Remove another use of clone_code

Author: oli-obk

compiler/rustc_typeck/src/check/fn_ctxt/checks.rs

@@ -12,7 +12,6 @@ use crate::check::{
 use crate::structured_errors::StructuredDiagnostic;
 
 use rustc_ast as ast;
-use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Applicability, Diagnostic, DiagnosticId, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
@@ -1601,24 +1600,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Peel derived obligation, because it's the type that originally
             // started this inference chain that matters, not the one we wound
             // up with at the end.
-            fn unpeel_to_top(
-                mut code: Lrc<ObligationCauseCode<'_>>,
-            ) -> Lrc<ObligationCauseCode<'_>> {
-                let mut result_code = code.clone();
+            fn unpeel_to_top<'a, 'tcx>(
+                mut code: &'a ObligationCauseCode<'tcx>,
+            ) -> &'a ObligationCauseCode<'tcx> {
+                let mut result_code = code;
                 loop {
-                    let parent = match &*code {
-                        ObligationCauseCode::ImplDerivedObligation(c) => {
-                            c.derived.parent_code.clone()
-                        }
+                    let parent = match code {
+                        ObligationCauseCode::ImplDerivedObligation(c) => &c.derived.parent_code,
                         ObligationCauseCode::BuiltinDerivedObligation(c)
-                        | ObligationCauseCode::DerivedObligation(c) => c.parent_code.clone(),
-                        _ => break,
+                        | ObligationCauseCode::DerivedObligation(c) => &c.parent_code,
+                        _ => break result_code,
                     };
-                    result_code = std::mem::replace(&mut code, parent);
+                    (result_code, code) = (code, parent);
                 }
-                result_code
             }
-            let self_: ty::subst::GenericArg<'_> = match &*unpeel_to_top(error.obligation.cause.clone_code()) {
+            let self_: ty::subst::GenericArg<'_> = match unpeel_to_top(error.obligation.cause.code()) {
                 ObligationCauseCode::BuiltinDerivedObligation(code) |
                 ObligationCauseCode::DerivedObligation(code) => {
                     code.parent_trait_pred.self_ty().skip_binder().into()