Revert "a11y: Do not cache classes that don't have a factory plugin"

This reverts commit 583668005d4d6399fc16d165dcb6a5af2b94323d, and
provides an alternative fix for QTBUG-75106.

Reason: This introduced QTBUG-103009, due to lack of caching. To fix the
original issue, we still reduce the amount of caching we do, by only
considering the first non-dynamic meta-object for QML related objects.

Task-number: QTBUG-75106
Fixes: QTBUG-103009
Pick-to: 6.3 6.2 5.15
Change-Id: Ic76af26a719d1114208be9555286239c6c6df615
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 25 insertions, 4 deletions

diff --git a/src/gui/accessible/qaccessible.cpp b/src/gui/accessible/qaccessible.cpp
index 30e5a32b1d..ee409bd179 100644
--- a/src/gui/accessible/qaccessible.cpp
+++ b/src/gui/accessible/qaccessible.cpp
@@ -54,6 +54,7 @@
 #include <QtCore/qdebug.h>
 #include <QtCore/qloggingcategory.h>
 #include <QtCore/qmetaobject.h>
+#include <QtCore/private/qmetaobject_p.h>
 #include <QtCore/qhash.h>
 #include <private/qfactoryloader_p.h>
 
@@ -682,6 +683,25 @@ QAccessibleInterface *QAccessible::queryAccessibleInterface(QObject *object)
     // Create a QAccessibleInterface for the object class. Start by the most
     // derived class and walk up the class hierarchy.
     const QMetaObject *mo = object->metaObject();
+    const auto *objectPriv = QObjectPrivate::get(object);
+    /*
+     We do not want to cache each and every QML metaobject (Button_QMLTYPE_124,
+     Button_QMLTYPE_125, etc.). Those dynamic metaobjects shouldn't have an
+     accessible interface in any case. Instead, we start the whole checking
+     with the first non-dynamic meta-object. To avoid potential regressions
+     in other areas of Qt that also use dynamic metaobjects, we only do this
+     for objects that are QML-related (approximated by checking whether they
+     have ddata set).
+    */
+    const bool qmlRelated = !objectPriv->isDeletingChildren &&
+                            objectPriv->declarativeData;
+    while (qmlRelated && mo) {
+        auto mop = QMetaObjectPrivate::get(mo);
+        if (!mop || !(mop->flags & DynamicMetaObject))
+            break;
+
+        mo = mo->superClass();
+    };
     while (mo) {
         const QString cn = QLatin1StringView(mo->className());
 
@@ -697,14 +717,15 @@ QAccessibleInterface *QAccessible::queryAccessibleInterface(QObject *object)
         // Find a QAccessiblePlugin (factory) for the class name. If there's
         // no entry in the cache try to create it using the plugin loader.
         if (!qAccessiblePlugins()->contains(cn)) {
+            QAccessiblePlugin *factory = nullptr; // 0 means "no plugin found". This is cached as well.
             const int index = loader()->indexOf(cn);
-            if (index != -1) {
-                QAccessiblePlugin *factory = qobject_cast<QAccessiblePlugin *>(loader()->instance(index));
-                qAccessiblePlugins()->insert(cn, factory);
-            }
+            if (index != -1)
+                factory = qobject_cast<QAccessiblePlugin *>(loader()->instance(index));
+            qAccessiblePlugins()->insert(cn, factory);
         }
 
         // At this point the cache should contain a valid factory pointer or 0:
+        Q_ASSERT(qAccessiblePlugins()->contains(cn));
         QAccessiblePlugin *factory = qAccessiblePlugins()->value(cn);
         if (factory) {
             QAccessibleInterface *result = factory->create(cn, object);