a11y: Prevent one case of losing a11y interface when setting event child

9a369a25ddfac9352cabde65c8476c7433dc6c3a added a
QAccessibleEvent ctor that takes a QAccessibleInterface*
instead of a QObject*.

Retrieving the QAccessibleInterface* later is done using the
interface's unique ID stored in the m_uniqueId member.

However, the fact that m_uniqueId is a member
of the union alongside with m_child means that setting
a child via QAccessibleEvent::setChild also overwrites
the stored unique ID, which breaks retrieving the accessible
interface later.

Fix this for the case where the QAccessibleInterface has
an associated QObject by assigning m_object in the ctor as well.
This means that a QAccessibleEvent created using either of the two
constructors (the one taking the QObject* and the one taking
the QAccessibleInterface* associated with the object) now behaves
the same.

Fixing the case where there is no associated QObject would require
further changes (e.g. adding a member for the QAccessibleInterface*
or making the m_uniqueId member a separate member instead of having
it in a union with m_child). However, I see no way to do so without
breaking the ABI, so that is left unchanged.

This also adds a corresponding test case.

Fixes: QTBUG-105988
Pick-to: 6.4
Change-Id: I71a548af0277a5034e9e207f066fa3e25c5393f3
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/accessible/qaccessible.h b/src/gui/accessible/qaccessible.h
index 2700b5c080..b5e155c01e 100644
--- a/src/gui/accessible/qaccessible.h
+++ b/src/gui/accessible/qaccessible.h
@@ -287,7 +287,7 @@ public:
     }
 
     inline QAccessibleEvent(QAccessibleInterface *iface, QAccessible::Event typ)
-        : m_type(typ), m_object(nullptr)
+        : m_type(typ)
     {
         Q_ASSERT(iface);
         Q_ASSERT(m_type != QAccessible::ValueChanged);
@@ -299,6 +299,7 @@ public:
         Q_ASSERT(m_type != QAccessible::TextUpdated);
         Q_ASSERT(m_type != QAccessible::TableModelChanged);
         m_uniqueId = QAccessible::uniqueId(iface);
+        m_object = iface->object();
     }
 
     virtual ~QAccessibleEvent();