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

   1 // Copyright 2016 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)]
  16
  17 extern crate rustc_plugin;
  18 extern crate proc_macro;
  19 extern crate syntax;
  20
  21 use proc_macro::prelude::*;
  22
  23 use rustc_plugin::Registry;
  24
  25 use syntax::ast::Ident;
  26 use syntax::codemap::{DUMMY_SP, Span};
  27 use syntax::ext::proc_macro_shim::build_block_emitter;
  28 use syntax::ext::base::{ExtCtxt, MacResult};
  29 use syntax::parse::token::{self, Token, DelimToken, keywords, str_to_ident};
  30 use syntax::tokenstream::{TokenTree, TokenStream};
  31
  32 #[plugin_registrar]
  33 pub fn plugin_registrar(reg: &mut Registry) {
  34     reg.register_macro("cond", cond);
  35 }
  36
  37 fn cond<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResult + 'cx> {
  38     let output = cond_rec(TokenStream::from_tts(tts.clone().to_owned()));
  39     build_block_emitter(cx, sp, output)
  40 }
  41
  42 fn cond_rec(input: TokenStream) -> TokenStream {
  43   if input.is_empty() {
  44       return qquote!();
  45   }
  46
  47   let next = input.slice(0..1);
  48   let rest = input.slice_from(1..);
  49
  50   let clause : TokenStream = match next.maybe_delimited() {
  51     Some(ts) => ts,
  52     _ => panic!("Invalid input"),
  53   };
  54
  55   // clause is ([test]) [rhs]
  56   if clause.len() < 2 { panic!("Invalid macro usage in cond: {:?}", clause) }
  57
  58   let test: TokenStream = clause.slice(0..1);
  59   let rhs: TokenStream = clause.slice_from(1..);
  60
  61   if ident_eq(&test[0], str_to_ident("else")) || rest.is_empty() {
  62     qquote!({unquote(rhs)})
  63   } else {
  64     qquote!({if unquote(test) { unquote(rhs) } else { cond!(unquote(rest)) } })
  65   }
  66 }