Code shared from the Rust Playground

playground.rs

// main.rs - A minimal Crust program with tests
//
#![cfg_attr(not(test), no_std)]
#![cfg_attr(not(test), no_main)]

extern crate libc;

#[cfg(not(test))]
use core::panic::PanicInfo;

#[cfg(not(test))]
//#[panic_handler]
#[allow(unused)]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

#[cfg(not(test))]
#[unsafe(no_mangle)]
pub extern "C" fn main() -> i32 {
    let s = b"Hello world!\n\0";
    unsafe {
        libc::printf(s.as_ptr() as *const i8);
    }
    0
}

#[allow(unused)]
fn add(x: u32, y: u32) -> u32 {
    let r = x + y;
    let s = "%d + %d = %d\n\0";
    unsafe {
        libc::printf(s.as_ptr() as *const i8, x, y, r);
    }
    r
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        let result = add(2, 2);
        assert_eq!(result, 4);
    }
}

#[allow(unused_imports)]
use anstream::println;

#[allow(unused)]
// build.rs - Required for building Crust programs (On Mac OS at least)
fn build_rs() {
    // Link against the system C library on macOS
    //println!("cargo:rustc-link-lib=System");
}
// Cargo.toml