Validation group not applied correctly when validating a CollectionInputFilter

[weierophinney]

While debugging a problem when validating a complex form containing collections and validation groups to limit the fields that are being validated I notice the following code in CollectionInputFilter:

        foreach ($this->data as $key => $data) {
            // ....
            if (null !== $this->validationGroup) {
                $inputFilter->setValidationGroup($this->validationGroup[$key]);
            }

If the CollectionInputFilter has a validation group then the validation group is indexed using the same key as the data. A validation group is assigned like this:

$collection = new CollectionInputFilter(...);
$collection->setValidationGroup(array(
    'a', 'b', 'c'
));

Now, for the first element in the list only property a is validated, property b for the second, etc.

Am I missing something in the way I assign my validation group? Or should the line where the validation group is assigned read:

                $inputFilter->setValidationGroup($this->validationGroup);

I can work around this by calling $collection->getInputFilter()->setValidationGroup(...) instead, however this prevents me of performing a single setValidationGroup call at the root of my form with a single nested array for the entire form.

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Originally posted by @erikorbons at zendframework/zend-inputfilter#113

[weierophinney]

Yep really strange, but can be used like this:

$inputFilter = new InputFilter();
$inputFilter->add([
    'name' => 'foo',
    'required' => true,
]);
$inputFilter->add([
    'name' => 'bar',
    'required' => true,
]);

$collection = new CollectionInputFilter();
$collection->setInputFilter($inputFilter);
$collection->setValidationGroup([0 => ['bar'], 1 => ['foo']]);

$collection->setData([
    0 => ['bar' => 'value'], // valid because only 'bar' in validation group
    1 => ['foo' => 'value2'] // valid because only 'foo' in validation group
]);
$collection->isValid();

Okay I am not sure this is desired behavior nor use case for this, but well can't think otherwise why setValidationGroup() is called in every foreach loop. And also there is a test for this so can't be fixed?
also data being array of 3 elements will throw Undefined offset: 2

@weierophinney what do you think? If this is a bug I can create PR with a fix.

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Originally posted by @svycka at zendframework/zend-inputfilter#113 (comment)