Don't crash if queued signal handler no longer exists

Cherry-picked from qt5/script commit
c89315da2e836fe67c4228cfb73c25a68b0a3a95

Task-number: QTBUG-26261
Change-Id: I24544e2f8c36eaf19c65d9a30affd1f3e05b52bb
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

2 files changed, 40 insertions, 1 deletions

diff --git a/src/script/bridge/qscriptqobject.cpp b/src/script/bridge/qscriptqobject.cpp
index fe89f3d..e8c017d 100644
--- a/src/script/bridge/qscriptqobject.cpp
+++ b/src/script/bridge/qscriptqobject.cpp
@@ -2089,7 +2089,13 @@ void QObjectConnectionManager::execute(int slotIndex, void **argv)
             }
         }
     }
-    Q_ASSERT(slot && slot.isObject());
+    if (!slot) {
+        // This connection no longer exists (can happen if the signal is
+        // emitted from another thread and the call gets queued, but the
+        // connection is removed before the QMetaCallEvent gets processed).
+        return;
+    }
+    Q_ASSERT(slot.isObject());
 
     if (engine->isCollecting()) {
         qWarning("QtScript: can't execute signal handler during GC");
diff --git a/tests/auto/qscriptextqobject/tst_qscriptextqobject.cpp b/tests/auto/qscriptextqobject/tst_qscriptextqobject.cpp
index cb27878..11468f3 100644
--- a/tests/auto/qscriptextqobject/tst_qscriptextqobject.cpp
+++ b/tests/auto/qscriptextqobject/tst_qscriptextqobject.cpp
@@ -585,6 +585,7 @@ private slots:
     void nestedObjectAsSlotArgument_data();
     void nestedObjectAsSlotArgument();
     void propertyAccessThroughActivationObject();
+    void connectionRemovedAfterQueuedCall();
 
 private:
     QScriptEngine *m_engine;
@@ -3643,5 +3644,37 @@ void tst_QScriptExtQObject::propertyAccessThroughActivationObject()
     m_engine->popContext();
 }
 
+class SignalEmitterThread : public QThread
+{
+public:
+    SignalEmitterThread(MyQObject *sender)
+        : m_sender(sender)
+    { }
+
+    void run()
+    { m_sender->emitMySignal(); }
+
+private:
+    MyQObject *m_sender;
+};
+
+// QTBUG-26261
+void tst_QScriptExtQObject::connectionRemovedAfterQueuedCall()
+{
+    QVERIFY(m_engine->evaluate("var pass = true; function onMySignal() { pass = false; }").isUndefined());
+    QVERIFY(m_engine->evaluate("myObject.mySignal.connect(onMySignal)").isUndefined());
+
+    SignalEmitterThread thread(m_myObject);
+    QVERIFY(m_myObject->thread() != &thread); // Premise for queued call
+    thread.start();
+    QVERIFY(thread.wait());
+
+    QVERIFY(m_engine->evaluate("myObject.mySignal.disconnect(onMySignal)").isUndefined());
+    // Should not crash
+    QCoreApplication::processEvents();
+
+    QVERIFY(m_engine->evaluate("pass").toBool());
+}
+
 QTEST_MAIN(tst_QScriptExtQObject)
 #include "tst_qscriptextqobject.moc"