QmlCompiler: Implement resetting of properties

We piggy-back on the mechanism used to handle shadowable properties and
pass the value as QVariant. QVariant can hold undefined and the lookup
functions know how to handle it.

Pick-to: 6.7 6.6 6.5 6.2
Fixes: QTBUG-120512
Change-Id: I9bca4940256c82bdcf5540b956600eb420be363e
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

4 files changed, 79 insertions, 0 deletions

diff --git a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
index c82cacd089..67d8962983 100644
--- a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
+++ b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
@@ -17,6 +17,7 @@ set(cpp_sources
     multiforeign.h
     objectwithmethod.h
     person.cpp person.h
+    resettable.h
     sequenceToIterable.h
     sequencetypeexample.cpp sequencetypeexample.h
     state.h
@@ -219,6 +220,7 @@ set(qml_files
     registerPropagation.qml
     registerelimination.qml
     renameAdjust.qml
+    resettable.qml
     returnAfterReject.qml
     revisions.qml
     scopeIdLookup.qml
diff --git a/tests/auto/qml/qmlcppcodegen/data/resettable.h b/tests/auto/qml/qmlcppcodegen/data/resettable.h
new file mode 100644
index 0000000000..129ef36ef4
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/resettable.h
@@ -0,0 +1,39 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#ifndef RESETTABLE_H
+#define RESETTABLE_H
+
+#include <QtCore/qobject.h>
+#include <QtQml/qqml.h>
+
+class ResettableProperty : public QObject
+{
+    Q_OBJECT
+    QML_NAMED_ELEMENT(Resettable)
+    Q_PROPERTY(qreal value READ value WRITE setValue RESET resetValue NOTIFY valueChanged FINAL)
+    Q_PROPERTY(qreal shadowable READ shadowable CONSTANT)
+
+public:
+    explicit ResettableProperty(QObject *parent = nullptr) : QObject(parent) {}
+    qreal value() const { return m_value; }
+    qreal shadowable() const { return 25; }
+
+public slots:
+    void resetValue() { setValue(0); }
+    void setValue(qreal value)
+    {
+        if (m_value == value)
+            return;
+        m_value = value;
+        emit valueChanged();
+    }
+
+signals:
+    void valueChanged();
+
+private:
+    qreal m_value = 0;
+};
+
+#endif // RESETTABLE_H
diff --git a/tests/auto/qml/qmlcppcodegen/data/resettable.qml b/tests/auto/qml/qmlcppcodegen/data/resettable.qml
new file mode 100644
index 0000000000..59fa31645e
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/resettable.qml
@@ -0,0 +1,15 @@
+pragma Strict
+import QtQml
+import TestTypes
+
+Resettable {
+    id: self
+    value: 999
+
+    property Resettable shadowing: Resettable {
+        property var shadowable: undefined
+    }
+
+    function doReset() { self.value = undefined }
+    function doReset2() { self.value = shadowing.shadowable }
+}
diff --git a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
index f732998647..548ad20c2b 100644
--- a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
+++ b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
@@ -8,6 +8,7 @@
 #include <data/enumproblems.h>
 #include <data/getOptionalLookup.h>
 #include <data/objectwithmethod.h>
+#include <data/resettable.h>
 #include <data/weathermoduleurl.h>
 #include <data/withlength.h>
 
@@ -186,6 +187,7 @@ private slots:
     void registerElimination();
     void registerPropagation();
     void renameAdjust();
+    void resettableProperty();
     void returnAfterReject();
     void revisions();
     void scopeIdLookup();
@@ -3837,6 +3839,27 @@ void tst_QmlCppCodegen::renameAdjust()
     QVERIFY(o);
 }
 
+void tst_QmlCppCodegen::resettableProperty()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, QUrl(u"qrc:/qt/qml/TestTypes/resettable.qml"_s));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(o);
+
+    ResettableProperty *resettable = qobject_cast<ResettableProperty *>(o.data());
+    QVERIFY(resettable);
+
+    QCOMPARE(resettable->value(), 999);
+    QMetaObject::invokeMethod(resettable, "doReset");
+    QCOMPARE(resettable->value(), 0);
+
+    resettable->setValue(82);
+    QCOMPARE(resettable->value(), 82);
+    QMetaObject::invokeMethod(resettable, "doReset2");
+    QCOMPARE(resettable->value(), 0);
+}
+
 void tst_QmlCppCodegen::returnAfterReject()
 {
     QQmlEngine engine;