Don't crash when a signal/slot connection outlives the engine

In the test case in the bug, the signal was emitted from the QApplication
destructor (somewhere from the qpa plugin when the platform windows were
destroyed)

Task-number: QTBUG-37351
Change-Id: Ieec59e12be10bab1428743b80eecdf22ef9d8bf6
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/qml/jsruntime/qv4qobjectwrapper.cpp b/src/qml/jsruntime/qv4qobjectwrapper.cpp
index 004c3eb036..1cfd2d88ec 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper.cpp
+++ b/src/qml/jsruntime/qv4qobjectwrapper.cpp
@@ -751,13 +751,18 @@ struct QObjectSlotDispatcher : public QtPrivate::QSlotObjectBase
         break;
         case Call: {
             QObjectSlotDispatcher *This = static_cast<QObjectSlotDispatcher*>(this_);
+            QV4::ExecutionEngine *v4 = This->function.engine();
+            // Might be that we're still connected to a signal that's emitted long
+            // after the engine died. We don't track connections in a global list, so
+            // we need this safeguard.
+            if (!v4)
+                break;
+
             QVarLengthArray<int, 9> dummy;
             int *argsTypes = QQmlPropertyCache::methodParameterTypes(r, This->signalIndex, dummy, 0);
 
             int argCount = argsTypes ? argsTypes[0]:0;
 
-            QV4::ExecutionEngine *v4 = This->function.engine();
-            Q_ASSERT(v4);
             QV4::Scope scope(v4);
             QV4::ScopedFunctionObject f(scope, This->function.value());
             QV4::ExecutionContext *ctx = v4->currentContext();