Avoid allocating unnecessarily

Author: blyxyas

clippy_lints/src/unit_return_expecting_ord.rs

@@ -5,7 +5,7 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_middle::ty::{ClauseKind, GenericPredicates, ProjectionPredicate, TraitPredicate};
 use rustc_session::declare_lint_pass;
-use rustc_span::{BytePos, Span, sym};
+use rustc_span::{BytePos, Span, Symbol, sym};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -86,7 +86,7 @@ fn get_args_to_check<'tcx>(
     fn_mut_trait: DefId,
     ord_trait: Option<DefId>,
     partial_ord_trait: Option<DefId>,
-) -> Vec<(usize, String)> {
+) -> Vec<(usize, Symbol)> {
     let mut args_to_check = Vec::new();
     if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
         let fn_sig = cx.tcx.fn_sig(def_id).instantiate_identity();
@@ -116,15 +116,15 @@ fn get_args_to_check<'tcx>(
                             .iter()
                             .any(|ord| Some(ord.self_ty()) == return_ty_pred.term.as_type())
                         {
-                            args_to_check.push((i, String::from("Ord")));
+                            args_to_check.push((i, sym::Ord));
                             if args_to_check.len() == args_len - 1 {
                                 break;
                             }
                         } else if partial_ord_preds
                             .iter()
                             .any(|pord| pord.self_ty() == return_ty_pred.term.expect_type())
                         {
-                            args_to_check.push((i, String::from("PartialOrd")));
+                            args_to_check.push((i, sym::PartialOrd));
                             if args_to_check.len() == args_len - 1 {
                                 break;
                             }
@@ -188,7 +188,8 @@ impl<'tcx> LateLintPass<'tcx> for UnitReturnExpectingOrd {
                             span,
                             format!(
                                 "this closure returns \
-                                   the unit type which also implements {trait_name}"
+                                   the unit type which also implements {}",
+                                trait_name.as_str()
                             ),
                         );
                     },
@@ -199,7 +200,8 @@ impl<'tcx> LateLintPass<'tcx> for UnitReturnExpectingOrd {
                             span,
                             format!(
                                 "this closure returns \
-                                   the unit type which also implements {trait_name}"
+                                   the unit type which also implements {}",
+                                trait_name.as_str()
                             ),
                             Some(last_semi),
                             "probably caused by this trailing semicolon",