warning: unused closure that must be used
  --> $DIR/issue-16256.rs:6:5
   |
LL |     |c: u8| buf.push(c);
   |     ^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_must_use)]` on by default
   = note: closures are lazy and do nothing unless called

warning: 1 warning emitted

