Engine: Handle grouped property bindings of non-registered types

It is possible to expose a type to QML which exposes a QObject (derived)
property, which then gets used to create a grouped binding. The type of
the property might not have been registered in QML, or it might be part
of a base class which exposes the type already in another module. If
that module is not imported (or does not exist at all), the property
creator would so far bail out. Simply skipping the check would lead to
crashes further down, as we also lack the property cache needed during
object creation.

However, in Qt 6, we can lift this restriction: We can retrieve the
property's metatype, and from there we can fetch the metaobject. Once we
have the metaobject, we can on-demand create a property-cache for it,
and use that later in the object creator.

One restriction we add is that the type must not have a dynamic
meta-object, given that those don't lend themselves to usable propety
caches (given their dynamic nature.) The early check in the property
validator is adjusted accordingly.

Add a quick test to verify that gadgets continue to work as before.
As a drive-by, convert a few repeated QString::arg calls to a single
call of the variadic overload.

Task-number: QTBUG-122321
Pick-to: 6.7
Change-Id: I860af981250a70f541794b57db3764415ea172f0
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>

1 files changed, 15 insertions, 7 deletions

diff --git a/src/qml/qml/qqmlpropertyvalidator.cpp b/src/qml/qml/qqmlpropertyvalidator.cpp
index a49393e425..5ae3829c27 100644
--- a/src/qml/qml/qqmlpropertyvalidator.cpp
+++ b/src/qml/qml/qqmlpropertyvalidator.cpp
@@ -302,17 +302,25 @@ QVector<QQmlError> QQmlPropertyValidator::validateObject(
                         return recordError(
                                     binding->location,
                                     tr("Invalid grouped property access: Property \"%1\" with primitive type \"%2\".")
-                                        .arg(name)
-                                        .arg(QString::fromUtf8(type.name()))
+                                        .arg(name, QString::fromUtf8(type.name()))
                                     );
                     }
 
                     if (!QQmlMetaType::propertyCacheForType(type)) {
-                        return recordError(binding->location,
-                                           tr("Invalid grouped property access: Property \"%1\" with type \"%2\", which is not a value type")
-                                           .arg(name)
-                                           .arg(QString::fromUtf8(type.name()))
-                                          );
+                        auto mo = type.metaObject();
+                        if (!mo) {
+                            return recordError(binding->location,
+                                               tr("Invalid grouped property access: Property \"%1\" with type \"%2\", which is neither a value nor an object type")
+                                               .arg(name, QString::fromUtf8(type.name()))
+                                              );
+                        }
+                        if (QMetaObjectPrivate::get(mo)->flags & DynamicMetaObject) {
+                            return recordError(binding->location,
+                                               QString::fromLatin1("Unsupported grouped property access: Property \"%1\" with type \"%2\" has a dynamic meta-object.")
+                                               .arg(name, QString::fromUtf8(type.name()))
+                                               );
+                        }
+                        // fall through, this is okay
                     }
                 }
             }