How do I programmatically disable a form?

Question

I want disable the user register form depending some conditions. The user go to the "/user/register" page, and he must see 'Registration is disable because ...'.

From my "form_user_register_form_alter" hook, I don't find anywhere how can I disable all the form programmatically (I mean removing all fields form). I think I can unset all form elements, but I feel that is an ugly way.

Is there a method (from the FormStateInterface class) or a Drupal function (for the form variable) to properly disable the form?

This is my most recent tentative.

function mycustommodule_limit_form_user_register_form_alter(&$form, FormStateInterface $form_state){
  if (...) {
    $form['#access'] = FALSE; // Drupal 7 (ugly?) way
    drupal_set_message('This form is disable because...');
  }
}

When I go to the /user/register form, the form is disable ! but I get this error.

Notice: Undefined index: #markup in Drupal\Core\Render\RenderCache->getCacheableRenderArray() (line 323 of core/lib/Drupal/Core/Render/RenderCache.php).

I would like to hide/remove Create new account too.

Answer 1

The D8 way to do this is to write a custom access check.

This is the one which now checks the access for the user register form:

src/Access/RegisterAccessCheck.php

<?php

namespace Drupal\user\Access;

use Drupal\Core\Access\AccessResult;
use Drupal\Core\Routing\Access\AccessInterface;
use Drupal\Core\Session\AccountInterface;

/**
 * Access check for user registration routes.
 */
class RegisterAccessCheck implements AccessInterface {

  /**
   * Checks access.
   *
   * @param \Drupal\Core\Session\AccountInterface $account
   *   The currently logged in account.
   *
   * @return \Drupal\Core\Access\AccessResultInterface
   *   The access result.
   */
  public function access(AccountInterface $account) {
    $user_settings = \Drupal::config('user.settings');
    return AccessResult::allowedIf($account->isAnonymous() && $user_settings->get('register') != USER_REGISTER_ADMINISTRATORS_ONLY)->cacheUntilConfigurationChanges($user_settings);
  }

}

user.services.yml

services:
  access_check.user.register:
    class: Drupal\user\Access\RegisterAccessCheck
    tags:
      - { name: access_check, applies_to: _access_user_register }

user.routing.yml

user.register:
  path: '/user/register'
  defaults:
    _entity_form: 'user.register'
    _title: 'Create new account'
  requirements:
    _access_user_register: 'TRUE'

Put these files in a module and change user to mymodule and choose a custom class name.

To successfully override the route in mymodule.routing.yml you have to adjust the module weight. Or instead change the access settings of the existing route in a RouteSubscriber, which is a bit more work to do, but the better solution.

Answer 2

A simple way to do it in Drupal 8 hook_form_alter:

$form = [
  '#parents' => [],
  '#markup' => t('Access Denied.'),
];

If you have errors with the above solution, you can try to modify an existing form:

  $form['#access'] = FALSE;
  $form['#markup'] = t('Access Denied.');
  $form['#cache'] = [
    'contexts' => [],
    'max-age' => 0,
  ];

Answer 3

You can create a form template and show a form or some markup according to some conditions. In your_theme.theme or your_module.module file add this:

/**
 * Implements hook_theme().
 */
function your_theme_theme($existing, $type, $theme, $path) {
  $theme = array('user_register_form' =>
          array(
    'render element' => 'form',
    'path' => drupal_get_path('theme', 'your_theme') . '/templates',
    'template' => 'user-register-form'
  ));
}

Create user-register-form.html.twig.

Define some condition (it is just for example as i don't know how and what condition you want to add) in hook_form_FORM_ID_alter

function your_theme_form_YOUR_FORM_ID_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  if ($some_variable == 'some condition') {
       $form['condition'] = TRUE;
   }

}

In your template file:

{% if form.condition %}

<p>Registration is disable because ..</p>

{% else %}
   {{ form.some_field_1 }} 
   {{ form.some_field_2 }} 
   {{ form }}
{% endif %}