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

For Qt Widgets we thought it was a good idea to also store in the cache
if a class didn't have a factory plugin. This worked fine there, since
the number of QWidget classnames is quite limited (so the factory plugin
cache will soon reach a limit)

In QML however, classes are often suffixed with e.g. Button_QMLTYPE_123,
Button_QMLTYPE_124 etc.
This number suffix is just increased continuously. This could lead to that
the factory plugin cache will grow ad infinitum, which will cause
"memory leaks" in addition to a performance penalty.

Pick-to: 6.0
Pick-to: 5.15
Fixes: QTBUG-75106
Change-Id: I9ba189f989f0b90ab62a2c54a2e9230236a998d8
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 4 insertions, 5 deletions

diff --git a/src/gui/accessible/qaccessible.cpp b/src/gui/accessible/qaccessible.cpp
index f2bc48fd0c..dc6794ac9c 100644
--- a/src/gui/accessible/qaccessible.cpp
+++ b/src/gui/accessible/qaccessible.cpp
@@ -695,15 +695,14 @@ 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)
-                factory = qobject_cast<QAccessiblePlugin *>(loader()->instance(index));
-            qAccessiblePlugins()->insert(cn, factory);
+            if (index != -1) {
+                QAccessiblePlugin *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);