Heapless string for comrade qw1

Cargo.toml

[package]
name = "stack_string"
version = "0.1.0"
authors = ["Roman Proskuryakov <humbug@deeptown.org>"]
edition = "2018"

[dependencies]
libc = { version = "0.2", default-features = false }
heapless = { version = "0.4" }

[profile.release]
panic = "abort"

[profile.dev]
panic = "abort"

stack_string.rs

#![feature(lang_items, core_intrinsics)]
#![feature(start)]
#![no_std]
#![no_main]
use core::intrinsics;
use core::panic::PanicInfo;

// Pull in the system libc library for what crt0.o likely requires.
extern crate libc;

extern crate heapless;

use heapless::{String, Vec};
use heapless::consts::*;


#[no_mangle]
pub extern fn main() -> i32 {
    let mut users: Vec<UserInfo, U10> = Vec::new();
    for i in 0..10 {
        let user = UserInfo::new(i);
        users.push(user)
            .expect("Not enough space to push user");
    }
    register_users(&users);
    0
}

fn register_users(_users: &[UserInfo]) {}

#[derive(Debug)]
struct UserInfo {
    id: i32,
    name: String<U200>,
    pass: String<U200>,
}

impl UserInfo {
    pub fn new(id: i32) -> UserInfo {
        use core::fmt;

        let mut name = String::new();
        fmt::write(&mut name, format_args!("user{}", id))
            .expect("Not enough space to format user name");

        UserInfo {
            id,
            name,
            pass: String::from("***"),
        }
    }
}


// These functions are used by the compiler, but not
// for a bare-bones hello world. These are normally
// provided by libstd.
#[lang = "eh_personality"]
#[no_mangle]
pub extern fn rust_eh_personality() { }

// This function may be needed based on the compilation target.
#[lang = "eh_unwind_resume"]
#[no_mangle]
pub extern fn rust_eh_unwind_resume() { }

#[lang = "panic_impl"]
#[no_mangle]
pub extern fn rust_begin_panic(_info: &PanicInfo) -> ! {
    unsafe { intrinsics::abort() }
}