error[E0594]: cannot assign to `x`, as it is not declared as mutable
  --> $DIR/coroutine-upvar-mutability.rs:10:9
   |
LL |     let x = 0;
   |         - help: consider changing this to be mutable: `mut x`
...
LL |         x = 1;
   |         ^^^^^ cannot assign

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0594`.