diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index e217c460..8cdcd2bb 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1,161 +1,162 @@
 <?php
 
 /**
  * This file is automatically generated. Use 'phutil_mapper.php' to rebuild it.
  * @generated
  */
 
 phutil_register_library_map(array(
   'class' =>
   array(
     'CommandException' => 'future/exec',
     'ConduitClient' => 'conduit/client',
     'ConduitClientException' => 'conduit/client',
     'ConduitFuture' => 'conduit/client',
     'ExecFuture' => 'future/exec',
     'FileFinder' => 'filesystem/filefinder',
     'FileList' => 'filesystem/filelist',
     'Filesystem' => 'filesystem',
     'FilesystemException' => 'filesystem',
     'Future' => 'future',
     'FutureIterator' => 'future',
     'FutureProxy' => 'future/proxy',
     'HTTPFuture' => 'future/http',
     'HTTPSFuture' => 'future/https',
     'LinesOfALargeFile' => 'filesystem/linesofalargefile',
     'MFilterTestHelper' => 'utils/__tests__',
     'PhutilConsoleFormatter' => 'console',
     'PhutilDaemon' => 'daemon/base',
     'PhutilDaemonOverseer' => 'daemon/overseer',
     'PhutilDefaultSyntaxHighlighterEngine' => 'markup/syntax/engine/default',
     'PhutilDocblockParser' => 'parser/docblock',
     'PhutilDocblockParserTestCase' => 'parser/docblock/__tests__',
     'PhutilErrorHandler' => 'error',
     'PhutilFatalDaemon' => 'daemon/torture/fatal',
     'PhutilHangForeverDaemon' => 'daemon/torture/hangforever',
     'PhutilInteractiveEditor' => 'console/editor',
     'PhutilMarkupEngine' => 'markup/engine',
     'PhutilMissingSymbolException' => 'symbols/exception/missing',
     'PhutilNiceDaemon' => 'daemon/torture/nice',
     'PhutilProcessGroupDaemon' => 'daemon/torture/processgroup',
     'PhutilReadableSerializer' => 'readableserializer',
     'PhutilRemarkupBlockStorage' => 'markup/engine/remarkup/blockstorage',
     'PhutilRemarkupEngine' => 'markup/engine/remarkup',
     'PhutilRemarkupEngineBlockRule' => 'markup/engine/remarkup/blockrule/base',
     'PhutilRemarkupEngineRemarkupCodeBlockRule' => 'markup/engine/remarkup/blockrule/remarkupcode',
     'PhutilRemarkupEngineRemarkupDefaultBlockRule' => 'markup/engine/remarkup/blockrule/remarkupdefault',
     'PhutilRemarkupEngineRemarkupHeaderBlockRule' => 'markup/engine/remarkup/blockrule/remarkupheader',
     'PhutilRemarkupEngineRemarkupInlineBlockRule' => 'markup/engine/remarkup/blockrule/remarkupinline',
     'PhutilRemarkupEngineRemarkupListBlockRule' => 'markup/engine/remarkup/blockrule/remarkuplist',
     'PhutilRemarkupEngineRemarkupQuotesBlockRule' => 'markup/engine/remarkup/blockrule/remarkupquotes',
     'PhutilRemarkupEngineTestCase' => 'markup/engine/remarkup/__tests__',
     'PhutilRemarkupRule' => 'markup/engine/remarkup/markuprule/base',
     'PhutilRemarkupRuleBold' => 'markup/engine/remarkup/markuprule/bold',
     'PhutilRemarkupRuleEscapeHTML' => 'markup/engine/remarkup/markuprule/escapehtml',
     'PhutilRemarkupRuleEscapeRemarkup' => 'markup/engine/remarkup/markuprule/escaperemarkup',
     'PhutilRemarkupRuleHyperlink' => 'markup/engine/remarkup/markuprule/hyperlink',
     'PhutilRemarkupRuleItalic' => 'markup/engine/remarkup/markuprule/italics',
     'PhutilRemarkupRuleLinebreaks' => 'markup/engine/remarkup/markuprule/linebreaks',
     'PhutilRemarkupRuleMonospace' => 'markup/engine/remarkup/markuprule/monospace',
     'PhutilSaturateStdoutDaemon' => 'daemon/torture/saturatestdout',
     'PhutilSymbolLoader' => 'symbols',
     'PhutilSyntaxHighlighter' => 'markup/syntax/highlighter/base',
     'PhutilSyntaxHighlighterEngine' => 'markup/syntax/engine/base',
     'PhutilTortureTestDaemon' => 'daemon/torture/base',
     'PhutilURI' => 'parser/uri',
     'PhutilUtilsTestCase' => 'utils/__tests__',
     'PhutilXHPASTSyntaxHighlighter' => 'markup/syntax/highlighter/xhpast',
     'TempFile' => 'filesystem/tempfile',
     'XHPASTNode' => 'parser/xhpast/api/node',
     'XHPASTNodeList' => 'parser/xhpast/api/list',
     'XHPASTSyntaxErrorException' => 'parser/xhpast/api/exception',
     'XHPASTToken' => 'parser/xhpast/api/token',
     'XHPASTTree' => 'parser/xhpast/api/tree',
     'XHPASTTreeTestCase' => 'parser/xhpast/api/tree/__tests__',
   ),
   'function' =>
   array(
     'Futures' => 'future',
     'array_select_keys' => 'utils',
     'coalesce' => 'utils',
     'csprintf' => 'xsprintf/csprintf',
     'exec_manual' => 'future/exec',
     'execx' => 'future/exec',
     'head' => 'utils',
     'id' => 'utils',
     'idx' => 'utils',
     'ifilter' => 'utils',
     'igroup' => 'utils',
     'ipull' => 'utils',
     'isort' => 'utils',
     'jsprintf' => 'xsprintf/jsprintf',
     'mfilter' => 'utils',
     'mgroup' => 'utils',
     'mpull' => 'utils',
     'msort' => 'utils',
     'newv' => 'utils',
     'nonempty' => 'utils',
     'phlog' => 'error',
     'phutil_autoload_class' => 'autoload',
     'phutil_console_confirm' => 'console',
     'phutil_console_format' => 'console',
     'phutil_console_prompt' => 'console',
     'phutil_console_wrap' => 'console',
+    'phutil_error_listener_example' => 'error',
     'phutil_escape_html' => 'markup',
     'phutil_escape_uri' => 'markup',
     'phutil_get_library_name_for_root' => 'moduleutils',
     'phutil_get_library_root' => 'moduleutils',
     'phutil_get_library_root_for_path' => 'moduleutils',
     'phutil_is_utf8' => 'utils',
     'phutil_render_tag' => 'markup',
     'phutil_utf8ize' => 'utils',
     'vcsprintf' => 'xsprintf/csprintf',
     'vjsprintf' => 'xsprintf/jsprintf',
     'xhp_parser_node_constants' => 'parser/xhpast/constants',
     'xhpast_get_binary_path' => 'parser/xhpast/bin',
     'xhpast_get_build_instructions' => 'parser/xhpast/bin',
     'xhpast_get_parser_future' => 'parser/xhpast/bin',
     'xhpast_is_available' => 'parser/xhpast/bin',
     'xhpast_parser_token_constants' => 'parser/xhpast/constants',
     'xsprintf' => 'xsprintf',
     'xsprintf_callback_example' => 'xsprintf',
     'xsprintf_command' => 'xsprintf/csprintf',
     'xsprintf_javascript' => 'xsprintf/jsprintf',
   ),
   'requires_class' =>
   array(
     'ConduitFuture' => 'FutureProxy',
     'ExecFuture' => 'Future',
     'FutureProxy' => 'Future',
     'HTTPFuture' => 'Future',
     'HTTPSFuture' => 'Future',
     'PhutilDefaultSyntaxHighlighterEngine' => 'PhutilSyntaxHighlighterEngine',
     'PhutilDocblockParserTestCase' => 'ArcanistPhutilTestCase',
     'PhutilFatalDaemon' => 'PhutilTortureTestDaemon',
     'PhutilHangForeverDaemon' => 'PhutilTortureTestDaemon',
     'PhutilNiceDaemon' => 'PhutilTortureTestDaemon',
     'PhutilProcessGroupDaemon' => 'PhutilTortureTestDaemon',
     'PhutilRemarkupEngine' => 'PhutilMarkupEngine',
     'PhutilRemarkupEngineRemarkupCodeBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupDefaultBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupHeaderBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupInlineBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupListBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineRemarkupQuotesBlockRule' => 'PhutilRemarkupEngineBlockRule',
     'PhutilRemarkupEngineTestCase' => 'ArcanistPhutilTestCase',
     'PhutilRemarkupRuleBold' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleEscapeHTML' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleEscapeRemarkup' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleHyperlink' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleItalic' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleLinebreaks' => 'PhutilRemarkupRule',
     'PhutilRemarkupRuleMonospace' => 'PhutilRemarkupRule',
     'PhutilSaturateStdoutDaemon' => 'PhutilTortureTestDaemon',
     'PhutilTortureTestDaemon' => 'PhutilDaemon',
     'PhutilUtilsTestCase' => 'ArcanistPhutilTestCase',
     'XHPASTTreeTestCase' => 'ArcanistPhutilTestCase',
   ),
   'requires_interface' =>
   array(
   ),
 ));
diff --git a/src/filesystem/filefinder/FileFinder.php b/src/filesystem/filefinder/FileFinder.php
index 2144103a..80c0d9d4 100644
--- a/src/filesystem/filefinder/FileFinder.php
+++ b/src/filesystem/filefinder/FileFinder.php
@@ -1,206 +1,206 @@
 <?php
 
 /*
  * Copyright 2011 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *   http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 /**
  * Find files on disk matching criteria, like the 'find' system utility. Use of
  * this class is straightforward:
  *
  *    // Find PHP files in /tmp
  *    $files = id(new FileFinder('/tmp'))
  *      ->withType('f')
  *      ->withSuffix('php')
  *      ->find();
  *
  * @task  create    Creating a File Query
  * @task  config    Configuring File Queries
  * @task  exec      Executing the File Query
  * @task  internal  Internal
  * @group filesystem
  */
 final class FileFinder {
 
   private $root;
   private $exclude = array();
   private $paths = array();
   private $suffix = array();
   private $type;
   private $generateChecksums = false;
   private $followSymlinks;
 
   /**
    * Create a new FileFinder.
    *
    * @param string Root directory to find files beneath.
    * @return this
    * @task create
    */
   public function __construct($root) {
     $this->root = $root;
   }
 
   /**
    * @task config
    */
   public function excludePath($path) {
     $this->exclude[] = $path;
     return $this;
   }
 
   /**
    * @task config
    */
   public function withSuffix($suffix) {
     $this->suffix[] = '*.'.$suffix;
     return $this;
   }
 
   /**
    * @task config
    */
   public function withPath($path) {
     $this->paths[] = $path;
     return $this;
   }
 
   /**
    * @task config
    */
   public function withType($type) {
     $this->type = $type;
     return $this;
   }
 
   /**
    * @task config
    */
   public function withFollowSymlinks($follow) {
     $this->followSymlinks = $follow;
     return $this;
   }
 
   /**
    * @task config
    */
   public function setGenerateChecksums($generate) {
     $this->generateChecksums = $generate;
     return $this;
   }
 
   /**
    * @task exec
    */
   public function find() {
     $args = array();
     $command = array();
 
     $command[] = '(cd %s; ';
     $args[] = $this->root;
 
     $command[] = 'find';
     if ($this->followSymlinks) {
       $command[] = '-L';
     }
     $command[] = '.';
 
     if ($this->exclude) {
       $command[] = $this->generateList('path', $this->exclude).' -prune';
       $command[] = '-o';
     }
 
     if ($this->type) {
       $command[] = '-type %s';
       $args[] = $this->type;
     }
 
     if ($this->suffix) {
       $command[] = $this->generateList('name', $this->suffix);
     }
 
     if ($this->paths) {
       $command[] = $this->generateList('wholename', $this->paths);
     }
 
     $command[] = '-print0';
 
     if ($this->generateChecksums) {
       static $md5sum_binary = null;
       if ($md5sum_binary == null) {
 
         $options = array(
           'md5sum' => 'md5sum',
           'md5'    => 'md5 -r',
         );
         foreach ($options as $bin => $choose) {
           list($err) = exec_manual('which %s', $bin);
           if ($err == 0) {
             $md5sum_binary = $choose;
             break;
           }
         }
         if ($md5sum_binary === null) {
           throw new Exception(
             "Unable to locate the md5/md5sum binary for this system.");
         }
       }
       $command[] = ' | xargs -0 -n512 '.$md5sum_binary;
     }
 
     $command[] = ')';
 
     list($stdout) = call_user_func_array(
       'execx',
       array_merge(
         array(implode(' ', $command)),
         $args));
 
+    $stdout = trim($stdout);
+    if (!strlen($stdout)) {
+      return array();
+    }
+
     if (!$this->generateChecksums) {
-      return explode("\0", trim($stdout));
+      return explode("\0", $stdout);
     } else {
-      $stdout = trim($stdout);
-      if (!strlen($stdout)) {
-        return array();
-      }
-
       $map = array();
       foreach (explode("\n", $stdout) as $line) {
         $file = substr($line, 34);
         if ($file == '-') {
           continue;
         }
         // This mess is to make this class work on both mainline Linux systems
         // and OSX, which has subtly different 'find' semantics.
         $file = $this->root.ltrim($file, '.');
         $map[$file] = substr($line, 0, 32);
       }
       return $map;
     }
   }
 
   /**
    * @task internal
    */
   private function generateList($flag, array $items) {
     $items = array_map('escapeshellarg', $items);
     foreach ($items as $key => $item) {
       $items[$key] = '-'.$flag.' '.$item;
     }
     $items = implode(' -o ', $items);
     return '\\( '.$items.' \\)';
   }
 }