src/test/ui-fulldeps/auxiliary/roman-numerals.rs

// WARNING WARNING WARNING WARNING WARNING
// =======================================
//
// This code also appears in src/doc/unstable-book/src/language-features/plugin.md.
// Please keep the two copies in sync!  FIXME: have rustdoc read this file

// force-host

#![crate_type="dylib"]
#![feature(plugin_registrar, rustc_private)]

extern crate syntax;
extern crate syntax_pos;
extern crate rustc;
extern crate rustc_driver;

use syntax::parse::token::{self, Token};
use syntax::tokenstream::{TokenTree, TokenStream};
use syntax::ext::base::{ExtCtxt, MacResult, DummyResult, MacEager};
use syntax_pos::Span;
use rustc_driver::plugin::Registry;

fn expand_rn(cx: &mut ExtCtxt, sp: Span, args: TokenStream)
        -> Box<dyn MacResult + 'static> {

    static NUMERALS: &'static [(&'static str, usize)] = &[
        ("M", 1000), ("CM", 900), ("D", 500), ("CD", 400),
        ("C",  100), ("XC",  90), ("L",  50), ("XL",  40),
        ("X",   10), ("IX",   9), ("V",   5), ("IV",   4),
        ("I",    1)];

    if args.len() != 1 {
        cx.span_err(
            sp,
            &format!("argument should be a single identifier, but got {} arguments", args.len()));
        return DummyResult::any(sp);
    }

    let text = match args.into_trees().next().unwrap() {
        TokenTree::Token(Token { kind: token::Ident(s, _), .. }) => s.to_string(),
        _ => {
            cx.span_err(sp, "argument should be a single identifier");
            return DummyResult::any(sp);
        }
    };

    let mut text = &*text;
    let mut total = 0;
    while !text.is_empty() {
        match NUMERALS.iter().find(|&&(rn, _)| text.starts_with(rn)) {
            Some(&(rn, val)) => {
                total += val;
                text = &text[rn.len()..];
            }
            None => {
                cx.span_err(sp, "invalid Roman numeral");
                return DummyResult::any(sp);
            }
        }
    }

    MacEager::expr(cx.expr_usize(sp, total))
}

#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
    reg.register_macro("rn", expand_rn);
}