Remove the lifetime from `DiagnosticArgValue`.

Because it's almost always static.

This makes `impl IntoDiagnosticArg for DiagnosticArgValue` trivial,
which is nice.

There are a few diagnostics constructed in
`compiler/rustc_mir_build/src/check_unsafety.rs` and
`compiler/rustc_mir_transform/src/errors.rs` that now need symbols
converted to `String` with `to_string` instead of `&str` with `as_str`,
but that' no big deal, and worth it for the simplifications elsewhere.

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index 4ef3d47d6a6..30de40e226c 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -125,7 +125,7 @@ impl RequiresUnsafeDetail {
                 diag.arg(
                     "missing_target_features",
                     DiagnosticArgValue::StrListSepByAnd(
-                        missing.iter().map(|feature| Cow::from(feature.as_str())).collect(),
+                        missing.iter().map(|feature| Cow::from(feature.to_string())).collect(),
                     ),
                 );
                 diag.arg("missing_target_features_count", missing.len());
@@ -136,7 +136,7 @@ impl RequiresUnsafeDetail {
                         DiagnosticArgValue::StrListSepByAnd(
                             build_enabled
                                 .iter()
-                                .map(|feature| Cow::from(feature.as_str()))
+                                .map(|feature| Cow::from(feature.to_string()))
                                 .collect(),
                         ),
                     );