Check that Phurl alias is unique

Summary: Ref T8992, Phurl aliases must be unique. Otherwise throw an error.

Test Plan: Create two Phurl's both with alias 'asdf'. When saving second Phurl, form should show an error about the duplicate alias.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T8992

Differential Revision: https://secure.phabricator.com/D14401

src/applications/phurl/editor/PhabricatorPhurlURLEditor.php

@@ -248,5 +248,19 @@ final class PhabricatorPhurlURLEditor
     return $body;
   }
 
+  protected function didCatchDuplicateKeyException(
+    PhabricatorLiskDAO $object,
+    array $xactions,
+    Exception $ex) {
+
+    $errors = array();
+    $errors[] = new PhabricatorApplicationTransactionValidationError(
+      PhabricatorPhurlURLTransaction::TYPE_ALIAS,
+      pht('Duplicate'),
+      pht('This alias is already in use.'),
+      null);
+
+    throw new PhabricatorApplicationTransactionValidationException($errors);
+  }
 
 }