Twig configuration settings and debug output

The core implementation of Twig now supports container parameters to enable debugging, auto-reloading templates, and caching compiled templates. The following container parameters are set in sites/example.com/services.yml by default:

parameters:
  twig.config:
    debug: false
    auto_reload: null
    cache: true

Note that if twig_debug is set to true, then twig_auto_reload also defaults to true unless it is explicitly set otherwise.


With debugging enabled, Twig templates will be wrapped with HTML comments like so:

<!-- THEME DEBUG -->
<!-- CALL: theme('node') -->
<!-- FILE NAME SUGGESTIONS:
   * node--article.html.twig
   * node--2.html.twig
   x node.html.twig
-->
<!-- BEGIN OUTPUT from 'core/modules/node/templates/node.html.twig' -->
<article id="node-1" class="node node-article promoted view-mode-full clearfix" role="article" about="/node/1" typeof="sioc:Item foaf:Document">
  <p>(content)</p>
</article>

<!-- END OUTPUT from 'core/modules/node/templates/node.html.twig' -->

This output should help themers determine which template is being rendered, which theme suggestions are available and which theme and/or template suggestion has been selected for each piece of theme output.