QmlCompiler: Reject conversions via QJSValue

Those are generally less efficient than what the interpreter would do,
they can have side effects, and they can throw exceptions. We don't want
to deal with any of that. Most of those implicit conversions have
explicit equivalents. For those that don't we can add them.

Pick-to: 6.2 6.4
Fixes: QTBUG-104010
Change-Id: I62898db92219386c94f2a6c9b56f6fb0b7578832
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>

src/qmlcompiler/qqmljscodegenerator.cpp

@@ -2060,8 +2060,8 @@ void QQmlJSCodeGenerator::generate_Mod(int lhs)
     const auto rhsVar = conversion(
                 m_state.accumulatorIn().storedType(), m_typeResolver->jsPrimitiveType(),
                 m_state.accumulatorVariableIn);
-    Q_ASSERT(!lhsVar.isEmpty());
-    Q_ASSERT(!rhsVar.isEmpty());
+    Q_ASSERT(m_error->isValid() || !lhsVar.isEmpty());
+    Q_ASSERT(m_error->isValid() || !rhsVar.isEmpty());
 
     m_body += m_state.accumulatorVariableOut;
     m_body += u" = "_s;
@@ -2262,8 +2262,8 @@ void QQmlJSCodeGenerator::generateArithmeticOperation(int lhs, const QString &cp
                                    registerVariable(lhs));
     const auto rhsVar = conversion(m_state.accumulatorIn(), m_state.readAccumulator(),
                                    m_state.accumulatorVariableIn);
-    Q_ASSERT(!lhsVar.isEmpty());
-    Q_ASSERT(!rhsVar.isEmpty());
+    Q_ASSERT(m_error->isValid() || !lhsVar.isEmpty());
+    Q_ASSERT(m_error->isValid() || !rhsVar.isEmpty());
 
     const QQmlJSRegisterContent originalOut = m_typeResolver->original(m_state.accumulatorOut());
     m_body += m_state.accumulatorVariableOut;
@@ -2611,10 +2611,10 @@ QString QQmlJSCodeGenerator::conversion(const QQmlJSScope::ConstPtr &from,
             return u"QJSPrimitiveValue("_s + variable + u')' + retrieve;
     }
 
-    // TODO: more efficient string conversions, possibly others
+    // TODO: add more conversions
 
-    return u"aotContext->engine->fromScriptValue<"_s + castTargetName(to)
-            + u">(aotContext->engine->toScriptValue("_s + variable + u"))"_s;
+    reject(u"conversion from "_s + from->internalName() + u" to "_s + to->internalName());
+    return QString();
 }
 
 int QQmlJSCodeGenerator::nextJSLine(uint line) const

tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt

@@ -133,6 +133,7 @@ set(qml_files
     text.qml
     themerbad.qml
     themergood.qml
+    toString.qml
     typePropertyClash.qml
     typedArray.qml
     undefinedResets.qml

tests/auto/qml/qmlcppcodegen/data/failures.qml

@@ -3,6 +3,7 @@ import TestTypes
 import Ambiguous 1.2
 
 QtObject {
+    id: self
     property string attachedForNonObject: objectName.Component.objectName
     property string attachedForNasty: Nasty.objectName
 
@@ -27,4 +28,6 @@ QtObject {
     }
 
     Component.onCompleted: doesNotExist()
+
+    property string aString: self + "a"
 }

tests/auto/qml/qmlcppcodegen/data/toString.qml

@@ -0,0 +1,13 @@
+import QtQml
+
+QtObject {
+    id: self
+    property QtObject other: QtObject {
+        function toString() : string { throw "no" }
+    }
+
+    function toString() : string { return "yes" }
+
+    property string yes: self + " yes"
+    property string no: other + " no"
+}

tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp

@@ -120,6 +120,7 @@ private slots:
     void boundComponents();
     void invisibleListElementType();
     void typePropertyClash();
+    void objectToString();
 };
 
 void tst_QmlCppCodegen::simpleBinding()
@@ -2194,6 +2195,20 @@ void tst_QmlCppCodegen::typePropertyClash()
     QCOMPARE(o->objectName(), u"Size: 5"_s);
 }
 
+void tst_QmlCppCodegen::objectToString()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, QUrl(u"qrc:/TestTypes/toString.qml"_s));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+
+    QTest::ignoreMessage(QtWarningMsg, "qrc:/TestTypes/toString.qml:6: no");
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+
+    QCOMPARE(o->property("yes").toString(), u"yes yes"_s);
+    QCOMPARE(o->property("no").toString(), u" no"_s); // throws, but that is ignored
+}
+
 void tst_QmlCppCodegen::runInterpreted()
 {
 #ifdef Q_OS_ANDROID