anchor.diff:    throw new StateError("No such position in file: line $line, column $column");
   }
   
  +String _resolveEnvVars(String s) =>
  +    s.replaceAllMapped(
  +        new RegExp(r'\$\{([^}]+)\}'),
  +        (Match m) => (Platform.environment[m.group(1)] ?? ''));
  +
   // _normalize(String path) {
   //   while (true) {
   //     var newPath = path.replaceAll(new RegExp(r'\.\./\.?[^./]+/|(^|/)\./'), '');
  
positive.code:      String sasscPath: 'sassc',
       List<String> sasscArgs: const<String>[]}) async {
  
    var sassId = sassAsset.id;
    var sassContent = sassAsset.readAsString();
    var dir = await Directory.systemTemp.createTemp();
  
negative.code: 
  final _multilineRx = new RegExp(r'^.*?$', multiLine: true);
  
  SourceLocation _computeSourceSpan(String content, String sourceUrl, int line, int column) {
    int nextLine = 1;
    for (var match in _multilineRx.allMatches(content)) {
      if (line == nextLine) {
  