ZF2 : Filedset validation is not working

Frankly, this type of problem is why I always build a separate InputFilter hierarchy matching the Form structure instead of relying on ZF's "magic" input filter builder. Here's a great article on how to do that:

• http://circlical.com/blog/2015/7/6/zend-framework-2-forms-factories-inputfilters-and-hydration

When working with collections in this manner you'll need to add a CollectionInputFilter to the form's input filter for each Collection form element. That class is completely undocumented IIRC, but you can find an example here and the class here.

I wrote a short script that reproduces what you're seeing:

<?php
<<<CONFIG
packages:
    - "zendframework/zend-form: ^2.0"
    - "zendframework/zend-servicemanager: ^3.0"
    - "zendframework/zend-hydrator: ^2.0"
CONFIG;
// Run this script with Melody: http://melody.sensiolabs.org/


use Zend\Form\Fieldset;
use Zend\InputFilter\InputFilterProviderInterface;
use Zend\Form\Form;

class ChildFieldset extends Fieldset implements InputFilterProviderInterface
{
    public function __construct($name = null, $options = array())
    {
    parent::__construct($name, $options);

    $this->add(array(
        'name' => 'fieldA',
        'type' => 'text',
        'attributes' => array(
            'id' => 'fieldA',
        ),
        'options' => array(
            'label' => 'Field A',
        )
    ));
    }

    public function getInputFilterSpecification()
    {
    return array(
        'fieldA' => array(
            'required'          => true,
            'allow_empty'       => false,
            'continue_if_empty' => false,
            'filters' => array(
                array('name' => 'StringTrim')
            ),
            'validators' => array(
                array('name' => 'NotEmpty')
            )
        ),
    );
    }
}

class ParentForm extends Form
{
    public function __construct($name, array $options)
    {
    parent::__construct($name, $options);

    $this->add(array(
        'type' => 'Zend\Form\Element\Collection',
        'name' => 'childForms',
        'options' => array(
            'label' => 'Child Forms',
            'allow_add' => true,
            'should_create_template' => true,
            'template_placeholder' => '__placeholder__',
            'target_element' => array(
                'type' => 'ChildFieldset',
            ),
        ),
    ));

    $this->add(array(
        'name' => 'submit',
        'attributes' => array(
            'type' => 'submit',
            'value' => 'Save',
        )
    ));
    }
}

$form = new ParentForm('foo', []);

$data = [];
$form->setData($data);
echo "Dataset: " . print_r($data, true) . "\n";
echo "Result: " . ($form->isValid() ? 'valid' : 'invalid');
echo "\n\n--------------------------------------\n\n";


$data = [
    'childForms' => []
];
$form->setData($data);
echo "Dataset: " . print_r($data, true) . "\n";
echo "Result: " . ($form->isValid() ? 'valid' : 'invalid');
echo "\n\n--------------------------------------\n\n";


$data = [
    'childForms' => [
    ['fieldA' => ''],
    ],
];
$form->setData($data);
echo "Dataset: " . print_r($data, true) . "\n";
echo "Result: " . ($form->isValid() ? 'valid' : 'invalid') . "\n\n";
echo "\n\n--------------------------------------\n\n";


$data = [
    'childForms' => [
    ['fieldA' => 'fff'],
    ],
];
$form->setData($data);
echo "Dataset: " . print_r($data, true) . "\n";
echo "Result: " . ($form->isValid() ? 'valid' : 'invalid') . "\n\n";

and when I run it (PHP 7.0.9) I get this:

Dataset: Array
(
)

Result: valid
(wrong)

--------------------------------------

Dataset: Array
(
    [childForms] => Array
    (
    )

)

Result: valid
(wrong)

--------------------------------------

Dataset: Array
(
    [childForms] => Array
    (
        [0] => Array
            (
                [fieldA] => 
            )

    )

)

Result: invalid
(correct!)


--------------------------------------

Dataset: Array
(
    [childForms] => Array
    (
        [0] => Array
            (
                [fieldA] => fff
            )

    )

)

Result: valid
(correct!)

The input filter on the child fieldset is only triggered when the full hierarchy of keys exist in the data. It's not a bug per se, but it's not what you expect to happen.