Format tokio::select! with rustfmt

[dbrgn]

Is your feature request related to a problem? Please describe.

The tokio::select! macro is something used quite often in real-world code. However, rustfmt cannot format code inside that call.

Describe the solution you'd like

Maybe it would be possible to adjust the macro so that the code can be formatted with rustfmt?

I found a project here which plays with alternative syntax to enable this. (Pinging @jkelleyrtp)

Describe alternatives you've considered

Alternatively, maybe rustfmt could be changed to support the current syntax? Not sure if that's possible, since macros can have quite diverse syntax.

Related issue: rust-lang/rustfmt#8

[Darksonn]

Although this would be very nice, we cannot change the syntax used by the macro.

[Darksonn]

I'm going to close this. As it currently stands, this is not actionable for us. Feel free to reopen or open a new issue if a change in rustfmt makes this possible in the future.

[dbrgn]

The best workaround is probably to move the branch code into a standalone function, and call it from the macro. That way, the function can be formatted.

[Darksonn]

I'm not sure I understand your suggestion.

[dbrgn]

The problem is that in this example:

    tokio::select! {
        val = rx1 => {
            println!("rx1 completed first with {:?}", val);
            // do some other stuff with rx1
        }
        val = rx2 => {
            println!("rx2 completed first with {:?}", val);
            // do some other stuff with rx2
        }
    }

...the code in the branches is not formatted by rustfmt, because it is inside the select! macro.

By moving the code into separate functions outside the macro:

    tokio::select! {
        val = rx1 => {
            println!("rx1 completed first with {:?}", val);
            handle_rx1(val)
        }
        val = rx2 => {
            println!("rx2 completed first with {:?}", val);
            handle_rx2(val)
        }
    }

    fn handle_rx1(val: ...): void {
        // do some stuff with rx1
    }

    fn handle_rx2(val: ...): void {
        // do some stuff with rx2
    }

...the functions can be formatted correctly.

[lfpraca]

I found that a decent solution is to put #[rustfmt::skip] on top of the tokio::select! macro and format the code inside the macro using functionality from a code editor