Restricted values for `getBlockPrefix` in symfony 4 - forms

Question

I'm building a simple CRUD using symfony 4.
One of my entities is called Color. Nothing fancy about it. It just has 4 properties: name, description, sortOrder and id (PK).
I also built a form class to be able to add/edit my entity instances.
The form looks like this:
<?php
namespace App\Form;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\IntegerType;
use Symfony\Component\Form\Extension\Core\Type\TextareaType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\Extension\Core\Type\HiddenType;
class Color extends AbstractType
{
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('id', HiddenType::class)
->add('name', TextType::class)
->add('description', TextareaType::class, ['required' => false])
->add('sort_order', IntegerType::class);
}
}
When I try to render the form I get an error
An exception has been thrown during the rendering of a template ("Catchable Fatal Error: Object of class App\Entity\Color could not be converted to string").
I have other forms that look similar and they work.
If I don't let symfony decide the block prefix based on the class name and add the method
public function getBlockPrefix()
{
return 'anything-else-but-color';
}
then the form is rendered.
I don't want to do that because my app is kind of "convention" based and I need a match between the entity class name and the form name.
I know I can change both the entity and the form class names (and I'm probably going to do that) but this bugs me because I don't know what happens and if there are any other reserved words that might screw up my app.
Additional info...
I can partially debug this.
I see that when the form is rendered something like this is generated
<input type="color" id="color" name="color" class="form-control" ....
(notice the type color).
For a different entity and form built in the same way (named group) I get this rendered in the same place as above.
<div id="group">...
So my questions are:
Are there any reserved words that cannot be used for getBlockPrefix in a form?
Can I use the word color as a block prefix without jumping through many hoops?

Answer 1

The documentation touches on this:
When the name of your form class matches any of the built-in field
types, your form might not be rendered correctly. A form type named
App\Form\PasswordType will have the same block name as the built-in
PasswordType and won't be rendered correctly. Override the
getBlockPrefix() method to return a unique block prefix (e.g.
app_password) to avoid collisions.
I would have expected this to trigger if your form type was called ColorType however, for completeness sake as per your comment:
I think it crashes for me because the Type at the end of the class
name is ignored.
StringUtil::fqcnToBlockPrefix('Symfony\Component\Form\Extension\Core\Type\ColorType');
and StringUtil::fqcnToBlockPrefix('Whatever\YouWant\Color'); return
the same thing: color