error[E0435]: attempt to use a non-constant value in a constant
  --> $DIR/issue-3668-2.rs:4:27
   |
LL |     static child: isize = x + 1;
   |                           ^ non-constant value
   |
help: consider using `let` instead of `static`
   |
LL -     static child: isize = x + 1;
LL +     let child: isize = x + 1;
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0435`.