Some simple clippy::perf fixes

compiler/rustc_data_structures/src/profiling.rs

@@ -778,7 +778,7 @@ pub fn print_time_passes_entry(
                 "rss_start": start_rss,
                 "rss_end": end_rss,
             });
-            eprintln!("time: {}", json.to_string());
+            eprintln!("time: {}", json);
             return;
         }
         TimePassesFormat::Text => (),

compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs

@@ -242,8 +242,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let Some(arg) = segment
             .args()
             .args
-            .iter()
-            .nth(index) else { return false; };
+            .get(index) else { return false; };
         error.obligation.cause.span = arg
             .span()
             .find_ancestor_in_same_ctxt(error.obligation.cause.span)

compiler/rustc_macros/src/diagnostics/fluent.rs

@@ -100,7 +100,7 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
             Diagnostic::spanned(
                 resource_span,
                 Level::Error,
-                format!("could not open Fluent resource: {}", e.to_string()),
+                format!("could not open Fluent resource: {}", e),
             )
             .emit();
             return failed(&crate_name);

compiler/rustc_resolve/src/late.rs

@@ -1224,7 +1224,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             lifetime_ribs: Vec::new(),
             lifetime_elision_candidates: None,
             current_trait_ref: None,
-            diagnostic_metadata: Box::new(DiagnosticMetadata::default()),
+            diagnostic_metadata: Box::<DiagnosticMetadata<'_>>::default(),
             // errors at module scope should always be reported
             in_func_body: false,
             lifetime_uses: Default::default(),

compiler/rustc_transmute/src/lib.rs

@@ -149,7 +149,7 @@ mod rustc {
                     .iter()
                     .enumerate()
                     .find(|(_, field_def)| name == field_def.name)
-                    .expect(&format!("There were no fields named `{name}`."));
+                    .unwrap_or_else(|| panic!("There were no fields named `{name}`."));
                 fields[field_idx].unwrap_leaf() == ScalarInt::TRUE
             };