QQmlJSCodeGenerator: fix nullptr dereference

If we try to lookup the length of a generic QVariant, we fail, and so
far crashed. We should ideally detect that we are dealing with an array
(and thus length is a known, available property), but for now simply
reject compilation to C++.

Pick-to: 6.4
Fixes: QTBUG-109164
Change-Id: I9d4149ac09a351754d012dbc829774413d6b32eb
Reviewed-by: Semih Yavuz <semih.yavuz@qt.io>
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>

5 files changed, 84 insertions, 0 deletions

diff --git a/tests/auto/qml/qmlcppcodegen/data/ArraySequenceLengthInterop.qml b/tests/auto/qml/qmlcppcodegen/data/ArraySequenceLengthInterop.qml
new file mode 100644
index 0000000000..51c9f5fdb1
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/ArraySequenceLengthInterop.qml
@@ -0,0 +1,24 @@
+import QtQml
+import TestTypes
+
+QtObject {
+    property var seq:  SequenceTypeExample {
+        id: mySequence
+    }
+
+    property int length: mySequence.qrealListProperty.length
+
+    function goodSequenceWrite() {
+        var someData = [1.1, 2.2, 3.3]
+        someData.length = 100;
+        for (var i = 0; i < 5; ++i) {
+            for (var j = 0; j < 100; ++j) {
+                someData[j] = j;
+            }
+            //Modifies entire sequence at once by copying a temp variable
+            mySequence.qrealListProperty = someData;
+        }
+    }
+
+    Component.onCompleted: goodSequenceWrite()
+}
diff --git a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
index 182c9baac5..2cdbdfbb58 100644
--- a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
+++ b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
@@ -13,6 +13,7 @@ set(cpp_sources
     multiforeign.h
     objectwithmethod.h
     person.cpp person.h
+    sequencetypeexample.cpp sequencetypeexample.h
     state.h
     theme.cpp theme.h
     timelinetheme.cpp timelinetheme.h
@@ -21,6 +22,7 @@ set(cpp_sources
 
 set(qml_files
     AccessModelMethodsFromOutside.qml
+    ArraySequenceLengthInterop.qml
     BadType.qml
     BaseMember.qml
     BindingExpression.qml
diff --git a/tests/auto/qml/qmlcppcodegen/data/sequencetypeexample.cpp b/tests/auto/qml/qmlcppcodegen/data/sequencetypeexample.cpp
new file mode 100644
index 0000000000..dc74ed9e28
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/sequencetypeexample.cpp
@@ -0,0 +1,18 @@
+#include "sequencetypeexample.h"
+
+SequenceTypeExample::SequenceTypeExample()
+    : QObject()
+{
+    m_list << 1.1 << 2.2 << 3.3;
+}
+
+QList<qreal> SequenceTypeExample::qrealListProperty() const
+{
+    return m_list;
+}
+
+void SequenceTypeExample::setQrealListProperty(const QList<qreal> &list)
+{
+    m_list = list;
+    emit qrealListPropertyChanged();
+}
diff --git a/tests/auto/qml/qmlcppcodegen/data/sequencetypeexample.h b/tests/auto/qml/qmlcppcodegen/data/sequencetypeexample.h
new file mode 100644
index 0000000000..e15306667d
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/sequencetypeexample.h
@@ -0,0 +1,29 @@
+#ifndef SEQENCETYPEEXAMPLE_H
+#define SEQENCETYPEEXAMPLE_H
+
+#include <QDebug>
+#include <QObject>
+#include <QtQml>
+
+class SequenceTypeExample : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+    Q_PROPERTY (QList<qreal> qrealListProperty READ qrealListProperty WRITE setQrealListProperty
+                NOTIFY qrealListPropertyChanged)
+
+public:
+    explicit SequenceTypeExample();
+
+    QList<qreal> qrealListProperty() const;
+    void setQrealListProperty(const QList<qreal> &list);
+
+signals:
+    void qrealListPropertyChanged();
+
+private :
+    QList<qreal> m_list;
+
+};
+
+#endif // SEQENCETYPEEXAMPLE_H
diff --git a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
index 2cbf2bc747..a275fff918 100644
--- a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
+++ b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
@@ -154,6 +154,7 @@ private slots:
     void enumConversion();
     void ambiguousSignals();
     void fileImportsContainCxxTypes();
+    void lengthAccessArraySequenceCompat();
 };
 
 void tst_QmlCppCodegen::initTestCase()
@@ -2944,6 +2945,16 @@ void tst_QmlCppCodegen::fileImportsContainCxxTypes()
     QCOMPARE(o->objectName(), u"horst guenther"_s);
 }
 
+void tst_QmlCppCodegen::lengthAccessArraySequenceCompat()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, QUrl(u"qrc:/qt/qml/TestTypes/ArraySequenceLengthInterop.qml"_s));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+    QCOMPARE(o->property("length").toInt(), 100);
+}
+
 QTEST_MAIN(tst_QmlCppCodegen)
 
 #include "tst_qmlcppcodegen.moc"