error[E0658]: casting pointers to integers in constants is unstable
  --> $DIR/issue-18294.rs:3:31
   |
LL |     const Y: usize = unsafe { &X as *const u32 as usize };
   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/51910
   = help: add `#![feature(const_raw_ptr_to_usize_cast)]` to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.