#[cfg(backtrace)]
macro_rules! backtrace_if_absent {
    ($err:expr) => {
        match $err.backtrace() {
            Some(_) => None,
            None => Some(Backtrace::capture()),
        }
    };
}
#[cfg(not(backtrace))]
macro_rules! backtrace_if_absent {
    ($err:expr) => {
        None
    };
}

        // Captured here instead of in Error::construct to have one fewer layer
        // of wrapping visible in the backtrace.
        #[cfg(backtrace)]
        let backtrace = match error.backtrace() {
            Some(_) => None,
            None => Some(Backtrace::capture()),
        };
        #[cfg(not(backtrace))]
        let backtrace = None;

        let backtrace = backtrace_if_absent!(error);

    // Takes backtrace as argument rather than capturing it here so that the
    // user sees one fewer layer of wrapping noise in the backtrace.