avoid unnecessary &str to String conversions

Author: TaKO8Ki

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -507,7 +507,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
                                 _ => "aren't",
                             },
                         ),
-                        " else { todo!() }".to_string(),
+                        " else { todo!() }",
                         Applicability::HasPlaceholders,
                     );
                 }

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -784,10 +784,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
             return false;
         }
         err.code(rustc_errors::error_code!(E0411));
-        err.span_label(
-            span,
-            "`Self` is only available in impls, traits, and type definitions".to_string(),
-        );
+        err.span_label(span, "`Self` is only available in impls, traits, and type definitions");
         if let Some(item_kind) = self.diagnostic_metadata.current_item {
             err.span_label(
                 item_kind.ident.span,

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -192,12 +192,12 @@ pub fn is_const_evaluatable<'tcx>(
         }
         let concrete = infcx.const_eval_resolve(param_env, uv, Some(span));
         match concrete {
-            Err(ErrorHandled::TooGeneric) => {
-                Err(NotConstEvaluatable::Error(infcx.tcx.sess.delay_span_bug(
-                    span,
-                    format!("Missing value for constant, but no error reported?"),
-                )))
-            }
+            Err(ErrorHandled::TooGeneric) => Err(NotConstEvaluatable::Error(
+                infcx
+                    .tcx
+                    .sess
+                    .delay_span_bug(span, "Missing value for constant, but no error reported?"),
+            )),
             Err(ErrorHandled::Linted) => {
                 let reported = infcx
                     .tcx