I'm upgrading one of my bundles to the new version 3 standard and came across this bug.

Within my FormType, I add child types like so:

$builder->add('type', new SelectType(), array(
    'choices' => array_combine($choices, static::$defaultChoices),
    'required' => true,
    'data' => self::INCLUSIVE,
    'options' => array(
        'width' => 'auto',
    ),
));

The documentation for FormBuilder::add states that the second parameter $type accepts string|FormTypeInterface. But, stepping through the code, I see the child is added to the $unresolvedChildren array. Later when getForm is called, each of these children are resolved by passing that type to FormFactory::createNamedBuilder, which expects a string.

I don't know if this is a documentation error or in fact a bug in the code. I would prefer to pass in an instance of the child type since I can construct it accordingly. Using strings and services would be a pain.