compiler/rustc_builtin_macros/src/cfg.rs

   1 //! The compiler code necessary to support the cfg! extension, which expands to
   2 //! a literal `true` or `false` based on whether the given cfg matches the
   3 //! current compilation environment.
   4
   5 use rustc_ast as ast;
   6 use rustc_ast::token;
   7 use rustc_ast::tokenstream::TokenStream;
   8 use rustc_attr as attr;
   9 use rustc_errors::PResult;
  10 use rustc_expand::base::{self, *};
  11 use rustc_macros::Diagnostic;
  12 use rustc_span::Span;
  13
  14 pub fn expand_cfg(
  15     cx: &mut ExtCtxt<'_>,
  16     sp: Span,
  17     tts: TokenStream,
  18 ) -> Box<dyn base::MacResult + 'static> {
  19     let sp = cx.with_def_site_ctxt(sp);
  20
  21     match parse_cfg(cx, sp, tts) {
  22         Ok(cfg) => {
  23             let matches_cfg = attr::cfg_matches(
  24                 &cfg,
  25                 &cx.sess.parse_sess,
  26                 cx.current_expansion.lint_node_id,
  27                 cx.ecfg.features,
  28             );
  29             MacEager::expr(cx.expr_bool(sp, matches_cfg))
  30         }
  31         Err(mut err) => {
  32             err.emit();
  33             DummyResult::any(sp)
  34         }
  35     }
  36 }
  37
  38 #[derive(Diagnostic)]
  39 #[diag(builtin_macros_requires_cfg_pattern)]
  40 struct RequiresCfgPattern {
  41     #[primary_span]
  42     #[label]
  43     span: Span,
  44 }
  45
  46 #[derive(Diagnostic)]
  47 #[diag(builtin_macros_expected_one_cfg_pattern)]
  48 struct OneCfgPattern {
  49     #[primary_span]
  50     span: Span,
  51 }
  52
  53 fn parse_cfg<'a>(cx: &mut ExtCtxt<'a>, span: Span, tts: TokenStream) -> PResult<'a, ast::MetaItem> {
  54     let mut p = cx.new_parser_from_tts(tts);
  55
  56     if p.token == token::Eof {
  57         return Err(cx.create_err(RequiresCfgPattern { span }));
  58     }
  59
  60     let cfg = p.parse_meta_item()?;
  61
  62     let _ = p.eat(&token::Comma);
  63
  64     if !p.eat(&token::Eof) {
  65         return Err(cx.create_err(OneCfgPattern { span }));
  66     }
  67
  68     Ok(cfg)
  69 }