proc permits upvars to be moved repeatedly in a loop

[nickdesaulniers]

use std::io::net::ip::{SocketAddr, Ipv4Addr};
use std::io::net::tcp::{TcpListener, TcpAcceptor, TcpStream};
use std::io::stdio::println;
use std::io::{Listener, Acceptor};

fn main () {
  let addr: SocketAddr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 3000 };
  let listener: TcpListener = match TcpListener::bind(addr) {
    Err(e) => { println(e.desc); return; },
    Ok(l) => l
  };

  let acceptor: TcpAcceptor = match listener.listen() {
    Err(e) => { println(e.desc); return; },
    Ok(a) => a
  };

  let (port, chan): (Port<TcpStream>, Chan<TcpStream>) = Chan::new();
  spawn(proc() {
    loop {
      let mut acceptor = acceptor;
      let stream: TcpStream = match acceptor.accept() {
        Err(e) => { println(e.desc); return; },
        Ok(s) => s
      };
      chan.send(stream);
    }
  });
  spawn(proc() {
    let mut stream: TcpStream = port.recv();
    match stream.read_to_str() {
      Err(e) => { println(e.desc); return; },
      Ok(msg) => println(msg)
    }
  });
}

compiles rustc chat.rs. Runs ./chat. telnet localhost 3000 Connection refused and segfault.

[alexcrichton]

This is a bug in the treatment of captured variables. The line in question is:

loop {
    let mut acceptor = acceptor;
}

This is moving into the loop repeatedly when you should only be allowed to do it once. I think I've seen this bug before, but just in case, cc @nikomatsakis

[nikomatsakis]

thanks @alexcrichton, I've seen some reports of bugs like this before -- it's clear that we need to revisit the code used to check "once fns" -- it was added as a temporary start towards support (under a -Z flag) and then pressed into full service, clearly not quite ready for prime time.

[alexcrichton]

Nominating.

[nikomatsakis]

updated title to reflect the real issue at hand.

[flaper87]

cc @flaper87

[pnkfelix]

Assigning 1.0, max(P-backcompat-lang, P-high). Gotta fix.

edit: The use of max above is sort of a joke: take the max of the two P-tag inputs. (Also, I originally wrote P-backcompat-libs, but I'm pretty sure that was a typo.)