Issue #1843034 by Cottser, japerry, heyrocker, steveoliver, c4rl: Make Twig settings configurable.

core/lib/Drupal/Core/CoreBundle.php

@@ -368,7 +368,7 @@ protected function registerTwig(ContainerBuilder $container) {
         // This is saved / loaded via drupal_php_storage().
         // All files can be refreshed by clearing caches.
         // @todo ensure garbage collection of expired files.
-        'cache' => TRUE,
+        'cache' => settings()->get('twig_cache', TRUE),
         'base_template_class' => 'Drupal\Core\Template\TwigTemplate',
         // @todo Remove in followup issue
         // @see http://drupal.org/node/1712444.
@@ -376,10 +376,8 @@ protected function registerTwig(ContainerBuilder $container) {
         // @todo Remove in followup issue
         // @see http://drupal.org/node/1806538.
         'strict_variables' => FALSE,
-        // @todo Maybe make debug mode dependent on "production mode" setting.
-        'debug' => TRUE,
-        // @todo Make auto reload mode dependent on "production mode" setting.
-        'auto_reload' => FALSE,
+        'debug' => settings()->get('twig_debug', FALSE),
+        'auto_reload' => settings()->get('twig_auto_reload', NULL),
       ))
       ->addMethodCall('addExtension', array(new Definition('Drupal\Core\Template\TwigExtension')))
       // @todo Figure out what to do about debugging functions.

sites/default/default.settings.php

@@ -283,6 +283,42 @@
  */
 $settings['update_free_access'] = FALSE;
 
+/**
+ * Twig debugging:
+ *
+ * When enabled, you can use the 'dump' function in Twig templates to output
+ * information about variables, and templates are automatically recompiled
+ * whenever the source code changes.
+ *
+ * @see http://drupal.org/node/1906392
+ *
+ * Not recommended in production environments (Default: FALSE).
+ */
+# $settings['twig_debug'] = TRUE;
+
+/**
+ * Twig auto-reload:
+ *
+ * Automatically recompile Twig templates whenever the source code changes. If
+ * you don't provide a value for twig_auto_reload, it will be determined based
+ * on the value of twig_debug.
+ *
+ * Not recommended in production environments (Default: NULL).
+ */
+# $settings['twig_auto_reload'] = TRUE;
+
+/**
+ * Twig cache:
+ *
+ * By default, Twig templates will be compiled and stored in the filesystem to
+ * increase performance. Disabling the Twig cache will recompile the templates
+ * from source each time they are used. In most cases the twig_auto_reload
+ * setting above should be enabled rather than disabling the Twig cache.
+ *
+ * Not recommended in production environments (Default: TRUE).
+ */
+# $settings['twig_cache'] = FALSE;
+
 /**
  * External access proxy settings:
  *