src/libsyntax_ext/trace_macros.rs

   1 use syntax::ext::base::{self, ExtCtxt};
   2 use syntax::feature_gate;
   3 use syntax::symbol::{kw, sym};
   4 use syntax_pos::Span;
   5 use syntax::tokenstream::TokenTree;
   6
   7 pub fn expand_trace_macros(cx: &mut ExtCtxt<'_>,
   8                            sp: Span,
   9                            tt: &[TokenTree])
  10                            -> Box<dyn base::MacResult + 'static> {
  11     if !cx.ecfg.enable_trace_macros() {
  12         feature_gate::emit_feature_err(&cx.parse_sess,
  13                                        sym::trace_macros,
  14                                        sp,
  15                                        feature_gate::GateIssue::Language,
  16                                        feature_gate::EXPLAIN_TRACE_MACROS);
  17     }
  18
  19     match (tt.len(), tt.first()) {
  20         (1, Some(&TokenTree::Token(_, ref tok))) if tok.is_keyword(kw::True) => {
  21             cx.set_trace_macros(true);
  22         }
  23         (1, Some(&TokenTree::Token(_, ref tok))) if tok.is_keyword(kw::False) => {
  24             cx.set_trace_macros(false);
  25         }
  26         _ => cx.span_err(sp, "trace_macros! accepts only `true` or `false`"),
  27     }
  28
  29     base::DummyResult::any_valid(sp)
  30 }