QQmlInfo: print ancestor of object if it has no QML engine

This results in the following message for objects without a QML engine:

QML AttachedObject (parent or ancestor of Attached): Binding loop
detected for property "a"

for this QML file, named AttachedObject.qml:

import QtQuick 2.0
import org.qtproject.Test 1.0

Item {
    Attached.a: Attached.a
}

This, in turn, allows the warning to be emitted via the
QQmlEngine::warnings signal, since QQmlEnginePrivate::warning() is now
passed a valid engine. This solves the awkward situation where a
binding loop warning can not be detected at all by auto tests involving
attached C++ objects (as message handlers do not receive these messages
either).

Pick-to: 5.15
Change-Id: I07589974207bd5448d22a6086a52b9230d23e298
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 32 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmlinfo/tst_qqmlinfo.cpp b/tests/auto/qml/qqmlinfo/tst_qqmlinfo.cpp
index 706102e6fe..bb96ba319c 100644
--- a/tests/auto/qml/qqmlinfo/tst_qqmlinfo.cpp
+++ b/tests/auto/qml/qqmlinfo/tst_qqmlinfo.cpp
@@ -27,6 +27,7 @@
 ****************************************************************************/
 
 #include <qtest.h>
+#include <QtTest/qsignalspy.h>
 #include <QQmlEngine>
 #include <QQmlComponent>
 #include <QTimer>
@@ -34,6 +35,8 @@
 #include <qqmlinfo.h>
 #include "../../shared/util.h"
 
+#include "attached.h"
+
 class tst_qqmlinfo : public QQmlDataTest
 {
     Q_OBJECT
@@ -51,6 +54,7 @@ private slots:
     void chaining();
     void messageTypes();
     void component();
+    void attachedObject();
 
 private:
     QQmlEngine engine;
@@ -230,6 +234,34 @@ void tst_qqmlinfo::component()
     qmlInfo(delegate) << "Delegate error";
 }
 
+void tst_qqmlinfo::attachedObject()
+{
+    QQmlComponent component(&engine, testFileUrl("AttachedObject.qml"));
+
+    QSignalSpy warningSpy(&engine, SIGNAL(warnings(const QList<QQmlError> &)));
+    QVERIFY(warningSpy.isValid());
+
+    const QString qmlBindingLoopMessage = "QML Rectangle: Binding loop detected for property \"width\"";
+    const QString qmlBindingLoopMessageFull = component.url().toString() + ":7:5: " + qmlBindingLoopMessage;
+    QTest::ignoreMessage(QtWarningMsg, qPrintable(qmlBindingLoopMessageFull));
+
+    const QString cppBindingLoopMessage = "QML AttachedObject (parent or ancestor of Attached): Binding loop detected for property \"a\"";
+    const QString cppBindingLoopMessageFull = component.url().toString() + ":4:1: " + cppBindingLoopMessage;
+    QTest::ignoreMessage(QtWarningMsg, qPrintable(cppBindingLoopMessageFull));
+
+    QScopedPointer<QObject> object(component.create());
+    QVERIFY2(object != nullptr, qPrintable(component.errorString()));
+    QCOMPARE(warningSpy.count(), 2);
+
+    // The Attached C++ type has no QML engine since it was created in C++, so we should see its parent instead.
+    const auto cppWarnings = warningSpy.at(0).first().value<QList<QQmlError>>();
+    QCOMPARE(cppWarnings.first().description(), cppBindingLoopMessage);
+
+    // The QML type has a QML engine, so we should see the normal message.
+    const auto qmlWarnings = warningSpy.at(1).first().value<QList<QQmlError>>();
+    QCOMPARE(qmlWarnings.first().description(), qmlBindingLoopMessage);
+}
+
 QTEST_MAIN(tst_qqmlinfo)
 
 #include "tst_qqmlinfo.moc"