src/libsyntax/ext/cfg.rs

   1 // Copyright 2013 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 /// The compiler code necessary to support the cfg! extension, which expands to
  12 /// a literal `true` or `false` based on whether the given cfg matches the
  13 /// current compilation environment.
  14
  15 use ast;
  16 use codemap::Span;
  17 use ext::base::*;
  18 use ext::base;
  19 use ext::build::AstBuilder;
  20 use attr;
  21 use attr::*;
  22 use parse::attr::ParserAttr;
  23 use parse::token;
  24
  25 pub fn expand_cfg<'cx>(cx: &mut ExtCtxt,
  26                        sp: Span,
  27                        tts: &[ast::TokenTree])
  28                        -> Box<base::MacResult+'static> {
  29     let mut p = cx.new_parser_from_tts(tts);
  30     let cfg = p.parse_meta_item();
  31
  32     if !panictry!(p.eat(&token::Eof)){
  33         cx.span_err(sp, "expected 1 cfg-pattern");
  34         return DummyResult::expr(sp);
  35     }
  36
  37     let matches_cfg = attr::cfg_matches(&cx.parse_sess.span_diagnostic, &cx.cfg, &*cfg,
  38                                         cx.feature_gated_cfgs);
  39     MacEager::expr(cx.expr_bool(sp, matches_cfg))
  40 }