anchor.diff:      var imports = <Import>[];
       do {
         whitespace();
  -      imports.add(_importArgument());
  +      imports.add(_importArgument(start));
         whitespace();
       } while (scanner.scanChar($comma));
       expectStatementSeparator();
  
positive.code:       return new StaticImport(interpolation, scanner.spanFrom(start),
            supports: queries?.item1, media: queries?.item2);
      } else if (_inControlDirective || _inMixin) {
        _disallowedAtRule(start);
        return null;
      } else {
        try {
  
negative.code:     return new ImportRule(imports, scanner.spanFrom(start));
    }
  
    /// Consumes an argument to an `@import` rule.
    ///
    /// [ruleStart] should point before the `@`.
    Import _importArgument(LineScannerState ruleStart) {
      var start = scanner.state;
      var next = scanner.peekChar();
      if (next == $u || next == $U) {
  