67 lines
2.0 KiB
Rust
67 lines
2.0 KiB
Rust
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![allow(unused_parens)]
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#![feature(plugin)]
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#![feature(plugin_registrar)]
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#![feature(rustc_private)]
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#![plugin(proc_macro)]
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extern crate rustc_plugin;
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extern crate proc_macro;
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extern crate syntax;
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use proc_macro::prelude::*;
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use rustc_plugin::Registry;
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use syntax::ast::Ident;
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use syntax::codemap::{DUMMY_SP, Span};
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use syntax::ext::proc_macro_shim::build_block_emitter;
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use syntax::ext::base::{ExtCtxt, MacResult};
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use syntax::parse::token::{self, Token, DelimToken, keywords, str_to_ident};
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use syntax::tokenstream::{TokenTree, TokenStream};
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#[plugin_registrar]
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pub fn plugin_registrar(reg: &mut Registry) {
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reg.register_macro("cond", cond);
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}
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fn cond<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResult + 'cx> {
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let output = cond_rec(TokenStream::from_tts(tts.clone().to_owned()));
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build_block_emitter(cx, sp, output)
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}
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fn cond_rec(input: TokenStream) -> TokenStream {
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if input.is_empty() {
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return qquote!();
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}
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let next = input.slice(0..1);
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let rest = input.slice_from(1..);
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let clause : TokenStream = match next.maybe_delimited() {
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Some(ts) => ts,
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_ => panic!("Invalid input"),
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};
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// clause is ([test]) [rhs]
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if clause.len() < 2 { panic!("Invalid macro usage in cond: {:?}", clause) }
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let test: TokenStream = clause.slice(0..1);
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let rhs: TokenStream = clause.slice_from(1..);
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if ident_eq(&test[0], str_to_ident("else")) || rest.is_empty() {
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qquote!({unquote(rhs)})
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} else {
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qquote!({if unquote(test) { unquote(rhs) } else { cond!(unquote(rest)) } })
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}
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}
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