Write bash builtin command in Rust

Cargo.toml

[package]
name = "hello_world"
version = "0.1.0"
authors = []

[lib]
name = "hello_world"
path = "./lib.rs"
crate-type = ["cdylib"]

lib.rs

#![allow(non_camel_case_types, non_upper_case_globals)]

use std::marker::Sync;
use std::os::raw::{c_char, c_int};

const EXECUTION_SUCCESS: c_int = 0;
const BUILTIN_ENABLED: c_int = 0x01;

#[repr(C)]
pub struct WORD_DESC {
  word: *mut c_char,
  dollar_present: c_int,
  quoted: c_int,
  assignment: c_int,
}

#[repr(C)]
pub struct WORD_LIST {
  next: *mut WORD_LIST,
  word: *mut WORD_DESC,
}

pub type sh_builtin_func_t = extern fn (*mut WORD_LIST) -> c_int;

#[repr(C)]
pub struct builtin {
  name: *mut c_char,
  function: sh_builtin_func_t,
  flags: c_int,
  long_doc: *mut *const c_char,
  short_doc: *mut c_char,
  handle: *mut c_char,
}

unsafe impl Sync for builtin {}

pub extern fn hello_world(_list: *mut WORD_LIST) -> c_int {
  println!("Hello, World!");
  EXECUTION_SUCCESS
}

const LONG_DOC: &'static [*const c_char] = &[
  b"Show a greeting message.\0" as *const _ as *const _,
  b"\0" as *const _ as *const _,
  b"It's far faster than launching executable file\0" as *const _ as *const _,
  b"because it't not necessary to call exec() and fork().\0" as *const _ as *const _,
  0 as *const _,
];

#[no_mangle]
pub static mut hello_world_struct: builtin = builtin {
  name: b"hello_world\0" as *const _ as *mut _,
  function: hello_world,
  flags: BUILTIN_ENABLED,
  long_doc: LONG_DOC as *const _ as *mut _,
  short_doc: b"hello_world\0" as *const _ as *mut _,
  handle: 0 as *mut _,
};