Is it possible to add template suggestions for image styles?

Question

I am experimenting with durpal 8 theme hook suggestions. I tried to customize the the theme suggestions based on the style name. I want the ability to add a twig template for each style if I wanted so I tried this:

function themename_theme_suggestions_image_style_alter(&$suggestions, array $variables, $hook) {
  $suggestions[] = [$hook . '__' . $variables['style_name']];
}

and

function themename_theme_suggestions_image_alter(&$suggestions, array $variables, $hook) {
  $suggestions[] = [$hook . '__' . $variables['style_name']];
}

I was expecting to see this as a theme hook suggestion in the html comments printed by in the page source after enabling twig debuging.

Using xdebug the hook is triggered but I don't find it in the suggestions list in the html after enabling twig.config.debug to true.

am I missing anything?

Answer 1

1. hook_theme_suggestions_HOOK_alter doesn't use a third argument.
2. You are supposed to add the suggestions as string.

---

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function MYTHEME_theme_suggestions_image_style_alter(array &$suggestions, array $variables) {
  $suggestions[] = $variables['theme_hook_original'] . '__' . $variables['style_name'];
}

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function MYTHEME_theme_suggestions_image_alter(array &$suggestions, array $variables) {
  $suggestions[] = $variables['theme_hook_original'] . '__' . $variables['style_name'];
}