QQuickStates: Handle more types as result of when

When calling QQmlBinding::evaluate(), we get a generic QVariant back,
and no conversions from the evaluation result to bool are done at that
point. Consequently, we would need to mirror the engines conversion from
arbitrary values to bool.
Doing that manually is rather fragile, so we instead use the QMetaType
based overload, which already takes care of the conversion. That
requires making the overload public.
As qmlsc is already using that overload from within evaluate, it was not
affected by the  bug.

Fixes: QTBUG-108024
Pick-to: 6.2 6.4 6.5
Change-Id: I3d5ee8f886ea6ada44fc8182300f3472cb1efc3c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

Author: Inkane

src/qml/qml/qqmlbinding_p.h

@@ -79,6 +79,10 @@ class Q_QML_PRIVATE_EXPORT QQmlBinding : public QQmlJavaScriptExpression,
     };
 
     QVariant evaluate();
+    bool evaluate(void *result, QMetaType type)
+    {
+        return QQmlJavaScriptExpression::evaluate(&result, &type, 0);
+    }
 
     void expressionChanged() override;
 
@@ -116,10 +120,6 @@ class Q_QML_PRIVATE_EXPORT QQmlBinding : public QQmlJavaScriptExpression,
                    QQmlPropertyData::WriteFlags flags);
 
     QV4::ReturnedValue evaluate(bool *isUndefined);
-    bool evaluate(void *result, QMetaType type)
-    {
-        return QQmlJavaScriptExpression::evaluate(&result, &type, 0);
-    }
 
 private:
     static QQmlBinding *newBinding(const QQmlPropertyData *property);

src/quick/util/qquickstategroup.cpp

@@ -353,11 +353,10 @@ bool QQuickStateGroupPrivate::updateAutoState()
                 if (abstractBinding && abstractBinding->kind() == QQmlAbstractBinding::QmlBinding) {
                     QQmlBinding *binding = static_cast<QQmlBinding *>(abstractBinding);
                     if (binding->hasValidContext()) {
-                        QVariant evalResult = binding->evaluate();
-                        if (evalResult.metaType() == QMetaType::fromType<QJSValue>())
-                            whenValue = evalResult.value<QJSValue>().toBool();
-                        else
-                            whenValue = evalResult.toBool();
+                        const auto boolType = QMetaType::fromType<bool>();
+                        const bool isUndefined = !binding->evaluate(&whenValue, boolType);
+                        if (isUndefined)
+                            whenValue = false;
                     }
                 }
 

tests/auto/quick/qquickstates/data/jsValueWhen2.qml

@@ -0,0 +1,20 @@
+import QtQuick 2.15
+
+Item {
+    id: root
+    property var prop: null
+    property bool works: false
+    states: [
+        State {
+            name: "mystate"
+            when: root.prop
+            PropertyChanges {
+                target: root
+                works: "works"
+            }
+        }
+    ]
+    Component.onCompleted: root.prop = Qt.createQmlObject(
+        "import QtQml 2.15\nQtObject {}",
+        root, "dynamicSnippet")
+}

tests/auto/quick/qquickstates/tst_qquickstates.cpp

@@ -175,6 +175,7 @@ private slots:
     void revertListMemoryLeak();
     void duplicateStateName();
     void trivialWhen();
+    void jsValueWhen_data();
     void jsValueWhen();
     void noStateOsciallation();
     void parentChangeCorrectReversal();
@@ -1695,11 +1696,20 @@ void tst_qquickstates::trivialWhen()
     QVERIFY(root);
 }
 
+
+void tst_qquickstates::jsValueWhen_data()
+{
+    QTest::addColumn<QByteArray>("fileName");
+    QTest::addRow("jsObject") << QByteArray("jsValueWhen.qml");
+    QTest::addRow("qmlObject") << QByteArray("jsValueWhen2.qml");
+}
+
 void tst_qquickstates::jsValueWhen()
 {
+    QFETCH(QByteArray, fileName);
     QQmlEngine engine;
 
-    QQmlComponent c(&engine, testFileUrl("jsValueWhen.qml"));
+    QQmlComponent c(&engine, testFileUrl(fileName.constData()));
     QScopedPointer<QObject> root(c.create());
     QVERIFY(root);
     QVERIFY(root->property("works").toBool());