How to add a boolen attribute to a form?

Question

I am trying to add the boolean attribute "novalidate" to all my forms.

I have tried numerous approaches in my theme_preprocess_form function but no luck. I see in some preprocess functions, $variables['attribute'] is an object and has methods like addClass() and setAttribute(). But in _preprocess_form it is an array. Plus setAttribute doesnt sound like it will do boolean attributes anyway.

I tried to simply override the twig template for a form and do this:

<form{{ attributes }} novalidate>
  {{ children }}
</form>

but even that outputs:

<form novalidate="">

Answer 1

You may be attempting to solve a non-issue here. novalidate="" is fine for the HTML spec - boolean attributes can have a value as long as it's an empty string or the same (case-insensitive) string as the attribute name. So novalidate="novalidate" would also be fine.

If you follow those rules, the attribute's existence is taken to mean true, regardless of the value.

See https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes#boolean_attributes for more info.