Rollup merge of #106497 - chenyukang:yukang/fix-106443-sugg-clone, r=estebank

Suggest using clone when we have &T and T implemented Clone

Fixes #106443

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

@@ -873,6 +873,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             );
                         }
 
+                        if self.suggest_add_clone_to_arg(&obligation, &mut err, trait_predicate) {
+                            err.emit();
+                            return;
+                        }
+
                         if self.suggest_impl_trait(&mut err, span, &obligation, trait_predicate) {
                             err.emit();
                             return;

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

@@ -10,7 +10,7 @@ use crate::infer::InferCtxt;
 use crate::traits::{NormalizeExt, ObligationCtxt};
 
 use hir::def::CtorOf;
-use hir::HirId;
+use hir::{Expr, HirId};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{
@@ -206,6 +206,13 @@ pub trait TypeErrCtxtExt<'tcx> {
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     );
 
+    fn suggest_add_clone_to_arg(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut Diagnostic,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
+    ) -> bool;
+
     fn suggest_add_reference_to_arg(
         &self,
         obligation: &PredicateObligation<'tcx>,
@@ -1102,6 +1109,55 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         }
     }
 
+    fn suggest_add_clone_to_arg(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut Diagnostic,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
+    ) -> bool {
+        let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
+        let ty = self.tcx.erase_late_bound_regions(self_ty);
+        let owner = self.tcx.hir().get_parent_item(obligation.cause.body_id);
+        let Some(generics) = self.tcx.hir().get_generics(owner.def_id) else { return false };
+        let ty::Ref(_, inner_ty, hir::Mutability::Not) = ty.kind() else { return false };
+        let ty::Param(param) = inner_ty.kind() else { return false };
+        let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, .. } = obligation.cause.code() else { return false };
+        let arg_node = self.tcx.hir().get(*arg_hir_id);
+        let Node::Expr(Expr { kind: hir::ExprKind::Path(_), ..}) = arg_node else { return false };
+
+        let clone_trait = self.tcx.require_lang_item(LangItem::Clone, None);
+        let has_clone = |ty| {
+            self.type_implements_trait(clone_trait, [ty], obligation.param_env)
+                .must_apply_modulo_regions()
+        };
+
+        let new_obligation = self.mk_trait_obligation_with_new_self_ty(
+            obligation.param_env,
+            trait_pred.map_bound(|trait_pred| (trait_pred, *inner_ty)),
+        );
+
+        if self.predicate_may_hold(&new_obligation) && has_clone(ty) {
+            if !has_clone(param.to_ty(self.tcx)) {
+                suggest_constraining_type_param(
+                    self.tcx,
+                    generics,
+                    err,
+                    param.name.as_str(),
+                    "Clone",
+                    Some(clone_trait),
+                );
+            }
+            err.span_suggestion_verbose(
+                obligation.cause.span.shrink_to_hi(),
+                "consider using clone here",
+                ".clone()".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+            return true;
+        }
+        false
+    }
+
     fn suggest_add_reference_to_arg(
         &self,
         obligation: &PredicateObligation<'tcx>,