LanguageVersion parseLanguageVersion()

in lib/src/package_config_impl.dart [276:339]
56 lines of code
13 McCabe index (conditional complexity)

LanguageVersion parseLanguageVersion(
    String? source, void Function(Object error) onError) {
  var index = 0;
  // Reads a positive decimal numeral. Returns the value of the numeral,
  // or a negative number in case of an error.
  // Starts at [index] and increments the index to the position after
  // the numeral.
  // It is an error if the numeral value is greater than 0x7FFFFFFFF.
  // It is a recoverable error if the numeral starts with leading zeros.
  int readNumeral() {
    const maxValue = 0x7FFFFFFF;
    if (index == source!.length) {
      onError(PackageConfigFormatException('Missing number', source, index));
      return -1;
    }
    var start = index;

    var char = source.codeUnitAt(index);
    var digit = char ^ 0x30;
    if (digit > 9) {
      onError(PackageConfigFormatException('Missing number', source, index));
      return -1;
    }
    var firstDigit = digit;
    var value = 0;
    do {
      value = value * 10 + digit;
      if (value > maxValue) {
        onError(
            PackageConfigFormatException('Number too large', source, start));
        return -1;
      }
      index++;
      if (index == source.length) break;
      char = source.codeUnitAt(index);
      digit = char ^ 0x30;
    } while (digit <= 9);
    if (firstDigit == 0 && index > start + 1) {
      onError(PackageConfigFormatException(
          'Leading zero not allowed', source, start));
    }
    return value;
  }

  var major = readNumeral();
  if (major < 0) {
    return SimpleInvalidLanguageVersion(source);
  }
  if (index == source!.length || source.codeUnitAt(index) != $dot) {
    onError(PackageConfigFormatException("Missing '.'", source, index));
    return SimpleInvalidLanguageVersion(source);
  }
  index++;
  var minor = readNumeral();
  if (minor < 0) {
    return SimpleInvalidLanguageVersion(source);
  }
  if (index != source.length) {
    onError(PackageConfigFormatException(
        'Unexpected trailing character', source, index));
    return SimpleInvalidLanguageVersion(source);
  }
  return SimpleLanguageVersion(major, minor, source);
}