anchor.diff:  
   /// `true` if any file failed to compile.
   bool hadFailure = false;
  +
  +final _compilerPattern = new RegExp(r"import '(\.\./)+compiler");
   
   /// This runs the async/await compiler on all of the pub source code.
   ///
  
positive.code:     var sourceFile = entry as File;
      var destPath = p.join(buildDir, relative);
      var destFile = new File(destPath);
      if (!destFile.existsSync() ||
          entry.lastModifiedSync().isAfter(destFile.lastModifiedSync())) {
        _compile(sourceFile.path, sourceFile.readAsStringSync(), destPath);
        numCompiled++;
  
negative.code:   stderr.writeln("Usage: dart async_compile.dart <build dir> [--silent]");
    exit(64);
  }
  
  /// Deletes the file at [path], ignoring any IO errors that occur.
  ///
  /// This swallows errors to accommodate multiple compilers running concurrently.
  /// Since they will produce the same output anyway, a failure of one is fine.
  void _deleteFile(String path) {
    try {
      new File(path).deleteSync();
    } on IOException catch (ex) {
      // Do nothing.
    }
  }
  
  /// Writes [contents] to [path], ignoring any IO errors that occur.
  ///
  /// This swallows errors to accommodate multiple compilers running concurrently.
  /// Since they will produce the same output anyway, a failure of one is fine.
  void _writeFile(String path, String contents) {
    try {
      new File(path).writeAsStringSync(contents);
    } on IOException catch (ex) {
      // Do nothing.
    }
  }