src/test/run-pass-fulldeps/auxiliary/cond_noprelude_plugin.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 #![allow(unused_parens)]
  12 #![feature(plugin)]
  13 #![feature(plugin_registrar)]
  14 #![feature(rustc_private)]
  15 #![plugin(proc_macro_plugin)]
  16
  17 extern crate rustc_plugin;
  18 extern crate proc_macro_tokens;
  19 extern crate syntax;
  20
  21 use proc_macro_tokens::build::ident_eq;
  22
  23 use syntax::ext::base::{ExtCtxt, MacResult};
  24 use syntax::ext::proc_macro_shim::build_block_emitter;
  25 use syntax::tokenstream::{TokenTree, TokenStream};
  26 use syntax::parse::token::str_to_ident;
  27 use syntax::codemap::Span;
  28
  29 use rustc_plugin::Registry;
  30
  31 #[plugin_registrar]
  32 pub fn plugin_registrar(reg: &mut Registry) {
  33     reg.register_macro("cond", cond);
  34 }
  35
  36 fn cond<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResult + 'cx> {
  37     let output = cond_rec(TokenStream::from_tts(tts.clone().to_owned()));
  38     build_block_emitter(cx, sp, output)
  39 }
  40
  41 fn cond_rec(input: TokenStream) -> TokenStream {
  42   if input.is_empty() {
  43       return qquote!();
  44   }
  45
  46   let next = input.slice(0..1);
  47   let rest = input.slice_from(1..);
  48
  49   let clause : TokenStream = match next.maybe_delimited() {
  50     Some(ts) => ts,
  51     _ => panic!("Invalid input"),
  52   };
  53
  54   // clause is ([test]) [rhs]
  55   if clause.len() < 2 { panic!("Invalid macro usage in cond: {:?}", clause) }
  56
  57   let test: TokenStream = clause.slice(0..1);
  58   let rhs: TokenStream = clause.slice_from(1..);
  59
  60   if ident_eq(&test[0], str_to_ident("else")) || rest.is_empty() {
  61     qquote!({unquote(rhs)})
  62   } else {
  63     qquote!({if unquote(test) { unquote(rhs) } else { cond!(unquote(rest)) } })
  64   }
  65 }