Removes whitespace caused by the twig debug mode in Drupal 8.

readme.md

Nothing will change in Chrome Debug tool. The sourcecode might look a bit messy.

Add the following line to the extras key in your composer.json:

…
        "patches": {
            "drupal/core": {
                "Removes whitespace caused by the twig debug mode": "https://gist.githubusercontent.com/loominade/23445006f5cea2d1bfd3e95d48c8eb3d/raw/f2f8e82ecae0f86dc913588b8a6362b8a874c082/drupal-8-remove-breaks-in-debug.diff"
            }
        }
…

drupal-8-remove-breaks-in-debug.diff

--- /core/themes/engines/twig/twig.engine
+++ /core/themes/engines/twig/twig.engine
@@ -74,8 +74,8 @@
     throw $e;
   }
   if ($twig_service->isDebug()) {
-    $output['debug_prefix'] .= "\n\n<!-- THEME DEBUG -->";
-    $output['debug_prefix'] .= "\n<!-- THEME HOOK: '" . Html::escape($variables['theme_hook_original']) . "' -->";
+    $output['debug_prefix'] .= "<!-- THEME DEBUG -->";
+    $output['debug_prefix'] .= "<!-- THEME HOOK: '" . Html::escape($variables['theme_hook_original']) . "' -->";
     // If there are theme suggestions, reverse the array so more specific
     // suggestions are shown first.
     if (!empty($variables['theme_hook_suggestions'])) {
@@ -109,10 +109,10 @@
         $prefix = ($template == $current_template) ? 'x' : '*';
         $suggestion = $prefix . ' ' . $template;
       }
-      $output['debug_info'] .= "\n<!-- FILE NAME SUGGESTIONS:\n   " . Html::escape(implode("\n   ", $suggestions)) . "\n-->";
+      $output['debug_info'] .= "<!-- FILE NAME SUGGESTIONS:\n   " . Html::escape(implode("\n   ", $suggestions)) . "\n-->";
     }
-    $output['debug_info']   .= "\n<!-- BEGIN OUTPUT from '" . Html::escape($template_file) . "' -->\n";
-    $output['debug_suffix'] .= "\n<!-- END OUTPUT from '" . Html::escape($template_file) . "' -->\n\n";
+    $output['debug_info']   .= "<!-- BEGIN OUTPUT from '" . Html::escape($template_file) . "' -->";
+    $output['debug_suffix'] .= "<!-- END OUTPUT from '" . Html::escape($template_file) . "' -->";
   }
   // This output has already been rendered and is therefore considered safe.
   return Markup::create(implode('', $output));