error[E0382]: use of moved value: `blk`
  --> $DIR/once-cant-call-twice-on-heap.rs:9:5
   |
LL | fn foo<F:FnOnce()>(blk: F) {
   |        -           --- move occurs because `blk` has type `F`, which does not implement the `Copy` trait
   |        |
   |        consider adding a `Copy` constraint to this type argument
LL |     blk();
   |     --- value moved here
LL |     blk();
   |     ^^^ value used here after move

error: aborting due to previous error

For more information about this error, try `rustc --explain E0382`.