merging attributes

theme.inc

      $variables['attributes']['class'] = 'test-attribute-merge-1';
      $variables['content_attributes']['class'] ='test-content_attributes-merge-2';

      $variables['attributes']['role'] = 'attributes-role';
      $variables['content_attributes']['role'] = 'content_attributes-role';

      $variables['title_attributes']['role'] = 'title-attributes-role';
      $variables['item_attributes']['0']['role'] = 'item-attributes-role';

      //wtf why u not merge 
      $variables['attributes_test'] = NestedArray::mergeDeepArray(array(
          $variables['attributes'],
          $variables['content_attributes'],
          $variables['title_attributes']
        )
      );

What do you expect as result? Same keys will override with priority to the last given argument. You won't get a joined 'roles' key with all roles that you assigned if that is what you are looking for.

At least that is what I get from a quick look at the method.

yup thats exactly what i was getting

Now I don't know the Drupal API but my guess is that there is no method for what you need. Would be pretty useful for a web CMS that has to deal with HTML attributes. :)

Edit: Rereading this might come over a bit unfriendly but isn't meant that way. This kind of merging is pretty difficult because it's hard to define what you expect. Basically for this kind of merging you can only reasonably work with one level of nesting.