Handling of escaped at-files is broken

[sormuras]

Handling of escaped at-files is broken:

• @@argfile should resolve to "@argfile", not "@@argfile", when seen in a pending argument
• Lines in an argument file starting with any number of @ characters should read as-is.

[sormuras]

Like this.

  static Stream<String> expandArgumentsFileToArguments(String arg) {
    if (!arg.startsWith("@")) return Stream.of(arg); // "abc" -> ["abc"]
    var substring = arg.substring(1); // "@...@abc" -> "...@abc"
    if (substring.startsWith("@")) return Stream.of(substring); // "@@abc" -> ["@abc"]
    var file = Path.of(substring);
    try {
      var expanded = new ArrayList<String>();
      for (var line : Files.readAllLines(file)) {
        line = line.strip();
        if (line.isEmpty()) continue; // skip empty line
        if (line.startsWith("#")) continue; // skip comment line
        expanded.add(line);
      }
      return expanded.stream();
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }

[sormuras]

The handling should be aligned to "spec by javac", as described here: https://docs.oracle.com/en/java/javase/19/docs/specs/man/javac.html#command-line-argument-files