async-await: [WIP] replace std await! macro with await syntax

[taiki-e]

Motivation

await syntax was implemented in rust-lang/rust#60586, and nightly-2019-05-09 has been released with the changes. Also, await! macro will be removed in the future.

Solution

await syntax only works in the 2018 edition, so this PR has not replaced some std await! macros yet (it needs to bump the minimum support version).

This PR currently uses a way that does not bump the minimum supported version, but this is blocked by std::r#await! macro not working (see rust-lang/rust#60660).

cc @carllerche @davidbarsky

[taiki-e]

By the way, should we rename tokio::r#await! macro?

[davidbarsky]

Thanks for opening this! We were thinking of having a compat! macro that does the into_awaitable dance in addition to a the replacement of the await! macro. Naming: I think we were gonna go with async_wait! or wait!—do you have any opinions?

[carllerche]

I think we will have to remove tokio-futures from the main workspace and move it into a separate one (similar to the async-await dir) so that it can be switched to 2018.

[carllerche]

Alternatively, we fork off 0.1 and leave it as is and start updating master...

[cramertj]

I think we will have to remove tokio-futures from the main workspace and move it into a separate one (similar to the async-await dir) so that it can be switched to 2018.

Sorry if i'm skipping some detail here-- it should be possible to update only that one crate to 2018 without moving it to a separate workspace.

[taiki-e]

@cramertj

I think we will have to remove tokio-futures from the main workspace and move it into a separate one (similar to the async-await dir) so that it can be switched to 2018.

Sorry if i'm skipping some detail here-- it should be possible to update only that one crate to 2018 without moving it to a separate workspace.

It probably can only be done with Rust 1.31 or later. See also #935 (comment).

[carllerche]

@cramertj maybe? I remember trying that initially, but hit problems...

[taiki-e]

I added some commits. Hopefully, after #1082 is merged, just merge the master into this PR and CI will success.

[carllerche]

Thanks for this ❤️ I pulled this PR into #1082, so I will close this.