Fix regexp issue with Diffusion remarkup rule

Summary: My `\w` shenanigans don't work with Diffusion, which has no explicit prefix.

Test Plan: Typed `rXnnn` and got the whole thing properly marked up.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D5984

src/applications/diffusion/remarkup/DiffusionRemarkupRule.php

@@ -7,6 +7,10 @@ final class DiffusionRemarkupRule
     return '';
   }
 
+  protected function getObjectNamePrefixBeginsWithWordCharacter() {
+    return true;
+  }
+
   protected function getObjectIDPattern() {
     $min_unqualified = PhabricatorRepository::MINIMUM_UNQUALIFIED_HASH;
     $min_qualified   = PhabricatorRepository::MINIMUM_QUALIFIED_HASH;

src/infrastructure/markup/rule/PhabricatorRemarkupRuleObject.php

@@ -11,6 +11,11 @@ abstract class PhabricatorRemarkupRuleObject
   abstract protected function getObjectNamePrefix();
   abstract protected function loadObjects(array $ids);
 
+  protected function getObjectNamePrefixBeginsWithWordCharacter() {
+    $prefix = $this->getObjectNamePrefix();
+    return preg_match('/^\w/', $prefix);
+  }
+
   protected function getObjectIDPattern() {
     return '[1-9]\d*';
   }
@@ -104,7 +109,7 @@ abstract class PhabricatorRemarkupRuleObject
     // prefix does not start with a word character, we want to require no word
     // boundary for the same reasons. Test if the prefix starts with a word
     // character.
-    if (preg_match('/^\w/', $prefix)) {
+    if ($this->getObjectNamePrefixBeginsWithWordCharacter()) {
       $boundary = '\\b';
     } else {
       $boundary = '\\B';