[html-formfu] Can't programatically add constraint or validator callbacks (unless I call $form->process)

[Dan Dascalescu]

As a new FormFu user, I saw that I could modify the form before it got rendered:

sub index :Path :Args(0) :FormConfig {
   my ( $self, $c ) = @_;
   my $form = $c->stash->{form};

   my $field = $form->get_all_element({name => 'foo'});
   $field->label('new label');  # this works

   if ( $form->submitted_and_valid ) {
   ... the usual
   }
}

However, the same is not true of constraints. Adding the code below to
the index sub, before if ( $form->submitted_and_valid ), has no
effect:

   $field->constraint({
       type => 'Callback',
       callback => \&never_gets_called,
   });

   $field->validator('Callback')->callback( \&never_gets_called );

I believe another user encountered the same problem:
http://www.mail-archive.com/html-formfu@lists.scsys.co.uk/msg00970.html

There are two workarounds:
1. Add the constraint in the form config file
2. Call $form->process before $form->submitted_and_valid. This is
really counter-intuitive to new users: since $field->label works
without $form->process, why would $field->validator need a
$form->process?

If form->process() really needs to be called for callbacks to get
registered, then maybe the doc for process() should mention this.

HTH,
Dan