Add cookbook chapter on error_bubbling and dealing with form errors in twig

[webdevilopers]

@weaverryan from @KnpLabs posted a nice article here:
https://knpuniversity.com/blog/symfony-debugging-form-errors

Originally I came from the following issue: symfony/symfony#17363

The described issue caused a strange effect in which non mapped field errors were linked to the parent form - the same thing that would have happened if you turned error_bubbling to true.

Since this I was able to catch the errors from the form.vars array in my template:

{% if form.vars.errors|length > 0 %}

After i solved the issue the errors were correctly removed from the bubble and attached to the assigned field. My twig condition would no longer work. I had to change it:

{% if not form.vars.valid %}

I've seen a lot of questions on SO on this e.g.:

• http://stackoverflow.com/questions/8914649/simple-check-if-form-field-has-errors-in-twig-template @lstrojny
• http://stackoverflow.com/questions/22650127/form-errorsform-symfony2-twig
  etc.

Actually I havn't found any chapter that explains what error_bubbling is in the first place.
Most of the times it is described directly inside a form field type or collection.

I think the cookbook could really be improved with this. What do you think?

[carsonbot]

Thank you for this issue.
There has not been a lot of activity here for a while. Has this been resolved?

[carsonbot]

Friendly ping? Should this still be open? I will close if I don't hear anything.

[webdevilopers]

I'm no longer working with the Form component. Closing.