error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
  --> $DIR/issue-100313.rs:10:13
   |
LL |             *(B as *const bool as *mut bool) = false;
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[deny(cast_ref_to_mut)]` on by default

error[E0080]: evaluation of constant value failed
  --> $DIR/issue-100313.rs:10:13
   |
LL |             *(B as *const bool as *mut bool) = false;
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ writing to alloc7 which is read-only
   |
note: inside `T::<&true>::set_false`
  --> $DIR/issue-100313.rs:10:13
   |
LL |             *(B as *const bool as *mut bool) = false;
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: inside `_`
  --> $DIR/issue-100313.rs:19:5
   |
LL |     x.set_false();
   |     ^^^^^^^^^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0080`.