From efad3ead528492f1ef9a63d6c582446d8d72f8a1 Mon Sep 17 00:00:00 2001
From: Amanieu d'Antras <amanieu@gmail.com>
Date: Mon, 24 Jan 2022 01:32:45 +0000
Subject: [PATCH] Fix std_detect_file_io

---
 library/stdarch/crates/std_detect/src/lib.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/library/stdarch/crates/std_detect/src/lib.rs b/library/stdarch/crates/std_detect/src/lib.rs
index bf9c707cb62d..c0e0de0dd5e6 100644
--- a/library/stdarch/crates/std_detect/src/lib.rs
+++ b/library/stdarch/crates/std_detect/src/lib.rs
@@ -24,6 +24,11 @@
 #[macro_use]
 extern crate std;
 
+// rust-lang/rust#83888: removing `extern crate` gives an error that `vec_spare>
+#[cfg_attr(feature = "std_detect_file_io", allow(unused_extern_crates))]
+#[cfg(feature = "std_detect_file_io")]
+extern crate alloc;
+
 #[doc(hidden)]
 #[unstable(feature = "stdsimd", issue = "27731")]
 pub mod detect;