warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/issue-63716-parse-async.rs:7:12
   |
LL | #![feature(specialization)]
   |            ^^^^^^^^^^^^^^
   |
   = note: `#[warn(incomplete_features)]` on by default
   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information

warning: 1 warning emitted

