Change old documentation that uses deprecated "do" syntax

[mijoharas]

in the rust documentation for 0.10 in the second block

use std::libc;
use std::ptr;

#[link(name = "readline")]
extern {
    static mut rl_prompt: *libc::c_char;
}

fn main() {
    do "[my-awesome-shell] $".as_c_str |buf| {
        unsafe { rl_prompt = buf; }
        // get a line, process it
        unsafe { rl_prompt = ptr::null(); }
    }
}

This will not compile as it uses the old do syntax that has been deprecated. Could we update it to the current syntax?

my attempt got it to compile but did not enable me to use readline (by trying to simply copy the code).

use std::libc;
use std::ptr;

#[link(name = "readline")]
extern {
    static mut rl_prompt: *libc::c_char;
}

fn main() {
        "[my-awesome-shell] $".with_c_str(|buf| {
                unsafe { rl_prompt = buf; }
                // get a line, process it
                unsafe { rl_prompt = ptr::null(); }
        })
}

Does anyone have a suggestion on how to make this work and whether there's a github repo for the documentation to send a PR to? (I couldn't find one.)

[sfackler]

That guide is in this repo right here: https://github.com/mozilla/rust/blob/master/src/doc/guide-ffi.md

[mijoharas]

ahhh, brilliant, thank you. Can anyone suggest the correct syntax for using readline with rust? (my attempted correction simply exits without doing anything, is this incorrect use of rust syntax or incorrect use of the readline library? (unfortunately I'm new to both.) original code is right here