Debug 404 page

Following code dump state of #WordPress 404 page with permalins, rewrite rules etc. plase it to functions.php

ini_set('error_reporting', -1);
ini_set('display_errors', 'On');

add_action(
  'parse_request',
  function (&$wp) {
    global $wp_rewrite;

    printf('<h2>rewrite rules</h2><pre>%s</pre>', var_export($wp_rewrite->wp_rewrite_rules(), true));

    printf('<h2>permalink structure</h2><pre>%s</pre>', var_export($wp_rewrite->permalink_structure, true));

    printf('<h2>page permastruct</h2><pre>%s</pre>', var_export($wp_rewrite->get_page_permastruct(), true));
    printf('<h2>matched rule and query</h2><pre>%s</pre>', var_export($wp->matched_rule, true));
    printf('<h2>matched query</h2><pre>%s</pre>', var_export($wp->matched_query, true));
    printf('<h2>request</h2><pre>%s</pre>', var_export($wp->request, true));

    global $wp_the_query;
    printf('<h2>the query</h2><pre>%s</pre>', var_export($wp_the_query, true));
  }
);

add_action(
  'template_redirect',
  function () {
    global $wp_filter;
    printf(
      '<h2>template redirect filters</h2><pre>%s</pre>',
      var_export($wp_filter[current_filter()], true)
    );
  }, 99999
);

add_filter(
  'template_include',
  function ($template) {

    printf(
      '<h2>template file selected</h2><pre>%s</pre>',
      var_export($template, true)
    );
    exit();
  }
);