>>>
var paths = new Directory(inputDir).listSync()
     .where((f) => f is File).map((f) => f.path)
     .where((p) => p.endsWith('.dart') && filePattern.hasMatch(p));
<<<
var paths = new Directory(inputDir)
    .listSync()
    .where((f) => f is File)
    .map((f) => f.path)
    .where((p) => p.endsWith('.dart') && filePattern.hasMatch(p));