Clean up an issue with meta-editing of edit engines

Summary:
Ref T9908. These meta-edit-engines are used to generate the main editengine UIs, but they're also editable.

Fix an exception when trying to edit the meta editengine.

Test Plan: Edited editengineconfiguration editengine.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9908

Differential Revision: https://secure.phabricator.com/D14783

src/applications/transactions/controller/PhabricatorEditEngineController.php

@@ -70,13 +70,6 @@ abstract class PhabricatorEditEngineController
       ->executeOne();
     if ($config) {
       $engine = $config->getEngine();
-
-      // TODO: When we're editing the meta-engine, we need to set the engine
-      // itself as its own target. This is hacky and it would be nice to find
-      // a cleaner approach later.
-      if ($engine instanceof PhabricatorEditEngineConfigurationEditEngine) {
-        $engine->setTargetEngine($engine);
-      }
     }
 
     return $config;

src/applications/transactions/editor/PhabricatorEditEngineConfigurationEditEngine.php

@@ -14,7 +14,8 @@ final class PhabricatorEditEngineConfigurationEditEngine
 
   public function getTargetEngine() {
     if (!$this->targetEngine) {
-      throw new PhutilInvalidStateException('setTargetEngine');
+      // If we don't have a target engine, assume we're editing ourselves.
+      return new PhabricatorEditEngineConfigurationEditEngine();
     }
     return $this->targetEngine;
   }