Perform Ok-wrapping in try_block macro

[joseph-gio]

This modifies the macro to perform Ok-wrapping on the final value. Not only is this more ergonomic, this is how the full try block feature will behave when it is eventually stabilized: rust-lang/rust#70941. Since this macro is meant to emulate the try block feature while we wait for stabilization, it makes sense that it should try to behave as closely to that feature as possible.

This will obviously be a breaking change, but since the crate has not reached 1.0 yet, that should not be a problem.

[scottmcm]

You can actually avoid the need for this trait with a bit of trickery. Try::from_output is unstable, but you can get to it via try_fold: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=0b07b516d97996ac386886ee21d8c561

macro_rules! do_ok_wrapping {
    ($e:expr) => {
        std::iter::empty()
            .try_fold($e, |_, ()| unreachable!())
    };
}

fn main() {
    let _: Option<i32> = do_ok_wrapping!(3);
    let _: std::io::Result<i32> = do_ok_wrapping!(5);
}

(That might make the error messages horrible, though.)

[joseph-gio]

You can even remove the panic by using the never type instead of unit.

std::iter::empty()
    .try_fold($e, |_, x: !| match x { })

I think this repo is unmaintained so I'm going to fork it, and I'll definitely use your idea.

[scottmcm]

Oh, nice touch! An uninhabited enum -- no need for ! specifically -- is a great idea.