Wordpress - Delete post with all files attached to it

I wrote the following function that uses the logic suggested by @rarst in his answer.

add_action( 'before_delete_post', function( $id ) {
  $attachments = get_attached_media( '', $id );
  foreach ($attachments as $attachment) {
    wp_delete_attachment( $attachment->ID, 'true' );
  }
} );

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IMPORTANT: Keep in mind it will only be called when the posts are permanently deleted from the trash! If you want to change this behaviour, include the following line in your wp-config.php file:

define('EMPTY_TRASH_DAYS', 0);

If this constant is set to 0, the trash functionality will be disabled and the 'Delete Permanently' button will appear instead of 'Trash' button. If you click 'Delete Permanently' button, the item will immediately be deleted without any alert message.

(From the Codex)

Expanding on other answers here for use with only a specific post type.

add_action( 'before_delete_post', 'delete_all_attached_media' );

function delete_all_attached_media( $post_id ) {

  if( get_post_type($post_id) == "post" ) {
    $attachments = get_attached_media( '', $post_id );

    foreach ($attachments as $attachment) {
      wp_delete_attachment( $attachment->ID, 'true' );
    }
  }

}

This will delete all attached media when a post is permanently deleted.

WP does not do this by default since there is no guarantee that attachment isn't still being used by some other post.

Basic logic would be to hook into delete_post, query for child attachments and run wp_delete_attachment() on each.

I did quick search in plugin repository and came up with tiny plugin that does just that (seems unmaintained so test before use) - Post Data Delete Advanced.