QJSValue: convert more aggressively to QVariant

Normally, we don't want to convert aggressively between JS objects and
QVariant, as that is prone to losing information. However,
QJSValue::toVariant is documented to attempt lossy conversions. Restore
the behavior of Qt < 6.5.3 for it. This is done by replacing the boolean
indicating we should wrap JS objects into QJSValue with an enum instead.
That enum introduces a third state ("Aggressive"), which is only used
for QJSValue::toVariant. All other users of QJSEngine::toVariant behave
as before (post 6.5.3).
Function objects are still not converted, as we know that this would be
a futile attempt, and more importantly, to keep the behavior that
existed  before Qt 6.5.3.
Amends 43077556550c6b17226a7d393ec844b605c9c678 which introduced the
regression and afe96c4d633146df477012975824b8ab65034239 which  fixed the
issue only partially.

Pick-to: 6.5 6.6 6.7
Fixes: QTBUG-119963
Change-Id: I07d9901437812579ac5b873a4dff4de60c8f617e
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/qml/jsapi/qjsvalue.cpp b/src/qml/jsapi/qjsvalue.cpp
index bc75526e8d..f622c3fb23 100644
--- a/src/qml/jsapi/qjsvalue.cpp
+++ b/src/qml/jsapi/qjsvalue.cpp
@@ -638,8 +638,11 @@ QVariant QJSValue::toVariant(QJSValue::ObjectConversionBehavior behavior) const
     if (val.isString())
         return QVariant(val.toQString());
     if (val.as<QV4::Managed>()) {
-        return QV4::ExecutionEngine::toVariant(
-                    val, /*typeHint*/ QMetaType{}, behavior == RetainJSObjects);
+        if (behavior == RetainJSObjects)
+            return QV4::ExecutionEngine::toVariant(
+                    val, /*typeHint*/ QMetaType{}, /*createJSValueForObjectsAndSymbols=*/ true);
+        else
+            return QV4::ExecutionEngine::toVariantLossy(val);
     }
 
     Q_ASSERT(false);