PhutilRemarkupHexColorCodeRule: Do not assume that parameter is a string

Summary:
Check type before potentially mangling HTML in a PhutilSafeHTML element.
For now, do not try to apply this renderer when not dealing with a plain string.

Closes T15802

Test Plan: After deleting the corresponding MarkupCache via `DELETE FROM phabricator_cache.cache_markupcache WHERE cacheData LIKE "%whatever description on the page%";` check the description of a page, e.g. of `/config/edit/security.require-https/` or `/config/edit/storage.default-namespace/`.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15802

Differential Revision: https://we.phorge.it/D25605

src/infrastructure/markup/markuprule/PhutilRemarkupHexColorCodeRule.php

@@ -9,11 +9,14 @@ final class PhutilRemarkupHexColorCodeRule
 
   public function apply($text) {
     // Match {#FFFFFF}
+    if (is_string($text)) {
       return preg_replace_callback(
         '@\B\{(#([0-9a-fA-F]{3}){1,2})\}@',
         array($this, 'markupHexColorCodedText'),
         $text);
     }
+    return $text;
+  }
 
   protected function contrastingColor($color_code) {
     $match = ltrim($color_code, '#');

src/infrastructure/markup/markuprule/PhutilRemarkupRule.php

@@ -18,6 +18,12 @@ abstract class PhutilRemarkupRule extends Phobject {
     return 500.0;
   }
 
+  /**
+   * Check input whether to apply RemarkupRule. If true, apply formatting.
+   * @param  string|PhutilSafeHTML String to check and potentially format.
+   * @return string|PhutilSafeHTML Unchanged input if no match, or input after
+   * matching the formatting rule and applying the formatting.
+   */
   abstract public function apply($text);
 
   public function getPostprocessKey() {