Fixme with link for re-enabling const mutation lint for Drop consts

Author: dtolnay

compiler/rustc_mir/src/transform/check_const_item_mutation.rs

@@ -39,14 +39,21 @@ impl<'a, 'tcx> ConstMutationChecker<'a, 'tcx> {
         // We avoid linting mutation of a const item if the const's type has a
         // Drop impl. The Drop logic observes the mutation which was performed.
         //
-        //     struct Log { msg: &'static str }
-        //     const LOG: Log = Log { msg: "" };
+        //     pub struct Log { msg: &'static str }
+        //     pub const LOG: Log = Log { msg: "" };
         //     impl Drop for Log {
         //         fn drop(&mut self) { println!("{}", self.msg); }
         //     }
         //
         //     LOG.msg = "wow";  // prints "wow"
         //
+        // FIXME(https://github.com/rust-lang/rust/issues/77425):
+        // Drop this exception once there is a stable attribute to suppress the
+        // const item mutation lint for a single specific const only. Something
+        // equivalent to:
+        //
+        //     #[const_mutation_allowed]
+        //     pub const LOG: Log = Log { msg: "" };
         match self.tcx.calculate_dtor(def_id, &mut any_dtor) {
             Some(_) => None,
             None => Some(def_id),