couple of clippy::perf fixes

compiler/rustc_error_messages/src/lib.rs

@@ -299,7 +299,7 @@ impl DiagnosticMessage {
     /// - If `self` is non-translatable then return `self`'s message.
     pub fn with_subdiagnostic_message(&self, sub: SubdiagnosticMessage) -> Self {
         let attr = match sub {
-            SubdiagnosticMessage::Str(s) => return DiagnosticMessage::Str(s.clone()),
+            SubdiagnosticMessage::Str(s) => return DiagnosticMessage::Str(s),
             SubdiagnosticMessage::FluentIdentifier(id) => {
                 return DiagnosticMessage::FluentIdentifier(id, None);
             }

compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs

@@ -212,7 +212,7 @@ impl DiagnosticDeriveBuilder {
                 }
                 NestedMeta::Meta(meta @ Meta::NameValue(_))
                     if !is_help_note_or_warn
-                        && meta.path().segments.last().unwrap().ident.to_string() == "code" =>
+                        && meta.path().segments.last().unwrap().ident == "code" =>
                 {
                     // don't error for valid follow-up attributes
                 }

compiler/rustc_macros/src/diagnostics/fluent.rs

@@ -194,8 +194,8 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
                 let snake_name = Ident::new(
                     // FIXME: should probably trim prefix, not replace all occurrences
                     &name
-                        .replace(&format!("{}-", res.ident).replace("_", "-"), "")
-                        .replace("-", "_"),
+                        .replace(&format!("{}-", res.ident).replace('_', "-"), "")
+                        .replace('-', "_"),
                     span,
                 );
                 constants.extend(quote! {
@@ -207,7 +207,7 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
                 });
 
                 for Attribute { id: Identifier { name: attr_name }, .. } in attributes {
-                    let snake_name = Ident::new(&attr_name.replace("-", "_"), span);
+                    let snake_name = Ident::new(&attr_name.replace('-', "_"), span);
                     if !previous_attrs.insert(snake_name.clone()) {
                         continue;
                     }

compiler/rustc_middle/src/ty/consts/valtree.rs

@@ -88,19 +88,17 @@ impl<'tcx> ValTree<'tcx> {
                     let leafs = self
                         .unwrap_branch()
                         .into_iter()
-                        .map(|v| v.unwrap_leaf().try_to_u8().unwrap())
-                        .collect::<Vec<_>>();
+                        .map(|v| v.unwrap_leaf().try_to_u8().unwrap());
 
-                    return Some(tcx.arena.alloc_from_iter(leafs.into_iter()));
+                    return Some(tcx.arena.alloc_from_iter(leafs));
                 }
                 ty::Slice(slice_ty) if *slice_ty == tcx.types.u8 => {
                     let leafs = self
                         .unwrap_branch()
                         .into_iter()
-                        .map(|v| v.unwrap_leaf().try_to_u8().unwrap())
-                        .collect::<Vec<_>>();
+                        .map(|v| v.unwrap_leaf().try_to_u8().unwrap());
 
-                    return Some(tcx.arena.alloc_from_iter(leafs.into_iter()));
+                    return Some(tcx.arena.alloc_from_iter(leafs));
                 }
                 _ => {}
             },

compiler/rustc_privacy/src/lib.rs

@@ -1754,7 +1754,6 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
                 || self.in_assoc_ty
                 || self.tcx.resolutions(()).has_pub_restricted
             {
-                let descr = descr.to_string();
                 let vis_span =
                     self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id));
                 if kind == "trait" {

compiler/rustc_resolve/src/diagnostics.rs

@@ -2608,7 +2608,7 @@ fn show_candidates(
                 "item".to_string()
             };
             let plural_descr =
-                if descr.ends_with("s") { format!("{}es", descr) } else { format!("{}s", descr) };
+                if descr.ends_with('s') { format!("{}es", descr) } else { format!("{}s", descr) };
 
             let mut msg = format!("{}these {} exist but are inaccessible", prefix, plural_descr);
             let mut has_colon = false;

compiler/rustc_session/src/options.rs

@@ -535,7 +535,7 @@ mod parse {
     ) -> bool {
         match v {
             Some(s) => {
-                for s in s.split(",") {
+                for s in s.split(',') {
                     let Some(pass_name) = s.strip_prefix(&['+', '-'][..]) else { return false };
                     slot.push((pass_name.to_string(), &s[..1] == "+"));
                 }

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -607,10 +607,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                                 "{}, {}={}>",
                                 &constraint[..constraint.len() - 1],
                                 item.name,
-                                term.to_string()
+                                term
                             );
                         } else {
-                            constraint.push_str(&format!("<{}={}>", item.name, term.to_string()));
+                            constraint.push_str(&format!("<{}={}>", item.name, term));
                         }
                     }
 

compiler/rustc_typeck/src/check/expr.rs

@@ -1803,7 +1803,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .source_map()
                 .span_to_snippet(range_end.expr.span)
                 .map(|s| format!(" from `{s}`"))
-                .unwrap_or(String::new());
+                .unwrap_or_default();
             err.span_suggestion(
                 range_start.span.shrink_to_hi(),
                 &format!("to set the remaining fields{instead}, separate the last named field with a comma"),
@@ -2362,7 +2362,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 false
             };
         let expr_snippet =
-            self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or(String::new());
+            self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or_default();
         let is_wrapped = expr_snippet.starts_with('(') && expr_snippet.ends_with(')');
         let after_open = expr.span.lo() + rustc_span::BytePos(1);
         let before_close = expr.span.hi() - rustc_span::BytePos(1);

compiler/rustc_typeck/src/check/generator_interior/drop_ranges/record_consumed_borrow.rs

@@ -72,9 +72,8 @@ impl<'tcx> ExprUseDelegate<'tcx> {
     }
 
     fn mark_consumed(&mut self, consumer: HirId, target: TrackedValue) {
-        if !self.places.consumed.contains_key(&consumer) {
-            self.places.consumed.insert(consumer, <_>::default());
-        }
+        self.places.consumed.entry(consumer).or_insert_with(|| <_>::default());
+
         debug!(?consumer, ?target, "mark_consumed");
         self.places.consumed.get_mut(&consumer).map(|places| places.insert(target));
     }