const fn: Missing tracking issue and feature gate name in stability error messages #57261

error: function pointers in const fn are unstable
 --> a.rs:1:26
  |
1 | const fn foo(x: fn()) -> fn() { x }
  |                          ^^^^

error: aborting due to previous error

error[E0658]: box expression syntax is experimental; you can call `Box::new` instead. (see issue #49733)
 --> a.rs:1:24
  |
1 | fn foo() -> Box<u32> { box 4 }
  |                        ^^^^^
  |
  = help: add #![feature(box_syntax)] to the crate attributes to enable

error: aborting due to previous error