Issue #1798880 by andyceo, LinL, mtunay: Convert teaser_length() to use configuration system.

core/modules/field/modules/text/config/text.settings.yml

+default_summary_length: 600

core/modules/field/modules/text/text.install

@@ -65,3 +65,14 @@ function text_field_schema($field) {
     ),
   );
 }
+
+/**
+ * Moves teaser length from variable to config.
+ *
+ * @ingroup config_upgrade
+ */
+function text_update_8000() {
+  update_variables_to_config('text.settings', array(
+    'teaser_length' => 'default_summary_length',
+  ));
+}

core/modules/field/modules/text/text.module

@@ -229,9 +229,7 @@ function _text_sanitize($instance, $langcode, $item, $column) {
 function text_summary($text, $format = NULL, $size = NULL) {
 
   if (!isset($size)) {
-    // What used to be called 'teaser' is now called 'summary', but
-    // the variable 'teaser_length' is preserved for backwards compatibility.
-    $size = variable_get('teaser_length', 600);
+    $size = config('text.settings')->get('default_summary_length');
   }
 
   // Find where the delimiter is in the body