edlp_d8/sites/all/themes/custom/edlptheme/edlptheme.theme

<?php

/**
 * @file
 * Functions to support theming in the edlp theme.
 */


use Drupal\Core\Form\FormStateInterface;

// function edlptheme_preprocess_input(&$vars){
  // dsm($vars, 'vars');
  // $vars['attributes']['placeholder'] = "salut";
// }

/**
 * Implements hook_form_alter
 */
function edlptheme_form_user_login_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  // dpm($form_id, 'form_id');
  // dpm($form, 'form');
  $form['name']['#attributes']['placeholder'] = (string) $form['name']['#title'];
  unset($form['name']['#title']);
  $form['pass']['#attributes']['placeholder'] = (string) $form['pass']['#title'];
  unset($form['pass']['#title']);
}