Make property interceptors work on alias properties again

Fixes a regression introduced by change
01c0c0963794f4dd8c3601e8340cc3dc4dec41bd, where interceptors
wouldn't work correctly on alias properties.

This required some refactoring and splitting out the interceptor
handling from the VMEMO into it's own class, as we are now
installing bindings directly on the target property of an alias and
not on the alias anymore.

We now resolve the target property inside the QML object creator
and install a interceptor metaobject on the target if required where
we can then register the interceptor.

Change-Id: I3ebc8f492ce5dcab7acf901711b47336d5182ffa
Task-number: QTBUG-49072
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

3 files changed, 75 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickbehaviors/data/Accelerator.qml b/tests/auto/quick/qquickbehaviors/data/Accelerator.qml
new file mode 100644
index 0000000000..a2b5146c3f
--- /dev/null
+++ b/tests/auto/quick/qquickbehaviors/data/Accelerator.qml
@@ -0,0 +1,18 @@
+import QtQuick 2.3
+
+Rectangle {
+    property alias value: range.width
+    color: "yellow"
+    Text {
+        text: 'value: ' + value
+    }
+
+    Rectangle {
+        id: range
+        objectName: "range"
+        color: "red"
+        width: 0
+        height: 5
+        anchors.bottom: parent.bottom
+    }
+}
diff --git a/tests/auto/quick/qquickbehaviors/data/aliased.qml b/tests/auto/quick/qquickbehaviors/data/aliased.qml
new file mode 100644
index 0000000000..e65e035d83
--- /dev/null
+++ b/tests/auto/quick/qquickbehaviors/data/aliased.qml
@@ -0,0 +1,39 @@
+import QtQuick 2.3
+
+Rectangle {
+    width: 400
+    height: 400
+    id: rect
+    property bool accelerating : false
+    
+    Text {
+        anchors.centerIn: parent
+        text: "Press anywere to accelerate"
+    }
+
+    Accelerator {
+        id: acc
+        objectName: "acc"
+        anchors.fill: parent
+        value: accelerating ? 400 : 0
+        Behavior on value {
+            NumberAnimation {
+                duration: 500
+            }
+        }
+    }
+
+    MouseArea {
+        id: clicker
+        anchors.fill: parent
+    }
+
+    states: State {
+        name: "moved"
+        when: clicker.pressed
+        PropertyChanges {
+            target: rect
+            accelerating: true
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickbehaviors/tst_qquickbehaviors.cpp b/tests/auto/quick/qquickbehaviors/tst_qquickbehaviors.cpp
index 643bed4376..635958314f 100644
--- a/tests/auto/quick/qquickbehaviors/tst_qquickbehaviors.cpp
+++ b/tests/auto/quick/qquickbehaviors/tst_qquickbehaviors.cpp
@@ -76,6 +76,7 @@ private slots:
     void multipleChangesToValueType();
     void currentValue();
     void disabledWriteWhileRunning();
+    void aliasedProperty();
 };
 
 void tst_qquickbehaviors::simpleBehavior()
@@ -576,6 +577,23 @@ void tst_qquickbehaviors::disabledWriteWhileRunning()
     }
 }
 
+void tst_qquickbehaviors::aliasedProperty()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("aliased.qml"));
+    QScopedPointer<QQuickRectangle> rect(qobject_cast<QQuickRectangle*>(c.create()));
+    QVERIFY2(!rect.isNull(), qPrintable(c.errorString()));
+
+    QQuickItemPrivate::get(rect.data())->setState("moved");
+    QScopedPointer<QQuickRectangle> acc(qobject_cast<QQuickRectangle*>(rect->findChild<QQuickRectangle*>("acc")));
+    QScopedPointer<QQuickRectangle> range(qobject_cast<QQuickRectangle*>(acc->findChild<QQuickRectangle*>("range")));
+    QTRY_VERIFY(acc->property("value").toDouble() > 0);
+    QTRY_VERIFY(range->width() > 0);
+    QTRY_VERIFY(acc->property("value").toDouble() < 400);
+    QTRY_VERIFY(range->width() < 400);
+    //i.e. the behavior has been triggered
+}
+
 QTEST_MAIN(tst_qquickbehaviors)
 
 #include "tst_qquickbehaviors.moc"