Project - add editor-level support for detecting name conflicts

Summary: Fixes T4833. I wish there was an elegant way to catch this exception but I think the stack is written such that we really should just do this one-off query here...

Test Plan: from the "create project" link under "edit task" I received a more detailed exception than the report in T4833 post patch. I also tested editing an existing project - yay - and editing an existing project to some other existing project's name - got a nice error dialogue.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4833

Differential Revision: https://secure.phabricator.com/D8834

src/applications/project/editor/PhabricatorProjectTransactionEditor.php

@@ -179,6 +179,25 @@ final class PhabricatorProjectTransactionEditor
           $error->setIsMissingFieldError(true);
           $errors[] = $error;
         }
+
+        if (!$xactions) {
+          break;
+        }
+
+        $name = last($xactions)->getNewValue();
+        $name_used_already = id(new PhabricatorProjectQuery())
+          ->setViewer($this->getActor())
+          ->withNames(array($name))
+          ->executeOne();
+        if ($name_used_already &&
+           ($name_used_already->getPHID() != $object->getPHID())) {
+          $error = new PhabricatorApplicationTransactionValidationError(
+            $type,
+            pht(''),
+            pht('Project name is already used.'),
+            nonempty(last($xactions), null));
+          $errors[] = $error;
+        }
         break;
     }