QML: Remove static attchedPropertyIds map

If the same object is available under two different names it should
still have the same attached properties no matter which name you use.

This was achieved by having a static map of metaobjects to attached
property IDs that would always hold the first attached property ID
registered for a given metaobject. This attached property ID was then
used as key in the map of attached properties for the actual objects.

The obvious downside to that is that we need a global static which gives
us thread safety and static initialization (and destruction) problems.

It turns out, all the attached properties are created by attached
properties functions, registered by the user. Those functions only get
the object to be amended as parameter. Therefore, no attached properties
function can be registered for multiple attached properties on the same
object as it wouldn't know which one to create for a given call. Thus,
the whole ID dance is unnecessary as we can as well index the attached
property objects by the function that created them. This nicely avoids
creating two attached property objects for the same object and function
and still makes the global static unnecessary.

Fixes: QTBUG-75176
Change-Id: Ie8d53ef0a6f41c9b3d6b9d611cde1603a557901c
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/qml/qml/qqml.h b/src/qml/qml/qqml.h
index 05a9f70247..9eacc5bc22 100644
--- a/src/qml/qml/qqml.h
+++ b/src/qml/qml/qqml.h
@@ -582,6 +582,10 @@ namespace QtQml {
     Q_QML_EXPORT QObject *qmlAttachedPropertiesObjectById(int, const QObject *, bool create = true);
     Q_QML_EXPORT QObject *qmlAttachedPropertiesObject(int *, const QObject *,
                                                       const QMetaObject *, bool create);
+    Q_QML_EXPORT QQmlAttachedPropertiesFunc qmlAttachedPropertiesFunction(QObject *,
+                                                                          const QMetaObject *);
+    Q_QML_EXPORT QObject *qmlAttachedPropertiesObject(QObject *, QQmlAttachedPropertiesFunc func,
+                                                      bool create = true);
 #ifndef Q_QDOC
 }
 #endif
@@ -601,8 +605,9 @@ Q_QML_EXPORT void qmlRegisterModule(const char *uri, int versionMajor, int versi
 template<typename T>
 QObject *qmlAttachedPropertiesObject(const QObject *obj, bool create = true)
 {
-    static int idx = -1;
-    return qmlAttachedPropertiesObject(&idx, obj, &T::staticMetaObject, create);
+    QObject *mutableObj = const_cast<QObject *>(obj);
+    return qmlAttachedPropertiesObject(
+            mutableObj, qmlAttachedPropertiesFunction(mutableObj, &T::staticMetaObject), create);
 }
 
 Q_QML_EXPORT void qmlRegisterBaseTypes(const char *uri, int versionMajor, int versionMinor);