();
+    void lazyBindingEvaluation();
 
 private:
 //    static void propertyVarWeakRefCallback(v8::Persistent<v8::Value> object, void* parameter);
@@ -667,7 +668,7 @@ void tst_qqmlecmascript::methods()
 void tst_qqmlecmascript::bindingLoop()
 {
     QQmlComponent component(&engine, testFileUrl("bindingLoop.qml"));
-    QString warning = component.url().toString() + ":5:9: QML MyQmlObject: Binding loop detected for property \"stringProperty\"";
+    QString warning = component.url().toString() + ":9:9: QML MyQmlObject: Binding loop detected for property \"stringProperty\"";
     QTest::ignoreMessage(QtWarningMsg, warning.toLatin1().constData());
     QObject *object = component.create();
     QVERIFY(object != 0);
@@ -7520,6 +7521,18 @@ void tst_qqmlecmascript::singletonWithEnum()
     QCOMPARE(prop.toInt(), int(SingletonWithEnum::TestValue));
 }
 
+void tst_qqmlecmascript::lazyBindingEvaluation()
+{
+   QQmlComponent component(&engine, testFileUrl("lazyBindingEvaluation.qml"));
+   QScopedPointer<QObject> obj(component.create());
+   if (obj.isNull())
+       qDebug() << component.errors().first().toString();
+   QVERIFY(!obj.isNull());
+   QVariant prop = obj->property("arrayLength");
+   QVERIFY(prop.type() == QVariant::Int);
+   QCOMPARE(prop.toInt(), 2);
+}
+
 QTEST_MAIN(tst_qqmlecmascript)
 
 #include "tst_qqmlecmascript.moc"