Implement IntoDiagArg for RustcVersion

compiler/rustc_session/src/version.rs

@@ -1,5 +1,10 @@
 use rustc_macros::{current_rustc_version, Decodable, Encodable, HashStable_Generic};
-use std::fmt::{self, Display};
+use std::{
+    borrow::Cow,
+    fmt::{self, Display},
+};
+
+use rustc_errors::IntoDiagArg;
 
 #[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[derive(HashStable_Generic)]
@@ -18,3 +23,9 @@ fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(formatter, "{}.{}.{}", self.major, self.minor, self.patch)
     }
 }
+
+impl IntoDiagArg for RustcVersion {
+    fn into_diag_arg(self) -> rustc_errors::DiagArgValue {
+        rustc_errors::DiagArgValue::Str(Cow::Owned(self.to_string()))
+    }
+}