Support entities without bundles (User, etc.)

This is what worked for me:

Apply the patch in #19

In the .module file for my custom entity module I added the following:

/**
 * Implements hook_entity_type_alter().
 */
function mymodule_entity_type_alter(array &$entity_types) {

  /** @var \Drupal\Core\Entity\EntityTypeInterface[] $entity_types */
  $entity_types['my_entity']->setLinkTemplate('auto-label', '/admin/structure/my_entity/settings/auto-label');

}

Replacing mymodule with the name of your module and my_entity with the name of the entity (and any other changes to the path to match where your entity admin lives.

I just added this and this worked for me:

function mymodule_entity_type_alter(array &$entity_types): void {
  /** @var EntityTypeInterface[] $entity_types */
  $entity_types['my_entity']->setLinkTemplate('auto-label', '/admin/structure/my_entity/auto-label');
}

Including "/settings" did not work.

Though if you are a developer and using custom entities then you should have access to the entity configuration so you just need to add this:

 *   links = {
 *     "canonical" = "/admin/structure/my_entity/{my_entity}",
 *     "add-form" = "/admin/structure/my_entity/add",
 *     "edit-form" = "/admin/structure/my_entity/{my_entity}/edit",
 *     "delete-form" = "/admin/structure/my_entity/{my_entity}/delete",
 *     "collection" = "/admin/structure/my_entity",
 *     "auto-label" = "/admin/structure/my_entity/auto-label",
 *   },

which is a lot cleaner.

For custom entities #19 and #23 made the job.

Potentially major problem with the else statement in this block of code:

    // Special treatment for Core's user entity.
    if ($entity_type_id == 'user') {
      $widget = &$form['account']['name'];
    }
    else {
      $widget = &$form[$label]['widget'][0]['value'];
    }

Not all entity form displays are going to have a label field in the form. Assigning a non-existent form element to $widget by reference actually created the element with a value of null;

Problem is that ContentEntityForm::copyFormValuesToEntity then gets called and because the label widget was added to the form (with a value of null), ::copyFormValuesToEntity then sets the label to be null.

This is probably a problem only when auto_entitylabel is disabled for a particular entity type and when the label widget is not present in the form currently being submitted.

Setting back to "Needs review"

Re-rolled patch from #19 against latest 8.x-3.x branch. The existing patch no longer applied after the latest changes included in the 8.x-3.2 release.