Fix matching of very short project hashtags ending in a digit

Summary: Fixes T7625. The way the regexp worked, "unusual" terminal characters required at least one character as a prefix in order to match. Allow 0 instead, so `#a1` matches.

Test Plan: Added and executed unit test.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7625

Differential Revision: https://secure.phabricator.com/D12123

src/applications/project/remarkup/ProjectRemarkupRule.php

@@ -30,7 +30,7 @@ final class ProjectRemarkupRule extends PhabricatorObjectRemarkupRule {
     // In other contexts, the PhabricatorProjectProjectPHIDType pattern is
     // controlling and these names should parse correctly.
 
-    return '[^\s.\d!,:;{}#\(\)]+(?:[^\s!,:;{}#\(\)][^\s.!,:;{}#\(\)]+)*';
+    return '[^\s.\d!,:;{}#\(\)]+(?:[^\s!,:;{}#\(\)]*[^\s.!,:;{}#\(\)]+)*';
   }
 
   protected function loadObjects(array $ids) {

src/applications/project/remarkup/__tests__/ProjectRemarkupRuleTestCase.php

@@ -70,6 +70,17 @@ final class ProjectRemarkupRuleTestCase extends PhabricatorTestCase {
           ),
         ),
       ),
+
+      '#s3' => array(
+        'embed' => array(),
+        'ref' => array(
+          array(
+            'offset' => 1,
+            'id' => 's3',
+          ),
+        ),
+      ),
+
     );
 
     foreach ($cases as $input => $expect) {