QmlBind: support bindable properties

This patch ensures that the QML Binding element can also save and restore
C++ bindings. Should QQuickItem's x and y property be ported to the new
property system, we'd need new test cases to verify that "old-style"
bindings are still handled correctly. This task is however left for the
change porting the properties.

Task-number: QTBUG-90493
Change-Id: I506ffa1060ff32a7d722214e5ccd469bdaa61ff8
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/qml/types/qqmlbind.cpp

@@ -83,7 +83,10 @@ public:
     QString propName;
     QQmlNullableValue<QJSValue> value;
     QQmlProperty prop;
-    QQmlAbstractBinding::Ptr prevBind;
+    union {
+        QQmlAbstractBinding::Ptr prevBind;
+        QUntypedPropertyBinding prevPropertyBinding;
+    };
     QV4::PersistentValue v4Value;
     QVariant prevValue;
     bool prevIsVariant:1;
@@ -96,6 +99,7 @@ public:
 
     void validate(QObject *binding) const;
     void clearPrev();
+    bool prevBindingSet() const;
 };
 
 void QQmlBindPrivate::validate(QObject *binding) const
@@ -444,12 +448,23 @@ void QQmlBind::prepareEval()
 
 void QQmlBindPrivate::clearPrev()
 {
-    prevBind = nullptr;
+    if (prop.property().isBindable())
+        prevPropertyBinding = {};
+    else
+        prevBind = nullptr;
     v4Value.clear();
     prevValue.clear();
     prevIsVariant = false;
 }
 
+bool QQmlBindPrivate::prevBindingSet() const
+{
+    if (prop.property().isBindable())
+        return !prevPropertyBinding.isNull();
+    else
+        return prevBind;
+}
+
 void QQmlBind::eval()
 {
     Q_D(QQmlBind);
@@ -460,11 +475,18 @@ void QQmlBind::eval()
     if (d->when.isValid()) {
         if (!d->when) {
             //restore any previous binding
-            if (d->prevBind) {
+            if (d->prevBindingSet()) {
                 if (d->restoreBinding) {
-                    QQmlAbstractBinding::Ptr p = d->prevBind;
-                    d->clearPrev(); // Do that before setBinding(), as setBinding() may recurse.
-                    QQmlPropertyPrivate::setBinding(p.data());
+                    QMetaProperty metaProp = d->prop.property();
+                    if (metaProp.isBindable()) {
+                        auto prevBinding = d->prevPropertyBinding;
+                        d->clearPrev(); // Do that before setBinding(), as setBinding() may recurse.
+                        metaProp.bindable(d->prop.object()).setBinding(prevBinding);
+                    } else {
+                        QQmlAbstractBinding::Ptr p = d->prevBind;
+                        d->clearPrev(); // Do that before setBinding(), as setBinding() may recurse.
+                        QQmlPropertyPrivate::setBinding(p.data());
+                    }
                 }
             } else if (!d->v4Value.isEmpty()) {
                 if (d->restoreValue) {
@@ -484,11 +506,18 @@ void QQmlBind::eval()
         }
 
         //save any set binding for restoration
-        if (!d->prevBind && d->v4Value.isEmpty() && !d->prevIsVariant) {
+        if (!d->prevBindingSet() && d->v4Value.isEmpty() && !d->prevIsVariant) {
             // try binding first
-            d->prevBind = QQmlPropertyPrivate::binding(d->prop);
+            d->prop.property().isBindable();
+            QMetaProperty metaProp = d->prop.property();
+            if (metaProp.isBindable()) {
+                QUntypedBindable bindable = d->prop.property().bindable(d->prop.object());
+                d->prevPropertyBinding = bindable.takeBinding();
+            } else {
+                d->prevBind = QQmlPropertyPrivate::binding(d->prop);
+            }
 
-            if (!d->prevBind) { // nope, try a V4 value next
+            if (!d->prevBindingSet()) { // nope, try a V4 value next
                 auto propPriv = QQmlPropertyPrivate::get(d->prop);
                 auto propData = propPriv->core;
                 if (!propPriv->valueTypeData.isValid() && propData.isVarProperty()) {
@@ -503,6 +532,8 @@ void QQmlBind::eval()
             }
         }
 
+        // NOTE: removeBinding has no effect on QProperty classes, but
+        // we already used takeBinding to remove it
         QQmlPropertyPrivate::removeBinding(d->prop);
     }
 

tests/auto/qml/qqmlbinding/CMakeLists.txt

@@ -14,6 +14,7 @@ qt_internal_add_test(tst_qqmlbinding
     SOURCES
         ../../shared/util.cpp ../../shared/util.h
         tst_qqmlbinding.cpp
+        WithBindableProperties.h
     INCLUDE_DIRECTORIES
         ../../shared
     PUBLIC_LIBRARIES
@@ -25,6 +26,14 @@ qt_internal_add_test(tst_qqmlbinding
     TESTDATA ${test_data}
 )
 
+set_target_properties(tst_qqmlbinding PROPERTIES
+    QT_QML_MODULE_URI "test"
+    QT_QML_MODULE_VERSION 1.0
+)
+
+qt6_qml_type_registration(tst_qqmlbinding)
+
+
 ## Scopes:
 #####################################################################
 

tests/auto/qml/qqmlbinding/WithBindableProperties.h

@@ -0,0 +1,55 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef WithBindableProperties_H
+#define WithBindableProperties_H
+
+#include <QObject>
+#include <qqml.h>
+
+
+class WithBindableProperties : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+
+    Q_PROPERTY(int a READ a WRITE setA BINDABLE bindableA)
+    Q_PROPERTY(int b READ b WRITE setB BINDABLE bindableB)
+
+public:
+    QProperty<int> m_a;
+    QProperty<int> m_b;
+    int a() {return m_a;}
+    int b() {return m_b;}
+    void setA(int val) {m_a = val;}
+    void setB(int val) {m_b = val;}
+    QBindable<int> bindableA() {return QBindable<int>(&m_a); }
+    QBindable<int> bindableB() {return QBindable<int>(&m_b); }
+};
+
+#endif
+

tests/auto/qml/qqmlbinding/data/restoreBinding5.qml

@@ -0,0 +1,24 @@
+import QtQuick 2.0
+import test 1
+
+Rectangle {
+    width: 400
+    height: 400
+
+    WithBindableProperties {
+        id: myItem
+        objectName:  "myItem"
+        a: 100 - myItem.b
+
+        Binding on a {
+            when: myItem.b > 50
+            value: myItem.b
+        }
+
+        /*NumberAnimation on y {
+            loops: Animation.Infinite
+            to: 100
+            duration: 1000
+        }*/
+    }
+}

tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp

@@ -31,6 +31,7 @@
 #include <private/qqmlbind_p.h>
 #include <QtQuick/private/qquickrectangle_p.h>
 #include "../../shared/util.h"
+#include "WithBindableProperties.h"
 
 class tst_qqmlbinding : public QQmlDataTest
 {
@@ -42,6 +43,7 @@ private slots:
     void binding();
     void whenAfterValue();
     void restoreBinding();
+    void restoreBindingBindablePorperty();
     void restoreBindingValue();
     void restoreBindingVarValue();
     void restoreBindingJSValue();
@@ -134,6 +136,34 @@ void tst_qqmlbinding::restoreBinding()
     QCOMPARE(myItem->x(), qreal(100-49));
 }
 
+void tst_qqmlbinding::restoreBindingBindablePorperty()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("restoreBinding5.qml"));
+    QScopedPointer<QQuickRectangle> rect { qobject_cast<QQuickRectangle*>(c.create()) };
+    QVERIFY2(rect, qPrintable(c.errorString()));
+
+    auto *myItem = rect->findChild<WithBindableProperties*>("myItem");
+    QVERIFY(myItem != nullptr);
+
+    myItem->setB(25);
+    QCOMPARE(myItem->a(), qreal(100-25));
+
+    myItem->setB(13);
+    QCOMPARE(myItem->a(), qreal(100-13));
+
+    //Binding takes effect
+    myItem->setB(51);
+    QCOMPARE(myItem->a(), qreal(51));
+
+    myItem->setB(88);
+    QCOMPARE(myItem->a(), qreal(88));
+
+    //original binding restored
+    myItem->setB(49);
+    QCOMPARE(myItem->a(), qreal(100-49));
+}
+
 void tst_qqmlbinding::restoreBindingValue()
 {
     QQmlEngine engine;