This is not a mistake, the message is right and the exception is justified, cf the doc of form events (http://symfony.com/doc/current/form/events.html) and especially this warning :

During FormEvents::PRE_SET_DATA, Form::setData() is locked and will throw an exception if used. If you wish to modify data, you should use FormEvent::setData() instead.

Ok, makes sense. but maybe it should be clarified which setData is meant in the first place.

P.S. I got this when I called $event->getForm()->getData();

Ok I see exactly the problem and you are right, the message is not logic for the DX.

That happens when no data was set when the form is built, and then you use $event->getForm()->getData(); in a FormEvents::PRE_SET_DATA event. I think the right way is to use $event->getData() in this event but there is no message about this.

When you try to get the data directly from the form, as it was not set, it tries to set the default data with a Form::setData() call that will dispatch the FormEvents::PRE_SET_DATA event once again and end up in a cycle...

We can throw another exception with a better message.

That also mean that if no data was already set for the form, in a FormEvents::PRE_SET_DATA event, we cannot have access to the Form::getNormData() and Form::getViewData() methods as they also call the FormEvent::setData() and will throw the same misleading exception.

well, getting the data from the form before it is set in it does not make any sense anyway. It is not there yet.

I agree but the problem is that if you try to do it, you get a misleading / unrelated message.

We are always in favor of improving error messages, so would @desmax or @fancyweb be interested in contributing a pull request to improve this error message a little? Thanks!

@javiereguiluz I will work on improving this.