From 95183ec529e176f033bc074fd4f137c9e203661d Mon Sep 17 00:00:00 2001
From: Deadbeef <ent3rm4n@gmail.com>
Date: Tue, 5 Apr 2022 20:33:06 +1000
Subject: [PATCH] Fix dead_code lint

---
 compiler/rustc_passes/src/dead.rs | 5 +++++
 library/core/src/clone.rs         | 1 +
 2 files changed, 6 insertions(+)

diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index c777074df4641..f000ff50362ac 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -268,6 +268,11 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                     }
                     return true;
                 }
+
+                // ignore generated `DerivedClone` but do not expose this to users.
+                if Some(trait_of) == self.tcx.get_diagnostic_item(sym::DerivedClone) {
+                    return true;
+                }
             }
         }
 
diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs
index af0c8aa2ee790..1c8c1f27a62dc 100644
--- a/library/core/src/clone.rs
+++ b/library/core/src/clone.rs
@@ -178,6 +178,7 @@ pub struct AssertParamIsCopy<T: Copy + ?Sized> {
     reason = "deriving hack, should not be public",
     issue = "none"
 )]
+#[rustc_diagnostic_item = "DerivedClone"]
 pub trait DerivedClone: Sized {
     fn clone(&self) -> Self;
 }