From 7b72cc6156261e1a7243c9171bb48ccc7b54020d Mon Sep 17 00:00:00 2001
From: joboet <jonasboettiger@icloud.com>
Date: Tue, 11 Feb 2025 11:42:22 +0100
Subject: [PATCH] make `TrivialClone` a `#[marker]`-trait to keep it from
 appearing in error messages

---
 library/core/src/clone.rs                            |  4 ++++
 .../duplicate-derive-copy-clone-diagnostics.rs       |  1 -
 .../duplicate-derive-copy-clone-diagnostics.stderr   | 12 +-----------
 3 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs
index 4f76abdb7751..eeb26043b39b 100644
--- a/library/core/src/clone.rs
+++ b/library/core/src/clone.rs
@@ -275,6 +275,10 @@ fn clone_from(&mut self, source: &Self)
 // its invariant holds whenever `Clone` is implemented, even if the actual
 // `TrivialClone` bound would not be satisfied because of lifetime bounds.
 #[rustc_unsafe_specialization_marker]
+// If `#[derive(Clone, Clone, Copy)]` is written, there will be multiple
+// implementations of `TrivialClone`. To keep it from appearing in error
+// messages, make it a `#[marker]` trait.
+#[marker]
 pub const unsafe trait TrivialClone: [const] Clone {}
 
 /// Derive macro generating an impl of the trait `Clone`.
diff --git a/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.rs b/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.rs
index bc88a0e131a8..c4fb620fea4f 100644
--- a/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.rs
+++ b/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.rs
@@ -6,7 +6,6 @@
 #[derive(Copy, Clone)]
 //~^ ERROR conflicting implementations of trait `Clone` for type `E`
 //~| ERROR conflicting implementations of trait `Copy` for type `E`
-//~| ERROR conflicting implementations of trait `TrivialClone` for type `E`
 enum E {}
 
 fn main() {}
diff --git a/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.stderr b/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.stderr
index a0274222e78c..b9eb6194f6c4 100644
--- a/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.stderr
+++ b/tests/ui/derives/duplicate-derive-copy-clone-diagnostics.stderr
@@ -6,16 +6,6 @@ LL | #[derive(Copy, Clone)]
 LL | #[derive(Copy, Clone)]
    |          ^^^^ conflicting implementation for `E`
 
-error[E0119]: conflicting implementations of trait `TrivialClone` for type `E`
-  --> $DIR/duplicate-derive-copy-clone-diagnostics.rs:6:16
-   |
-LL | #[derive(Copy, Clone)]
-   |                ----- first implementation here
-LL | #[derive(Copy, Clone)]
-   |                ^^^^^ conflicting implementation for `E`
-   |
-   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0119]: conflicting implementations of trait `Clone` for type `E`
   --> $DIR/duplicate-derive-copy-clone-diagnostics.rs:6:16
    |
@@ -24,6 +14,6 @@ LL | #[derive(Copy, Clone)]
 LL | #[derive(Copy, Clone)]
    |                ^^^^^ conflicting implementation for `E`
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0119`.