Show the default value in Config.

Summary:
As mentioned by @epriestley in an inline on D4290, we should show what happens
if the user leaves the box blank.

Test Plan: Went to edit a setting and saw the default below the text box.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, asherkin

Differential Revision: https://secure.phabricator.com/D4293

src/applications/config/controller/PhabricatorConfigController.php

@@ -24,4 +24,20 @@ abstract class PhabricatorConfigController extends PhabricatorController {
     return $crumbs;
   }
 
+  /**
+   * Properly format a JSON value.
+   *
+   * @param wild Any value, but should be a raw value, not a string of JSON.
+   * @return string
+   */
+  public function prettyPrintJSON($value) {
+    // Check not only that it's an array, but that it's an "unnatural" array
+    // meaning that the keys aren't 0 -> size_of_array.
+    if (is_array($value) && array_keys($value) != range(0, count($value) - 1)) {
+      return id(new PhutilJSON())->encodeFormatted($value);
+    } else {
+      return json_encode($value);
+    }
+  }
+
 }