Macro debug_assert_ready_err

macro_rules! debug_assert_ready_err {
    ($($arg:tt)*) => { ... };
}

Asserts that the expression matches a Poll::Ready(Err(_)) variant on debug builds.

This macro behaves nearly the same as assert_ready_err! on debug builds, although it does not return the value contained in the Poll::Ready(Err(_)) variant. On release builds it is a no-op.