failure::format_err! inside try_stream! strange behavior

[serejkaaa512]

If using format_err! macro inside try_stream!:

use failure::*;

pub fn stream() -> impl Stream<Item = failure::Fallible<i32>> + Send {
    async_stream::try_stream! {
        Err(format_err!("adasdasd"))?;
        for i in (1..10) {
            yield 123;
        }
    }
}

It doesn't compile - *mut (dyn std::ops::Fn() + 'static) cannot be shared between threads safely.
But when using it without format_err!:

use failure::*;

#[derive(Debug, Fail)]
#[fail(display = "my error")]
pub struct MyError;

pub fn stream() -> impl Stream<Item = Fallible<i32>> + Send {
    async_stream::try_stream! {
        Err(MyError)?;
        for i in (1..10) {
            yield 123;
        }
    }
}

Compiler says all Ok.

[taiki-e]

failure::format_err! calls format! internally. And std::fmt::Arguments(called by format!) are not implemented Send, so any future containing them will not be implemented Send.

related: rust-lang/rust#64960, rust-lang/rust#64856

[carllerche]

I will close the issue as this is an upstream thing.