diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -274,6 +274,7 @@ pub struct Build {
 }
 
 #[derive(Debug)]
+#[allow (dead_code)]
 struct Crate {
     name: Interned<String>,
     deps: HashSet<Interned<String>>,