Remove `Clone` impl for `DiagnosticBuilder`.

It seems like a bad idea, just asking for diagnostics to be emitted
multiple times.

2 files changed, 5 insertions, 1 deletions

diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
index e018c14a4a5..fab5affbad1 100644
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -42,7 +42,6 @@ where
 /// access in the methods of `DiagnosticBuilder` here, consider
 /// extending `DiagCtxtFlags`.
 #[must_use]
-#[derive(Clone)]
 pub struct DiagnosticBuilder<'a, G: EmissionGuarantee = ErrorGuaranteed> {
     state: DiagnosticBuilderState<'a>,
 
@@ -55,6 +54,10 @@ pub struct DiagnosticBuilder<'a, G: EmissionGuarantee = ErrorGuaranteed> {
     _marker: PhantomData<G>,
 }
 
+// Cloning a `DiagnosticBuilder` is a recipe for a diagnostic being emitted
+// twice, which would be bad.
+impl<G> !Clone for DiagnosticBuilder<'_, G> {}
+
 #[derive(Clone)]
 enum DiagnosticBuilderState<'a> {
     /// Initial state of a `DiagnosticBuilder`, before `.emit()` or `.cancel()`.
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 25bec9f766b..e07a9509383 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -10,6 +10,7 @@
 #![feature(extract_if)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
+#![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![feature(yeet_expr)]