1 files changed, 29 insertions, 0 deletions
diff --git a/compiler/rustc_builtin_macros/src/trace_macros.rs b/compiler/rustc_builtin_macros/src/trace_macros.rs
new file mode 100644
index 000000000..cc5ae6894
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/trace_macros.rs
@@ -0,0 +1,29 @@
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_expand::base::{self, ExtCtxt};
+use rustc_span::symbol::kw;
+use rustc_span::Span;
+
+pub fn expand_trace_macros(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    tt: TokenStream,
+) -> Box<dyn base::MacResult + 'static> {
+    let mut cursor = tt.into_trees();
+    let mut err = false;
+    let value = match &cursor.next() {
+        Some(TokenTree::Token(token, _)) if token.is_keyword(kw::True) => true,
+        Some(TokenTree::Token(token, _)) if token.is_keyword(kw::False) => false,
+        _ => {
+            err = true;
+            false
+        }
+    };
+    err |= cursor.next().is_some();
+    if err {
+        cx.span_err(sp, "trace_macros! accepts only `true` or `false`")
+    } else {
+        cx.set_trace_macros(value);
+    }
+
+    base::DummyResult::any_valid(sp)
+}