QML: Take care of QVariant when converting function arguments

We cannot convert to QVariant using QMetaType::convert(). But we can
just construct a QVariant with the desired type and data. This will
become an issue once we automatically convert argument types to match
the desired type inside the function.

As a side effect, also allow declaring "var" arguments to functions.

Change-Id: Idc14021d8d85d3d09ee7b7f286de91b56ea02bfd
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qml/doc/src/cppintegration/interactqmlfromcpp.qdoc

@@ -271,9 +271,9 @@ Notice the parameter and return type specified after the colon. You can use \l
 {QML Value Types}{value types} and \l {QML Object Types}{object types} as type
 names.
 
-If the type is omitted in QML, then you must specify QVariant as type with
-Q_RETURN_ARG() and Q_ARG() when calling QMetaObject::invokeMethod.
-
+If the type is omitted or specified as \c var in QML, then you must pass
+QVariant as type with Q_RETURN_ARG() and Q_ARG() when calling
+QMetaObject::invokeMethod.
 
 \section2 Connecting to QML Signals
 

src/qml/jsruntime/qv4vme_moth.cpp

@@ -461,9 +461,17 @@ void VME::exec(MetaTypesStackFrame *frame, ExecutionEngine *engine)
 
         Q_ASSERT(argumentType.sizeOf() > 0);
         Q_ALLOCA_VAR(void, arg, argumentType.sizeOf());
+
+        if (argumentType == QMetaType::fromType<QVariant>()) {
+            if (frame->argc() > i)
+                new (arg) QVariant(frame->argTypes()[i], frame->argv()[i]);
+            else
+                new (arg) QVariant();
+        } else {
             argumentType.construct(arg);
             if (frame->argc() > i)
                 QMetaType::convert(frame->argTypes()[i], frame->argv()[i], argumentType, arg);
+        }
 
         transformedArguments[i] = arg;
     }

src/qml/parser/qqmljs.g

@@ -1680,6 +1680,9 @@ Type: UiQualifiedId;
     } break;
 ./
 
+Type: T_VAR;
+/.  case $rule_number: Q_FALLTHROUGH(); ./
+
 Type: T_VOID;
 /.
     case $rule_number: {

tests/auto/qml/qmlcppcodegen/CMakeLists.txt

@@ -4,7 +4,7 @@ qt_internal_add_test(tst_qmlcppcodegen
     SOURCES
         tst_qmlcppcodegen.cpp
     LIBRARIES
-        Qt::Qml
+        Qt::QmlPrivate
         Qt::Gui
         codegen_test_module
         codegen_test_moduleplugin

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

@@ -65,6 +65,7 @@ set(qml_files
     functionLookup.qml
     funcWithParams.qml
     functionReturningVoid.qml
+    functionTakingVar.qml
     globals.qml
     idAccess.qml
     immediateQuit.qml

tests/auto/qml/qmlcppcodegen/data/functionTakingVar.qml

@@ -0,0 +1,11 @@
+pragma Strict
+import QtQml
+
+QtObject {
+    property var c;
+
+    function a(b: var) {
+        c = b;
+    }
+
+}

tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp

@@ -23,6 +23,8 @@
 #include <data/cppbaseclass.h>
 #include <data/objectwithmethod.h>
 
+#include <QtQml/private/qqmlengine_p.h>
+
 #include <QtTest>
 #include <QtQml>
 #include <QtGui/qcolor.h>
@@ -121,6 +123,7 @@ private slots:
     void blockComments();
     void functionLookup();
     void objectInVar();
+    void functionTakingVar();
 };
 
 void tst_QmlCppCodegen::simpleBinding()
@@ -1824,6 +1827,26 @@ void tst_QmlCppCodegen::objectInVar()
     QVERIFY(!result);
 }
 
+void tst_QmlCppCodegen::functionTakingVar()
+{
+    QQmlEngine engine;
+    const QUrl document(u"qrc:/TestTypes/functionTakingVar.qml"_qs);
+    QQmlComponent c(&engine, document);
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(o);
+
+    QVERIFY(!o->property("c").isValid());
+
+    int value = 11;
+    QQmlEnginePrivate *e = QQmlEnginePrivate::get(&engine);
+    void *args[] = { nullptr, reinterpret_cast<void *>(std::addressof(value)) };
+    QMetaType types[] = { QMetaType::fromType<void>(), QMetaType::fromType<std::decay_t<int>>() };
+    e->executeRuntimeFunction(document, 0, o.data(), 1, args, types);
+
+    QCOMPARE(o->property("c"), QVariant::fromValue<int>(11));
+}
+
 void tst_QmlCppCodegen::runInterpreted()
 {
     if (qEnvironmentVariableIsSet("QV4_FORCE_INTERPRETER"))