rust/tests/ui/macros/panic-temporaries.rs

// check-pass
// edition:2021

#![allow(unreachable_code)]

use std::fmt::{self, Display};
use std::marker::PhantomData;

struct NotSend {
    marker: PhantomData<*const u8>,
}

const NOT_SEND: NotSend = NotSend { marker: PhantomData };

impl Display for NotSend {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_str("this value does not implement Send")
    }
}

async fn f(_: u8) {}

// Exercises this matcher in panic_2021:
// ($($t:tt)+) => $crate::panicking::panic_fmt(...)
async fn panic_fmt() {
    // Panic returns `!`, so the await is never reached, and in particular the
    // temporaries inside the formatting machinery are not still alive at the
    // await point.
    let todo = "...";
    f(panic!("not yet implemented: {}", todo)).await;
}

// Exercises ("{}", $arg:expr) => $crate::panicking::panic_display(&$arg)
async fn panic_display() {
    f(panic!("{}", NOT_SEND)).await;
}

fn require_send(_: impl Send) {}

fn main() {
    require_send(panic_fmt());
    require_send(panic_display());
}