Code to reproduce weird `String.cstring()` behaviour in ponyc

scratch.pony

use "net"
use "cli"
use "debug"

actor Main
  new create(env: Env) =>
    try
      let spec = CommandSpec.leaf("damn", "", [
        OptionSpec.string("addr",
          "The host:port:name to be advertised to other clustering nodes."
          where short' = 'a', default' = "127.0.0.1:9999:")
      ], [
        ArgSpec.string_seq("", "")
      ])?.>add_help()?

      let cmd =
        match CommandParser(spec).parse(env.args, env.vars())
        | let c: Command => c
        | let c: CommandHelp =>
          c.print_help(env.out)
          env.exitcode(0)
          error
        | let err: SyntaxError =>
          env.out.print(err.string())
          env.exitcode(1)
          error
        end

      let s = cmd.option("addr").string()
      let i1 = s.find(":")?
      let i2 = s.find(":", (i1 + 1).isize())?
      let s2 = s.trim(i1.usize() + 1, i2.usize())

      TCPListener(
        env.root as AmbientAuth,
        object iso is TCPListenNotify
         fun ref listening(listen: TCPListener ref) =>
           env.out.write(".")
           listen.close()
         fun ref not_listening(listen: TCPListener ref) =>
           env.out.write("E")
         fun ref connected(listen: TCPListener ref): TCPConnectionNotify iso^ ? =>
           error
       end,
       "",
       s2)
    end