error[E0658]: references in constants may only refer to immutable values
  --> $DIR/issue-17718-const-bad-values.rs:1:34
   |
LL | const C1: &'static mut [usize] = &mut [];
   |                                  ^^^^^^^ constants require immutable values
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/57349
   = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable

error[E0013]: constants cannot refer to statics, use a constant instead
  --> $DIR/issue-17718-const-bad-values.rs:5:46
   |
LL | const C2: &'static mut usize = unsafe { &mut S };
   |                                              ^

error[E0658]: references in constants may only refer to immutable values
  --> $DIR/issue-17718-const-bad-values.rs:5:41
   |
LL | const C2: &'static mut usize = unsafe { &mut S };
   |                                         ^^^^^^ constants require immutable values
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/57349
   = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0013, E0658.
For more information about an error, try `rustc --explain E0013`.