Improve warning for QtQml.Binding

Print a warning if there is no property with the given
name of the specified target object, or the property
is read-only.

Change-Id: I5dc2e8330fb1ce53be396b7bf5baf13c1702d2f4
Task-number: QTBUG-39243
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

src/qml/types/qqmlbind.cpp

@@ -36,6 +36,7 @@
 #include <private/qqmlnullablevalue_p.h>
 #include <private/qqmlproperty_p.h>
 #include <private/qqmlbinding_p.h>
+#include <private/qqmlmetatype_p.h>
 
 #include <qqmlengine.h>
 #include <qqmlcontext.h>
@@ -49,6 +50,29 @@
 
 QT_BEGIN_NAMESPACE
 
+namespace {
+
+void validateProperty(QObject *target, const QString &propertyName, QObject *binding)
+{
+    if (!target)
+        return;
+
+    const QMetaObject *mo = target->metaObject();
+    const int index = mo->indexOfProperty(propertyName.toUtf8());
+    if (index == -1) {
+        qmlInfo(binding) << "Property '" << propertyName << "' does not exist on " << QQmlMetaType::prettyTypeName(target) << ".";
+        return;
+    }
+
+    const QMetaProperty mp = mo->property(index);
+    if (!mp.isWritable()) {
+        qmlInfo(binding) << "Property '" << propertyName << "' on " << QQmlMetaType::prettyTypeName(target) << " is read-only.";
+        return;
+    }
+}
+
+}
+
 class QQmlBindPrivate : public QObjectPrivate
 {
 public:
@@ -186,8 +210,10 @@ void QQmlBind::setObject(QObject *obj)
         d->when = true;
     }
     d->obj = obj;
-    if (d->componentComplete)
+    if (d->componentComplete) {
+        validateProperty(d->obj, d->propName, this);
         d->prop = QQmlProperty(d->obj, d->propName);
+    }
     eval();
 }
 
@@ -213,8 +239,10 @@ void QQmlBind::setProperty(const QString &p)
         d->when = true;
     }
     d->propName = p;
-    if (d->componentComplete)
+    if (d->componentComplete) {
+        validateProperty(d->obj, d->propName, this);
         d->prop = QQmlProperty(d->obj, d->propName);
+    }
     eval();
 }
 
@@ -253,8 +281,10 @@ void QQmlBind::componentComplete()
 {
     Q_D(QQmlBind);
     d->componentComplete = true;
-    if (!d->prop.isValid())
+    if (!d->prop.isValid()) {
+        validateProperty(d->obj, d->propName, this);
         d->prop = QQmlProperty(d->obj, d->propName);
+    }
     eval();
 }
 

tests/auto/qml/qqmlbinding/data/readonlyProperty.qml

@@ -0,0 +1,13 @@
+import QtQuick 2.0
+
+Item {
+    id: root
+
+    readonly property string name: "John"
+
+    Binding {
+        target: root
+        property: "name"
+        value: "Doe"
+    }
+}

tests/auto/qml/qqmlbinding/data/unknownProperty.qml

@@ -0,0 +1,11 @@
+import QtQuick 2.0
+
+Item {
+    id: root
+
+    Binding {
+        target: root
+        property: "unknown"
+        value: 42
+    }
+}

tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp

@@ -50,6 +50,8 @@ private slots:
     void restoreBindingWithLoop();
     void restoreBindingWithoutCrash();
     void deletedObject();
+    void warningOnUnknownProperty();
+    void warningOnReadOnlyProperty();
 
 private:
     QQmlEngine engine;
@@ -224,6 +226,38 @@ void tst_qqmlbinding::deletedObject()
     delete rect;
 }
 
+void tst_qqmlbinding::warningOnUnknownProperty()
+{
+    QQmlTestMessageHandler messageHandler;
+
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("unknownProperty.qml"));
+    QQuickItem *item = qobject_cast<QQuickItem*>(c.create());
+    QVERIFY(item);
+    delete item;
+
+    QCOMPARE(messageHandler.messages().count(), 1);
+
+    const QString expectedMessage = c.url().toString() + QLatin1String(":6:5: QML Binding: Property 'unknown' does not exist on Item.");
+    QCOMPARE(messageHandler.messages().first(), expectedMessage);
+}
+
+void tst_qqmlbinding::warningOnReadOnlyProperty()
+{
+    QQmlTestMessageHandler messageHandler;
+
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("readonlyProperty.qml"));
+    QQuickItem *item = qobject_cast<QQuickItem*>(c.create());
+    QVERIFY(item);
+    delete item;
+
+    QCOMPARE(messageHandler.messages().count(), 1);
+
+    const QString expectedMessage = c.url().toString() + QLatin1String(":8:5: QML Binding: Property 'name' on Item is read-only.");
+    QCOMPARE(messageHandler.messages().first(), expectedMessage);
+}
+
 QTEST_MAIN(tst_qqmlbinding)
 
 #include "tst_qqmlbinding.moc"