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_plugin)]
  16
  17 extern crate rustc_plugin;
  18 extern crate syntax;
  19
  20 use rustc_plugin::Registry;
  21
  22 use syntax::ext::base::SyntaxExtension;
  23 use syntax::parse::token::Token;
  24 use syntax::symbol::Symbol;
  25 use syntax::tokenstream::{TokenTree, TokenStream};
  26
  27 #[plugin_registrar]
  28 pub fn plugin_registrar(reg: &mut Registry) {
  29     reg.register_syntax_extension(Symbol::intern("cond"),
  30                                   SyntaxExtension::ProcMacro(Box::new(cond)));
  31 }
  32
  33 fn cond(input: TokenStream) -> TokenStream {
  34     let mut conds = Vec::new();
  35     let mut input = input.trees();
  36     while let Some(tree) = input.next() {
  37         let cond: TokenStream = match *tree {
  38             TokenTree::Delimited(_, ref delimited) => delimited.tts.iter().cloned().collect(),
  39             _ => panic!("Invalid input"),
  40         };
  41         let mut trees = cond.trees().cloned();
  42         let test = trees.next();
  43         let rhs = trees.collect::<TokenStream>();
  44         if rhs.is_empty() {
  45             panic!("Invalid macro usage in cond: {}", cond);
  46         }
  47         let is_else = match test {
  48             Some(TokenTree::Token(_, Token::Ident(ident))) if ident.name == "else" => true,
  49             _ => false,
  50         };
  51         conds.push(if is_else || input.peek().is_none() {
  52             qquote!({ unquote rhs })
  53         } else {
  54             qquote!(if unquote(test.unwrap()) { unquote rhs } else)
  55         });
  56     }
  57
  58     conds.into_iter().collect()
  59 }