Windows Unicode conversion in Rust

hello-u8.rs

// Add to Cargo.toml
// [dependencies]
// winapi = "*"
// user32-sys = "*"
extern crate winapi;
extern crate user32;

fn from_wide_ptr(ptr: *const u16) -> String {
    use std::ffi::OsString;
    use std::os::windows::ffi::OsStringExt;
    unsafe {
        assert!(!ptr.is_null());
        let len = (0..std::isize::MAX).position(|i| *ptr.offset(i) == 0).unwrap();
        let slice = std::slice::from_raw_parts(ptr, len);
        OsString::from_wide(slice).to_string_lossy().into_owned()
    }
}

fn to_wide_chars(s: &str) -> Vec<u16> {
    use std::ffi::OsStr;
    use std::os::windows::ffi::OsStrExt;
    OsStr::new(s).encode_wide().chain(Some(0).into_iter()).collect::<Vec<_>>()
}

use std::fmt;
use std::ptr;

#[no_mangle]
pub extern "C" fn hello2(ptr: *const u16) {
    let y = from_wide_ptr(ptr);
    println!("X: {}", y);

    unsafe {
        user32::MessageBoxW(ptr::null_mut(),
                            to_wide_chars(&format!("こんにちは: {}", y)).as_ptr(),
                            to_wide_chars("世界").as_ptr(),
                            0);
    }
}