Improve comment phrasing

Co-authored-by: oliver <[email protected]>

Author: sjwang05

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

@@ -724,6 +724,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             && let hir::Node::Expr(expr) = self.tcx.hir().get(*arg_hir_id)
             && let Some(arg_ty) = typeck_results.expr_ty_adjusted_opt(expr)
         {
+            // Suggest dereferencing the argument to a function/method call if possible
+
             let mut real_trait_pred = trait_pred;
             while let Some((parent_code, parent_trait_pred)) = code.parent() {
                 code = parent_code;
@@ -763,7 +765,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     {
                         if steps > 0 {
                             // Don't care about `&mut` because `DerefMut` is used less
-                            // often and user will not expect autoderef happens.
+                            // often and user will not expect that an autoderef happens.
                             if let Some(hir::Node::Expr(hir::Expr {
                                 kind:
                                     hir::ExprKind::AddrOf(
@@ -850,6 +852,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             && let hir::Node::Expr(rhs) = self.tcx.hir().get(*rhs_hir_id)
             && let Some(rhs_ty) = typeck_results.expr_ty_opt(rhs)
         {
+            // Suggest dereferencing the LHS, RHS, or both terms of a binop if possible
+
             let trait_pred = predicate.unwrap_or(trait_pred);
             let lhs_ty = self.tcx.instantiate_bound_regions_with_erased(trait_pred.self_ty());
             let lhs_autoderef = (self.autoderef_steps)(lhs_ty);
@@ -869,6 +873,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 .rev();
             if let Some((lsteps, rsteps)) =
                 autoderefs.find_map(|((lsteps, (l_ty, _)), (rsteps, (r_ty, _)))| {
+                    // Create a new predicate with the dereferenced LHS and RHS
+                    // We simultaneously dereference both sides rather than doing them
+                    // one at a time to account for cases such as &Box<T> == &&T
                     let trait_pred_and_ty = trait_pred.map_bound(|inner| {
                         (
                             ty::TraitPredicate {
@@ -909,6 +916,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         expr = inner;
                         steps -= 1;
                     }
+                    // Empty suggestions with empty spans ICE with debug assertions
                     if steps == 0 {
                         return (
                             msg.trim_end_matches(" and dereferencing instead"),
@@ -936,6 +944,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             format!("{derefs}"),
                         )]
                     };
+                    // Empty suggestions with empty spans ICE with debug assertions
                     if !prefix_span.is_empty() {
                         suggestion.push((prefix_span, String::new()));
                     }