Issue #1939082 by shanethehat, larowlan, jenlampton, Cottser, LewisNyman, duellj, Mark Carver, joelpittet: Convert theme_status_messages() to Twig.

core/includes/theme.inc

@@ -1572,44 +1572,22 @@ function template_preprocess_datetime(&$variables) {
 }
 
 /**
- * Returns HTML for status and/or error messages, grouped by type.
+ * Prepares variables for status message templates.
  *
- * An invisible heading identifies the messages for assistive technology.
- * Sighted users see a colored box. See http://www.w3.org/TR/WCAG-TECHS/H69.html
- * for info.
+ * Default template: status-messages.html.twig.
  *
- * @param $variables
+ * @param array $variables
  *   An associative array containing:
- *   - display: (optional) Set to 'status' or 'error' to display only messages
- *     of that type.
+ *   - display: (optional) May have a value of 'status' or 'error' when only
+ *     displaying messages of that specific type.
  */
-function theme_status_messages($variables) {
-  $display = $variables['display'];
-  $output = '';
-
-  $status_heading = array(
+function template_preprocess_status_messages(&$variables) {
+  $variables['message_list'] = drupal_get_messages($variables['display']);
+  $variables['status_headings'] = array(
     'status' => t('Status message'),
     'error' => t('Error message'),
     'warning' => t('Warning message'),
   );
-  foreach (drupal_get_messages($display) as $type => $messages) {
-    $output .= "<div class=\"messages messages--$type\">\n";
-    if (!empty($status_heading[$type])) {
-      $output .= '<h2 class="visually-hidden">' . $status_heading[$type] . "</h2>\n";
-    }
-    if (count($messages) > 1) {
-      $output .= " <ul class=\"messages__list\">\n";
-      foreach ($messages as $message) {
-        $output .= '  <li class="messages__item">' . $message . "</li>\n";
-      }
-      $output .= " </ul>\n";
-    }
-    else {
-      $output .= $messages[0];
-    }
-    $output .= "</div>\n";
-  }
-  return $output;
 }
 
 /**
@@ -3032,6 +3010,7 @@ function drupal_common_theme() {
     ),
     'status_messages' => array(
       'variables' => array('display' => NULL),
+      'template' => 'status-messages',
     ),
     'links' => array(
       'variables' => array('links' => array(), 'attributes' => array('class' => array('links')), 'heading' => array()),

core/modules/system/templates/status-messages.html.twig

@@ -0,0 +1,38 @@
+{#
+/**
+ * @file
+ * Default theme implementation for status messages.
+ *
+ * Displays status, error, and warning messages, grouped by type.
+ *
+ * An invisible heading identifies the messages for assistive technology.
+ * Sighted users see a colored box. See http://www.w3.org/TR/WCAG-TECHS/H69.html
+ * for info.
+ *
+ * Available variables:
+ * - message_list: List of messages to be displayed, grouped by type.
+ * - status_headings: List of all status types.
+ * - display: (optional) May have a value of 'status' or 'error' when only
+ *   displaying messages of that specific type.
+ *
+ * @see template_preprocess_status_messages()
+ *
+ * @ingroup themeable
+ */
+#}
+{% for type, messages in message_list %}
+  <div class="messages messages--{{ type }}">
+    {% if status_headings[type] %}
+      <h2 class="visually-hidden">{{ status_headings[type] }}</h2>
+    {% endif %}
+    {% if messages|length > 1 %}
+      <ul class="messages__list">
+        {% for message in messages %}
+          <li class="messages__item">{{ message }}</li>
+        {% endfor %}
+      </ul>
+    {% else %}
+      {{ messages.0 }}
+    {% endif %}
+  </div>
+{% endfor %}