Adding Twig Template Suggestions for Form Elements

By Kevin Quillen, on January 28, 2017

Last week, I had to solve a problem where a prototyped form contained a button element and svg icon for the submit button on three search forms.

While you can change the type of a input from submit to button in Drupal 8, that does not change the tag the form element uses.

I needed a clean solution that allowed me to provide the markup and svg icon without interfering with the function of the form itself.

Here is the output I needed to achieve:


<button type="button" class="search-box__button">
  <svg class="icon search-box__open">
    <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/build/img/svg-sprite.svg#icon-search"></use>
  </svg>
</button>

I did a little digging, and saw that Drupal base theme (classy or stable) provide an input.html.twig and the option of overriding an element with input--(type).html.twig. That’s cool, but I don’t want to override all submits on the website, just specific ones.

Fortunately, core provides many ways to hook in and provide more template suggestions if none suit. I had the idea to add a data-attribute on my form element that I wanted to override. Then, using hook_theme_suggestions_input_alter(), I look to see if this attribute exists, if so, create the suggestion based on that value.

Here it is in action:


/**
 * @param $suggestions
 * @param array $variables
 */
function mytheme_theme_suggestions_input_alter(&$suggestions, array $variables) {
  $element = $variables['element'];

  if (isset($element['#attributes']['data-twig-suggestion'])) {
    $suggestions[] = 'input__' . $element['#type'] . '__' . $element['#attributes']['data-twig-suggestion'];
  }
}

/**
 * @param $form
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 * @param $form_id
 */
function mytheme_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if ($form['#id'] == 'views-exposed-form-search-results') {  
    $form['actions']['submit']['#attributes']['data-twig-suggestion'] = 'search_results_submit';
    $form['actions']['submit']['#attributes']['class'][] = 'search-box__button';
  }
}

I simply use the #attributes key to add my data attribute. Originally, I was using the #name key only, but I figured I would create my own data attribute so nothing else in the system interferes with it, and I can guarantee uniqueness if multiple exist on the page.

Then, I created the necessary twig file. In this case, it is input--submit--search-results-submit.html.twig:


{#
/**
 * @file
 * Theme override for an 'input' #type form element.
 *
 * Available variables:
 * - attributes: A list of HTML attributes for the input element.
 * - children: Optional additional rendered elements.
 *
 * @see template_preprocess_input()
 */
#}
<button{{ attributes }}>
  <svg class="icon search-box__open">
    <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/themes/custom/mytheme/build/img/svg-sprite.svg#icon-search"></use>
  </svg>
</button>

Now, if I want to apply the same treatment to other submit buttons, I simply pop that data attribute on the end and reload the page.

I suppose you could also create custom theme hooks for this, and I wonder if that is more “proper”, but all in all this only took about 10 minutes to put together and gives me the ability to scale out if I need to change how elements are marked up in the future. I assume that if my needs became more complex, a theme hook would be necessary - but for now, I don’t think that it is.

Tagged with: twig, theming, templates
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