qqmlapplicationengine: Handle errors during component creation

Previously QQmlApplicationEngine did not handle any errors that occurred during object creation
(i.e. failures to initialize required properties) which lead to QObject::connect errors and to
the error messages not getting printed among other issues.

Change-Id: I69bc566a6d349c786cae82a963a621388684c8f5
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 890cb4cb236333fd5b112fffc0e9088ecb43f2df)

4 files changed, 35 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlapplicationengine.cpp b/src/qml/qml/qqmlapplicationengine.cpp
index 9af3437cb0..8f7f2e48eb 100644
--- a/src/qml/qml/qqmlapplicationengine.cpp
+++ b/src/qml/qml/qqmlapplicationengine.cpp
@@ -146,6 +146,14 @@ void QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *c)
         break;
     case QQmlComponent::Ready: {
         auto newObj = initialProperties.empty() ? c->create() : c->createWithInitialProperties(initialProperties);
+
+        if (c->isError()) {
+           qWarning() << "QQmlApplicationEngine failed to create component";
+           warning(c->errors());
+           q->objectCreated(nullptr, c->url());
+           break;
+        }
+
         objects << newObj;
         QObject::connect(newObj, &QObject::destroyed, q, [&](QObject *obj) { objects.removeAll(obj); });
         q->objectCreated(objects.constLast(), c->url());
diff --git a/tests/auto/qml/qqmlapplicationengine/data/Required.qml b/tests/auto/qml/qqmlapplicationengine/data/Required.qml
new file mode 100644
index 0000000000..acf4a00ce6
--- /dev/null
+++ b/tests/auto/qml/qqmlapplicationengine/data/Required.qml
@@ -0,0 +1,6 @@
+import QtQml 2.15
+
+QtObject
+{
+    required property int foo
+}
diff --git a/tests/auto/qml/qqmlapplicationengine/data/requiredViolation.qml b/tests/auto/qml/qqmlapplicationengine/data/requiredViolation.qml
new file mode 100644
index 0000000000..c5de4661a9
--- /dev/null
+++ b/tests/auto/qml/qqmlapplicationengine/data/requiredViolation.qml
@@ -0,0 +1,3 @@
+import QtQml 2.15
+
+Required {}
diff --git a/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp b/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp
index f636e527c3..4306c7b8ca 100644
--- a/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp
+++ b/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp
@@ -56,6 +56,7 @@ private slots:
     void translationChange();
     void setInitialProperties();
     void failureToLoadTriggersWarningSignal();
+    void errorWhileCreating();
 
 private:
     QString buildDir;
@@ -333,6 +334,23 @@ void tst_qqmlapplicationengine::failureToLoadTriggersWarningSignal()
     QTRY_COMPARE(warningObserver.count(), 1);
 }
 
+void tst_qqmlapplicationengine::errorWhileCreating()
+{
+    auto url = testFileUrl("requiredViolation.qml");
+    QQmlApplicationEngine test;
+    QSignalSpy observer(&test, &QQmlApplicationEngine::objectCreated);
+
+    QTest::ignoreMessage(QtMsgType::QtWarningMsg, "QQmlApplicationEngine failed to create component");
+    QTest::ignoreMessage(QtMsgType::QtWarningMsg, qPrintable(QStringLiteral("%1:5:5: Required property foo was not initialized").arg(testFileUrl("Required.qml").toString())));
+
+    test.load(url);
+
+    QTRY_COMPARE(observer.count(), 1);
+    QList<QVariant> args = observer.takeFirst();
+    QVERIFY(args.at(0).isNull());
+    QCOMPARE(args.at(1).toUrl(), url);
+}
+
 QTEST_MAIN(tst_qqmlapplicationengine)
 
 #include "tst_qqmlapplicationengine.moc"