SignalTransition: fix binding loops

This one is a bit special, because the setter assumes that there is a
QML engine handling the object.
As a result, creating a helper object for testing binding loops is a
bit tricky. Do it by having a helper QQmlComponent based on a qml file
with a SignalTransition object as a root element.
Fix the binding loop in the setter in a usual way.

Task-number: QTBUG-116542
Pick-to: 6.6 6.5
Change-Id: Ibd22dee0619a69b52901e9fe2145fcfbd9dcf98c
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 22 insertions, 5 deletions

diff --git a/src/statemachineqml/signaltransition.cpp b/src/statemachineqml/signaltransition.cpp
index 0c16df0..311edda 100644
--- a/src/statemachineqml/signaltransition.cpp
+++ b/src/statemachineqml/signaltransition.cpp
@@ -89,10 +89,9 @@ const QJSValue& SignalTransition::signal()
 
 void SignalTransition::setSignal(const QJSValue &signal)
 {
-    if (m_signal.value().strictlyEquals(signal)) {
-        m_signal.removeBindingUnlessInWrapper();
+    m_signal.removeBindingUnlessInWrapper();
+    if (m_signal.valueBypassingBindings().strictlyEquals(signal))
         return;
-    }
 
     QV4::ExecutionEngine *jsEngine = QQmlEngine::contextForObject(this)->engine()->handle();
     QV4::Scope scope(jsEngine);
@@ -100,7 +99,7 @@ void SignalTransition::setSignal(const QJSValue &signal)
     QObject *sender;
     QMetaMethod signalMethod;
 
-    m_signal = signal;
+    m_signal.setValueBypassingBindings(signal);
     QV4::ScopedValue value(scope, QJSValuePrivate::asReturnedValue(&signal));
 
     // Did we get the "slot" that can be used to invoke the signal?
diff --git a/tests/auto/qml/qqmlstatemachine/data/signaltransitionhelper.qml b/tests/auto/qml/qqmlstatemachine/data/signaltransitionhelper.qml
new file mode 100644
index 0000000..f915cdb
--- /dev/null
+++ b/tests/auto/qml/qqmlstatemachine/data/signaltransitionhelper.qml
@@ -0,0 +1,10 @@
+// Copyright (C) 2023 The Qt Company
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+import QtQuick
+import QtQml.StateMachine
+
+SignalTransition {
+    // Do not crash on SignalTransition without signal
+    onTriggered: () => {}
+}
diff --git a/tests/auto/qml/qqmlstatemachine/tst_qqmlstatemachine.cpp b/tests/auto/qml/qqmlstatemachine/tst_qqmlstatemachine.cpp
index 81e2fb6..e9f1721 100644
--- a/tests/auto/qml/qqmlstatemachine/tst_qqmlstatemachine.cpp
+++ b/tests/auto/qml/qqmlstatemachine/tst_qqmlstatemachine.cpp
@@ -116,10 +116,18 @@ void tst_qqmlstatemachine::tst_bindings()
     QVariant signal2;
     QMetaObject::invokeMethod(obj.get(), "getSignal1", Q_RETURN_ARG(QVariant, signal1));
     QMetaObject::invokeMethod(obj.get(), "getSignal2", Q_RETURN_ARG(QVariant, signal2));
+    // The setter needs an active engine, so we use a helper component to create
+    // a helper instance for testing binding loops.
+    QQmlComponent helperComponent(&engine, testFileUrl("signaltransitionhelper.qml"));
     // QJSValue does not implement operator== so we supply own comparator
     QTestPrivate::testReadWritePropertyBasics<SignalTransition, QJSValue>(
                 *st1, signal1.value<QJSValue>(), signal2.value<QJSValue>(), "signal",
-                [](QJSValue d1, QJSValue d2) { return d1.strictlyEquals(d2); });
+                [](QJSValue d1, QJSValue d2) { return d1.strictlyEquals(d2); },
+                [](const QJSValue &val) { return QTest::toString(val); },
+                [&helperComponent]() {
+                    return std::unique_ptr<SignalTransition>(
+                        qobject_cast<SignalTransition*>(helperComponent.create()));
+                });
     if (QTest::currentTestFailed()) {
         qWarning() << "SignalTransition::signal bindable test failed.";
         return;