Avoid warning in checking config classes in setup

Summary:
Current code emits warning for classes with constructors with parameters.
It also creates the objects which is bad if constructors do some actual work.

NOTE: http://svn.php.net/viewvc/phpdoc/en/trunk/reference/reflection/reflectionclass/issubclassof.xml?r1=324630&r2=324629

Test Plan:
Run setup with:

- correct classes
- not-existing class
- class with private constructor
- class not implementing the required class

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2056

src/infrastructure/setup/PhabricatorSetup.php

@@ -735,12 +735,19 @@ final class PhabricatorSetup {
     }
 
     self::writeHeader('CONFIG CLASSES');
-    foreach (PhabricatorEnv::getRequiredClasses() as $key => $class) {
-      if (!PhabricatorEnv::getEnvConfig($key)) {
+    foreach (PhabricatorEnv::getRequiredClasses() as $key => $instanceof) {
+      $config = PhabricatorEnv::getEnvConfig($key);
+      if (!$config) {
         self::writeNote("'$key' is not set.");
       } else {
         try {
-          PhabricatorEnv::newObjectFromConfig($key);
+          $r = new ReflectionClass($config);
+          if (!$r->isSubclassOf($instanceof)) {
+            throw new Exception(
+              "Config setting '$key' must be an instance of '$instanceof'.");
+          } elseif (!$r->isInstantiable()) {
+            throw new Exception("Config setting '$key' must be instantiable.");
+          }
         } catch (Exception $ex) {
           self::writeFailure();
           self::write("Setup failure! ".$ex->getMessage());