From 5d08a54141c180e2a6907f5e10c939864e0328a0 Mon Sep 17 00:00:00 2001
From: mu001999 <mu001999@outlook.com>
Date: Tue, 25 Jun 2024 23:29:44 +0800
Subject: [PATCH] Detect unused structs which derived Default

---
 alloc/src/sync/tests.rs | 2 +-
 core/src/default.rs     | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/alloc/src/sync/tests.rs b/alloc/src/sync/tests.rs
index 49eae718c1690..1b123aa58f205 100644
--- a/alloc/src/sync/tests.rs
+++ b/alloc/src/sync/tests.rs
@@ -396,7 +396,7 @@ fn show_arc() {
 
 // Make sure deriving works with Arc<T>
 #[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
-struct Foo {
+struct _Foo {
     inner: Arc<i32>,
 }
 
diff --git a/core/src/default.rs b/core/src/default.rs
index 4524b352ec817..5cacedcb241a5 100644
--- a/core/src/default.rs
+++ b/core/src/default.rs
@@ -103,6 +103,7 @@ use crate::ascii::Char as AsciiChar;
 /// ```
 #[cfg_attr(not(test), rustc_diagnostic_item = "Default")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(bootstrap), rustc_trivial_field_reads)]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///