QQmlComponent: Check for existence of engine

Avoid a crash when setData or create are
called after a user mistakenly used the internal constructor of
QQmlComponent which does not take an engine.

Fixes: QTBUG-55407
Change-Id: Ia4295d1b044723efce1a95607349561d4f1640da
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

2 files changed, 24 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlcomponent.cpp b/src/qml/qml/qqmlcomponent.cpp
index a23a322df9..7ad9310160 100644
--- a/src/qml/qml/qqmlcomponent.cpp
+++ b/src/qml/qml/qqmlcomponent.cpp
@@ -571,6 +571,12 @@ void QQmlComponent::setData(const QByteArray &data, const QUrl &url)
 {
     Q_D(QQmlComponent);
 
+    if (!d->engine) {
+        // ###Qt6: In Qt 6, it should be impossible for users to create a QQmlComponent without an engine, and we can remove this check
+        qWarning("QQmlComponent: Must provide an engine before calling setData");
+        return;
+    }
+
     d->clear();
 
     d->url = url;
@@ -777,6 +783,12 @@ QObject *QQmlComponent::create(QQmlContext *context)
     Q_D(QQmlComponent);
     QML_MEMORY_SCOPE_URL(url());
 
+    if (!d->engine) {
+        // ###Qt6: In Qt 6, it should be impossible for users to create a QQmlComponent without an engine, and we can remove this check
+        qWarning("QQmlComponent: Must provide an engine before calling create");
+        return nullptr;
+    }
+
     if (!context)
         context = d->engine->rootContext();
 
diff --git a/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp b/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp
index 7c7c7d3bd0..a872cece96 100644
--- a/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp
+++ b/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp
@@ -121,6 +121,7 @@ private slots:
     void setNonExistentInitialProperty();
     void relativeUrl_data();
     void relativeUrl();
+    void setDataNoEngineNoSegfault();
 
 private:
     QQmlEngine engine;
@@ -654,6 +655,17 @@ void tst_qqmlcomponent::relativeUrl()
     QVERIFY2(!component.isError(), qPrintable(component.errorString()));
 }
 
+void tst_qqmlcomponent::setDataNoEngineNoSegfault()
+{
+    QQmlEngine eng;
+    QQmlComponent comp;
+    QTest::ignoreMessage(QtWarningMsg, "QQmlComponent: Must provide an engine before calling setData");
+    comp.setData("import QtQuick 1.0; QtObject { }", QUrl(""));
+    QTest::ignoreMessage(QtWarningMsg, "QQmlComponent: Must provide an engine before calling create");
+    auto c = comp.create();
+    QVERIFY(!c);
+}
+
 QTEST_MAIN(tst_qqmlcomponent)
 
 #include "tst_qqmlcomponent.moc"