Note ref expr being cast when encounter NonScalar cast error

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

1 files changed, 10 insertions, 0 deletions

diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index c044c4f7c37..e144a6ab599 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -408,6 +408,16 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                     self.expr_ty,
                     fcx.ty_to_string(self.cast_ty)
                 );
+
+                if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span)
+                    && matches!(self.expr.kind, ExprKind::AddrOf(..))
+                {
+                    err.note(format!(
+                        "casting reference expression `{}` because `&` binds tighter than `as`",
+                        snippet
+                    ));
+                }
+
                 let mut sugg = None;
                 let mut sugg_mutref = false;
                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {