warning: encountered mutable pointer in final value of constant
  --> $DIR/future-incompat-mutable-in-final-value-issue-121610.rs:13:1
   |
LL | const UNDEFINED: &JsValue = &JsValue::Undefined;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
   = note: `#[warn(const_eval_mutable_ptr_in_final_value)]` on by default

warning: 1 warning emitted

Future incompatibility report: Future breakage diagnostic:
warning: encountered mutable pointer in final value of constant
  --> $DIR/future-incompat-mutable-in-final-value-issue-121610.rs:13:1
   |
LL | const UNDEFINED: &JsValue = &JsValue::Undefined;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
   = note: `#[warn(const_eval_mutable_ptr_in_final_value)]` on by default