Tag for custom post type

Question

I have several post type (animal, science, car), I want all these posts type to use the same Wordpress default tag. exemple of car post type :

    // custom post type

add_action( 'init', 'create_post_type' );
function create_post_type() {
  register_post_type( 'car',
    array(
      'labels' => array(
        'name' => __( 'Car' ),
        'add_new_item' => 'Ajouter une voiture',
        'edit_item' => 'Modifier une voiture',
        'new_item' => 'Ajouter une voiture',
        'singular_name' => __( 'car' )
      ),
      'public' => true
    )
  );
register_taxonomy( 'categorycar', 'car', array( 'hierarchical' => true, 'label' => 'Category voiture', 'query_var' => true, 'rewrite' => true ) );

i use a custom category different of each post type and i want use default tag wordpress for all post type.

Thanks for your help.

Answer 1

Use taxonomies parameter when registering custom post type:

register_post_type( 'car',
    [
        'labels' => [ /* ... */ ],
        'public' => true,
        'taxonomies' => [ 'post_tag', 'categorycar' ],  
    ]
);

Or, after registering post types, use register_taxonomy_for_object_type() function.

register_post_type( 'animal',  /* ... */ );
register_post_type( 'science', /* ... */ );

register_taxonomy_for_object_type( 'post_tag', 'animal' );
register_taxonomy_for_object_type( 'post_tag', 'science' );