error[E0658]: let bindings in constant functions are unstable (see issue #48821)
  --> $DIR/feature-gate-const_let.rs:16:13
   |
LL |     let x = 42;
   |             ^^
   |
   = help: add #![feature(const_let)] to the crate attributes to enable

error[E0658]: statements in constant functions are unstable (see issue #48821)
  --> $DIR/feature-gate-const_let.rs:16:13
   |
LL |     let x = 42;
   |             ^^
   |
   = help: add #![feature(const_let)] to the crate attributes to enable

error: aborting due to 2 previous errors

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