errors: implement `IntoDiagnosticArg` for `&T`

Implement `IntoDiagnosticArg` for `&'a T` when `T` implements
`IntoDiagnosticArg` and `Clone`. Makes it easier to write diagnostic
structs that borrow something which implements `IntoDiagnosticArg`.

Signed-off-by: David Wood <david.wood@huawei.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index dad5e98aac0..d5a5ef3b445 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -36,6 +36,12 @@ impl<'a, T: fmt::Display> From<&'a T> for DiagnosticArgFromDisplay<'a> {
     }
 }
 
+impl<'a, T: Clone + IntoDiagnosticArg> IntoDiagnosticArg for &'a T {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        self.clone().into_diagnostic_arg()
+    }
+}
+
 macro_rules! into_diagnostic_arg_using_display {
     ($( $ty:ty ),+ $(,)?) => {
         $(