3 files changed, 31 insertions, 9 deletions
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index 95f0b651962..f482e3d7c12 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -318,7 +318,10 @@ lint_invalid_nan_comparisons_eq_ne = incorrect NaN comparison, NaN cannot be dir
 
 lint_invalid_nan_comparisons_lt_le_gt_ge = incorrect NaN comparison, NaN is not orderable
 
-lint_invalid_reference_casting = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
+lint_invalid_reference_casting_assign_to_ref = assigning to `&T` is undefined behavior, consider using an `UnsafeCell`
+    .label = casting happend here
+
+lint_invalid_reference_casting_borrow_as_mut = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
     .label = casting happend here
 
 lint_lintpass_by_hand = implementing `LintPass` by hand
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 6d774070ec4..a6a48bf4ffa 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -745,10 +745,17 @@ pub enum InvalidFromUtf8Diag {
 
 // reference_casting.rs
 #[derive(LintDiagnostic)]
-#[diag(lint_invalid_reference_casting)]
-pub struct InvalidReferenceCastingDiag {
-    #[label]
-    pub orig_cast: Option<Span>,
+pub enum InvalidReferenceCastingDiag {
+    #[diag(lint_invalid_reference_casting_borrow_as_mut)]
+    BorrowAsMut {
+        #[label]
+        orig_cast: Option<Span>,
+    },
+    #[diag(lint_invalid_reference_casting_assign_to_ref)]
+    AssignToRef {
+        #[label]
+        orig_cast: Option<Span>,
+    },
 }
 
 // hidden_unicode_codepoints.rs
diff --git a/compiler/rustc_lint/src/reference_casting.rs b/compiler/rustc_lint/src/reference_casting.rs
index 428bf750bbd..ed3d4721049 100644
--- a/compiler/rustc_lint/src/reference_casting.rs
+++ b/compiler/rustc_lint/src/reference_casting.rs
@@ -73,13 +73,25 @@ impl<'tcx> LateLintPass<'tcx> for InvalidReferenceCasting {
             return;
         };
 
-        if is_cast_from_const_to_mut(cx, e) {
-            cx.emit_spanned_lint(INVALID_REFERENCE_CASTING, expr.span, InvalidReferenceCastingDiag { orig_cast: None });
+        let orig_cast = if is_cast_from_const_to_mut(cx, e) {
+            None
         } else if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind
             && let Res::Local(hir_id) = &path.res
             && let Some(orig_cast) = self.casted.get(hir_id) {
-            cx.emit_spanned_lint(INVALID_REFERENCE_CASTING, expr.span, InvalidReferenceCastingDiag { orig_cast: Some(*orig_cast) });
-        }
+            Some(*orig_cast)
+        } else {
+            return;
+        };
+
+        cx.emit_spanned_lint(
+            INVALID_REFERENCE_CASTING,
+            expr.span,
+            if matches!(expr.kind, ExprKind::AddrOf(..)) {
+                InvalidReferenceCastingDiag::BorrowAsMut { orig_cast }
+            } else {
+                InvalidReferenceCastingDiag::AssignToRef { orig_cast }
+            },
+        );
     }
 }