diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index 765a21fd93e..6e47ff7d740 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -4,7 +4,10 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/", test(attr(deny(warnings))))]
+#![doc(
+    html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
+    test(attr(deny(warnings)))
+)]
 #![feature(box_syntax)]
 #![feature(const_fn)] // For the `transmute` in `P::new`
 #![feature(const_fn_transmute)]