session: impl IntoDiagnosticArg for CrateType

Forward the `Display` implementation for `CrateType` to
`IntoDiagnosticArg` so that it can be used in diagnostic structs.

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

Author: davidtwco

compiler/rustc_session/src/config.rs

@@ -25,7 +25,7 @@ use rustc_span::RealFileName;
 use rustc_span::SourceFileHashAlgorithm;
 
 use rustc_errors::emitter::HumanReadableErrorType;
-use rustc_errors::{ColorConfig, HandlerFlags};
+use rustc_errors::{ColorConfig, DiagnosticArgValue, HandlerFlags, IntoDiagnosticArg};
 
 use std::collections::btree_map::{
     Iter as BTreeMapIter, Keys as BTreeMapKeysIter, Values as BTreeMapValuesIter,
@@ -2638,6 +2638,12 @@ impl fmt::Display for CrateType {
     }
 }
 
+impl IntoDiagnosticArg for CrateType {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        self.to_string().into_diagnostic_arg()
+    }
+}
+
 #[derive(Copy, Clone, PartialEq, Debug)]
 pub enum PpSourceMode {
     /// `-Zunpretty=normal`