Fix the issue of invalid suggestion for a reference of iterator

Author: chenyukang

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1284,6 +1284,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         if self.in_move_closure(expr) {
             return false;
         }
+
         // Try to find predicates on *generic params* that would allow copying `ty`
         let mut suggestion =
             if let Some(symbol) = tcx.hir().maybe_get_struct_pattern_shorthand_field(expr) {

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

@@ -466,7 +466,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             && 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;
@@ -553,6 +552,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         );
                         if self.predicate_may_hold(&obligation)
                             && self.predicate_must_hold_modulo_regions(&sized_obligation)
+                            // Do not suggest * if it is already a reference,
+                            // will suggest removing the borrow instead in that case.
+                            && !matches!(expr.kind, hir::ExprKind::AddrOf(..))
                         {
                             let call_node = self.tcx.hir_node(*call_hir_id);
                             let msg = "consider dereferencing here";

tests/ui/traits/suggest-dereferences/invalid-suggest-deref-issue-127590.stderr

@@ -10,10 +10,6 @@ LL |     for (src, dest) in std::iter::zip(fields.iter(), &variant.iter()) {
    = note: required for `&std::slice::Iter<'_, {integer}>` to implement `IntoIterator`
 note: required by a bound in `std::iter::zip`
   --> $SRC_DIR/core/src/iter/adapters/zip.rs:LL:COL
-help: consider dereferencing here
-   |
-LL |     for (src, dest) in std::iter::zip(fields.iter(), *&variant.iter()) {
-   |                                                      +
 help: consider removing the leading `&`-reference
    |
 LL -     for (src, dest) in std::iter::zip(fields.iter(), &variant.iter()) {
@@ -43,10 +39,6 @@ LL |     for (src, dest) in std::iter::zip(fields.iter(), &variant.iter().clone(
    = note: required for `&std::slice::Iter<'_, {integer}>` to implement `IntoIterator`
 note: required by a bound in `std::iter::zip`
   --> $SRC_DIR/core/src/iter/adapters/zip.rs:LL:COL
-help: consider dereferencing here
-   |
-LL |     for (src, dest) in std::iter::zip(fields.iter(), *&variant.iter().clone()) {
-   |                                                      +
 help: consider removing the leading `&`-reference
    |
 LL -     for (src, dest) in std::iter::zip(fields.iter(), &variant.iter().clone()) {