QDesktopServices: deprecate destroying URL handlers w/o explicit unsetUrlHandler()

[ChangeLog][QtGui][QDesktopServices] URL handlers that have been passed
to setUrlHandler() must now be removed by calling unsetUrlHandler()
before they are destroyed. Relying on the handler's destructor to
implicitly unset it is now deprecated, because it may already be in use
by concurrent openUrl() calls. Support for implicit unsetting will be
removed in 6.6 and, until then, a qWarning() is raised if it is
exercised.

Fixes: QTBUG-100775
Fixes: QTBUG-100779
Pick-to: 6.3 6.2 5.15
Change-Id: I0c4f91b78f847b135fdeb38766babc892bdc1379
Reviewed-by: Qt CI Bot <[email protected]>
Reviewed-by: Sona Kurazyan <[email protected]>

2 files changed, 37 insertions, 0 deletions

diff --git a/src/gui/util/qdesktopservices.cpp b/src/gui/util/qdesktopservices.cpp
index fd3761a4734..8f237960d65 100644
--- a/src/gui/util/qdesktopservices.cpp
+++ b/src/gui/util/qdesktopservices.cpp
@@ -74,13 +74,16 @@ public:
     typedef QHash<QString, Handler> HandlerHash;
     HandlerHash handlers;
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
 public Q_SLOTS:
     void handlerDestroyed(QObject *handler);
+#endif
 
 };
 
 Q_GLOBAL_STATIC(QOpenUrlHandlerRegistry, handlerRegistry)
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
 void QOpenUrlHandlerRegistry::handlerDestroyed(QObject *handler)
 {
     const auto lock = qt_scoped_lock(mutex);
@@ -88,11 +91,16 @@ void QOpenUrlHandlerRegistry::handlerDestroyed(QObject *handler)
     while (it != handlers.end()) {
         if (it->receiver == handler) {
             it = handlers.erase(it);
+            qWarning("Please call QDesktopServices::unsetUrlHandler() before destroying a "
+                     "registered URL handler object.\n"
+                     "Support for destroying a registered URL handler object is deprecated, "
+                     "and will be removed in Qt 6.6.");
         } else {
             ++it;
         }
     }
 }
+#endif
 
 /*!
     \class QDesktopServices
@@ -255,6 +263,10 @@ bool QDesktopServices::openUrl(const QUrl &url)
     Note that the handler will always be called from within the same thread that
     calls QDesktopServices::openUrl().
 
+    You must call unsetUrlHandler() before destroying the handler object, so
+    the destruction of the handler object does not overlap with concurrent
+    invocations of openUrl() using it.
+
     \section1 iOS
 
     To use this function for receiving data from other apps on iOS you also need to
@@ -323,14 +335,20 @@ void QDesktopServices::setUrlHandler(const QString &scheme, QObject *receiver, c
     h.receiver = receiver;
     h.name = method;
     registry->handlers.insert(scheme.toLower(), h);
+#if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
     QObject::connect(receiver, SIGNAL(destroyed(QObject*)),
                      registry, SLOT(handlerDestroyed(QObject*)),
                      Qt::DirectConnection);
+#endif
 }
 
 /*!
     Removes a previously set URL handler for the specified \a scheme.
 
+    Call this function before the handler object that was registered for \a scheme
+    is destroyed, to prevent concurrent openUrl() calls from continuing to call
+    the destroyed handler object.
+
     \sa setUrlHandler()
 */
 void QDesktopServices::unsetUrlHandler(const QString &scheme)
diff --git a/tests/auto/gui/util/qdesktopservices/tst_qdesktopservices.cpp b/tests/auto/gui/util/qdesktopservices/tst_qdesktopservices.cpp
index 7446f8ed9fa..4df34280b04 100644
--- a/tests/auto/gui/util/qdesktopservices/tst_qdesktopservices.cpp
+++ b/tests/auto/gui/util/qdesktopservices/tst_qdesktopservices.cpp
@@ -65,6 +65,10 @@ public slots:
     }
 };
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 6, 0)
+# define CAN_IMPLICITLY_UNSET
+#endif
+
 void tst_qdesktopservices::handlers()
 {
     MyUrlHandler fooHandler;
@@ -72,6 +76,12 @@ void tst_qdesktopservices::handlers()
 
     QDesktopServices::setUrlHandler(QString("foo"), &fooHandler, "handle");
     QDesktopServices::setUrlHandler(QString("bar"), &barHandler, "handle");
+#ifndef CAN_IMPLICITLY_UNSET
+    const auto unsetHandlers = qScopeGuard([] {
+        QDesktopServices::unsetUrlHandler(u"bar"_qs);
+        QDesktopServices::unsetUrlHandler(u"foo"_qs);
+    });
+#endif
 
     QUrl fooUrl("foo://blub/meh");
     QUrl barUrl("bar://hmm/hmmmm");
@@ -81,6 +91,15 @@ void tst_qdesktopservices::handlers()
 
     QCOMPARE(fooHandler.lastHandledUrl.toString(), fooUrl.toString());
     QCOMPARE(barHandler.lastHandledUrl.toString(), barUrl.toString());
+
+#ifdef CAN_IMPLICITLY_UNSET
+    for (int i = 0; i < 2; ++i)
+        QTest::ignoreMessage(QtWarningMsg,
+                             "Please call QDesktopServices::unsetUrlHandler() before destroying a "
+                             "registered URL handler object.\n"
+                             "Support for destroying a registered URL handler object is deprecated, "
+                             "and will be removed in Qt 6.6.");
+#endif
 }
 
 QTEST_MAIN(tst_qdesktopservices)