Improve support for var properties

This commit changes the semantics of function assignment in QML.
Previously, function assignment was interpreted as binding assignment.
Now, function assignment is interpreted as function assignment, and
therefore fails for all property types other than "var" properties.

To support imperative binding assignment, a new function was added to
the Qt object: Qt.binding(function) which takes a single function
parameter and returns a function object which will be interpreted as
an assignable binding expression by the QML engine.

Finally, this commit also slightly changes the semantics of var
properties in that the "special" JavaScript values of null and
undefined may be assigned to var properties, rather than being
interpreted as reset requests.

Task-number: QTBUG-21842
Change-Id: Iee99a878b9badf0fb76e983da7ebfa493f55ceb5
Reviewed-by: Matthew Vogt <matthew.vogt@nokia.com>

3 files changed, 37 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.2.qml b/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.2.qml
new file mode 100644
index 0000000000..0da717ba5c
--- /dev/null
+++ b/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.2.qml
@@ -0,0 +1,12 @@
+import QtQuick 2.0
+import Test 1.0
+
+MyTypeObject {
+    property int value: 10
+    rect.y: Qt.binding(function() { return value; }); // error.
+
+    Component.onCompleted: {
+        rect.x = 5;
+        rect.x = (function() { return value; }); // error.
+    }
+}
diff --git a/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.qml b/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.qml
index a65218669b..9b10803649 100644
--- a/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.qml
+++ b/tests/auto/qml/qqmlvaluetypes/data/bindingAssignment.qml
@@ -1,7 +1,12 @@
+import QtQuick 2.0
 import Test 1.0
 
 MyTypeObject {
     property int value: 10
 
     rect.x: value
+
+    Component.onCompleted: {
+        rect.y = Qt.binding(function() { return value + 5; });
+    }
 }
diff --git a/tests/auto/qml/qqmlvaluetypes/tst_qqmlvaluetypes.cpp b/tests/auto/qml/qqmlvaluetypes/tst_qqmlvaluetypes.cpp
index 0aa223e733..c37a42fee5 100644
--- a/tests/auto/qml/qqmlvaluetypes/tst_qqmlvaluetypes.cpp
+++ b/tests/auto/qml/qqmlvaluetypes/tst_qqmlvaluetypes.cpp
@@ -871,17 +871,37 @@ void tst_qqmlvaluetypes::color()
 // Test bindings can write to value types
 void tst_qqmlvaluetypes::bindingAssignment()
 {
+    // binding declaration
+    {
     QQmlComponent component(&engine, testFileUrl("bindingAssignment.qml"));
     MyTypeObject *object = qobject_cast<MyTypeObject *>(component.create());
     QVERIFY(object != 0);
 
     QCOMPARE(object->rect().x(), 10);
+    QCOMPARE(object->rect().y(), 15);
 
     object->setProperty("value", QVariant(92));
 
     QCOMPARE(object->rect().x(), 92);
+    QCOMPARE(object->rect().y(), 97);
 
     delete object;
+    }
+
+    // function assignment should fail without crashing
+    {
+    QString warning1 = testFileUrl("bindingAssignment.2.qml").toString() + QLatin1String(":6: Invalid use of Qt.binding() in a binding declaration.");
+    QString warning2 = testFileUrl("bindingAssignment.2.qml").toString() + QLatin1String(":10: Error: Cannot assign JavaScript function to value-type property");
+    QTest::ignoreMessage(QtWarningMsg, qPrintable(warning1));
+    QTest::ignoreMessage(QtWarningMsg, qPrintable(warning2));
+    QQmlComponent component(&engine, testFileUrl("bindingAssignment.2.qml"));
+    MyTypeObject *object = qobject_cast<MyTypeObject *>(component.create());
+    QVERIFY(object != 0);
+    QCOMPARE(object->rect().x(), 5);
+    object->setProperty("value", QVariant(92));
+    QCOMPARE(object->rect().x(), 5);
+    delete object;
+    }
 }
 
 // Test bindings can read from value types