Rollup merge of #106891 - estebank:issue-45727, r=petrochenkov

Tweak "borrow closure argument" suggestion

Fix #45727.

2 files changed, 26 insertions, 8 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 434f75de02b..52971486c55 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -1350,6 +1350,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         expected_trait_ref,
                         obligation.cause.code(),
                         found_node,
+                        obligation.param_env,
                     )
                 } else {
                     let (closure_span, closure_arg_span, found) = found_did
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 195bbe92f8b..39e50b2accf 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -283,6 +283,7 @@ pub trait TypeErrCtxtExt<'tcx> {
         expected: ty::PolyTraitRef<'tcx>,
         cause: &ObligationCauseCode<'tcx>,
         found_node: Option<Node<'_>>,
+        param_env: ty::ParamEnv<'tcx>,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
 
     fn note_conflicting_closure_bounds(
@@ -1978,6 +1979,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         expected: ty::PolyTraitRef<'tcx>,
         cause: &ObligationCauseCode<'tcx>,
         found_node: Option<Node<'_>>,
+        param_env: ty::ParamEnv<'tcx>,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         pub(crate) fn build_fn_sig_ty<'tcx>(
             infcx: &InferCtxt<'tcx>,
@@ -2040,7 +2042,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         self.note_conflicting_closure_bounds(cause, &mut err);
 
         if let Some(found_node) = found_node {
-            hint_missing_borrow(span, found, expected, found_node, &mut err);
+            hint_missing_borrow(self, param_env, span, found, expected, found_node, &mut err);
         }
 
         err
@@ -3747,6 +3749,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
 /// Add a hint to add a missing borrow or remove an unnecessary one.
 fn hint_missing_borrow<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
     span: Span,
     found: Ty<'tcx>,
     expected: Ty<'tcx>,
@@ -3769,7 +3773,7 @@ fn hint_missing_borrow<'tcx>(
     // This could be a variant constructor, for example.
     let Some(fn_decl) = found_node.fn_decl() else { return; };
 
-    let arg_spans = fn_decl.inputs.iter().map(|ty| ty.span);
+    let args = fn_decl.inputs.iter().map(|ty| ty);
 
     fn get_deref_type_and_refs(mut ty: Ty<'_>) -> (Ty<'_>, usize) {
         let mut refs = 0;
@@ -3785,21 +3789,34 @@ fn hint_missing_borrow<'tcx>(
     let mut to_borrow = Vec::new();
     let mut remove_borrow = Vec::new();
 
-    for ((found_arg, expected_arg), arg_span) in found_args.zip(expected_args).zip(arg_spans) {
+    for ((found_arg, expected_arg), arg) in found_args.zip(expected_args).zip(args) {
         let (found_ty, found_refs) = get_deref_type_and_refs(*found_arg);
         let (expected_ty, expected_refs) = get_deref_type_and_refs(*expected_arg);
 
-        if found_ty == expected_ty {
+        if infcx.can_eq(param_env, found_ty, expected_ty).is_ok() {
             if found_refs < expected_refs {
-                to_borrow.push((arg_span, expected_arg.to_string()));
+                to_borrow.push((arg.span.shrink_to_lo(), "&".repeat(expected_refs - found_refs)));
             } else if found_refs > expected_refs {
-                remove_borrow.push((arg_span, expected_arg.to_string()));
+                let mut span = arg.span.shrink_to_lo();
+                let mut left = found_refs - expected_refs;
+                let mut ty = arg;
+                while let hir::TyKind::Ref(_, mut_ty) = &ty.kind && left > 0 {
+                    span = span.with_hi(mut_ty.ty.span.lo());
+                    ty = mut_ty.ty;
+                    left -= 1;
+                }
+                let sugg = if left == 0 {
+                    (span, String::new())
+                } else {
+                    (arg.span, expected_arg.to_string())
+                };
+                remove_borrow.push(sugg);
             }
         }
     }
 
     if !to_borrow.is_empty() {
-        err.multipart_suggestion(
+        err.multipart_suggestion_verbose(
             "consider borrowing the argument",
             to_borrow,
             Applicability::MaybeIncorrect,
@@ -3807,7 +3824,7 @@ fn hint_missing_borrow<'tcx>(
     }
 
     if !remove_borrow.is_empty() {
-        err.multipart_suggestion(
+        err.multipart_suggestion_verbose(
             "do not borrow the argument",
             remove_borrow,
             Applicability::MaybeIncorrect,