The TypeScript control.onEvent() flags argument is not passed to the DAL/CODAL event listener

[microbit-carlos]

The control.onEvent() C++ function checks if any flag is provided, and if not it set the EventFlags::QueueIfBusy by default:

pxt-microbit/libs/core/control.cpp

Lines 304 to 307 in 5b0d30f

	void onEvent(int src, int value, Action handler, int flags = 0) {
	if (!flags) flags = ::EventFlags::QueueIfBusy;
	registerWithDal(src, value, handler, (int)flags);
	}

However, the registerWithDal() function then ignores the flags argument:

pxt-microbit/libs/core/codal.cpp

Lines 99 to 104 in 5b0d30f

	void registerWithDal(int id, int event, Action a, int flags) {
	uBit.messageBus.ignore(id, event, dispatchForeground);
	uBit.messageBus.listen(id, event, dispatchForeground, a);
	incr(a);
	registerGCPtr(a);
	}

So, it ultimately depends on the CODAL default beings set to MESSAGE_BUS_LISTENER_QUEUE_IF_BUSY via the EVENT_LISTENER_DEFAULT_FLAGS config:

• codal-core/inc/core/EventModel.h#L229
• codal-core/inc/core/CodalConfig.h#L113

[abchatra]

@microbit-carlos what is the impact of this bug?

[microbit-carlos]

We are working around it in the extension by creating a custom onEvent TS function that calls a custom registerWithDal C++ function that passes the extra argument to uBit.messageBus.listen(). So it's not a blocker, but I would consider this a bug in pxt-microbit, as it's only missing passing the flags argument forward.

- uBit.messageBus.listen(id, event, dispatchForeground, a); 
+ uBit.messageBus.listen(id, event, dispatchForeground, a, flags);