Tracking Issue for the 2024 prelude

[Noratrieb]

Feature gate: #![feature(prelude_2024)]

This is a tracking issue for the 2024 prelude.

Public API

The 2024 prelude contains the following items in addition to all items in the 2024 prelude:

• core::future::{Future, IntoFuture}: RFC 3509 RFC: Include Future and IntoFuture in the 2024 prelude rfcs#3509

// core::prelude

pub mod rust_2024 {
    pub use super::rust_2021::*;
    pub use crate::future::{Future, IntoFuture};
}

And removes RustcEncodable, and RustcDecodable:

• Built-in derive macros Encodable, Decodable, RustcEncodable and RustcDecodable are stable #62048

Steps

• Implement in nightly Rust 2024 (Future, IntoFuture).
  • Add Future and IntoFuture to the 2024 prelude #121041
• Implement in nightly Rust 2024 (RustcEncodeable, RustcDecodable).
  • Soft-destabilize RustcEncodable & RustcDecodable, remove from prelude in next edition #116016
• Add migration lint for Future (based on the previous migration lints)
  • Add migration lint for 2024 prelude additions #125889
• N/A Add migration lint for RustcEncodable
  • This would be nice to have but not required.
• Add documentation to the edition guide.
  • Add 2024 prelude edition-guide#292
  • Document RustcEncodable/RustcDecodable edition-guide#298
• Update edition guide docs with migration details.
  • Add documentation for 2024 prelude migration. edition-guide#314
• Ensure ready for Rust 2024 stabilization.

Related

• Can't ignore soft destabilization of rustc-serialize with #![allow(soft_unstable)] #123156

Implementation History

• Soft-destabilize RustcEncodable & RustcDecodable, remove from prelude in next edition #116016
• Add Future and IntoFuture to the 2024 prelude #121041

Unresolved Questions

• None yet.

cc @jhpratt @Nilstrieb @yoshuawuyts

[Noratrieb]

@rust-lang/project-edition-2024 not sure how and where you want to track this in addition to the issue, but I created the issue to have something to link to.

[ehuss]

Thanks @Nilstrieb. We are doing our tracking in https://hackmd.io/@klAMrLz3QN-4luTZek9cWA/H175lzyea, and I have added that to the list.

Do you know what migration concerns there are with this change? What breakage will it cause, and what is the plan to add a migration lint for that?

[Noratrieb]

When TryFrom/TryInto were added into the prelude in 2021, no migration lint was provided from what I can tell. But I don't see a reason why adding a migration lint wouldn't be possible (though I can't imagine the impact being very large in practice, so it probably doesn't have the highest priority).

[Noratrieb]

Basically the breaking is that the following two programs will now error with a method ambiguity error:

trait Uwu {
    fn poll(&self) {
        println!("uwu");
    }
}
impl<T> Uwu for T {}

fn main() {
    core::pin::pin!(async {}).poll();
}

trait Uwu {
    fn into_future(self) where Self: Sized {
        println!("uwu");
    }
}
impl<T> Uwu for T {}

fn main() {
    async {}.into_future();
}

[ehuss]

rust-2021-prelude-collisions was used to handle the migration for TryFrom/TryInto. I would expect the migration lint would be similar to that.

[Noratrieb]

Ah, I was searching for quite a bit but didn't find it. Then it should be pretty easy to extend the lint pass to also lint for a rust_2024_prelude_collisions.

[traviscross]

We talked through the edition items in the lang call today, and one thing on the list was "Removing Rustc*codable from the prelude" (cc @jhpratt). Let's perhaps track that here also.

[Noratrieb]

I have not gotten to implement the lint yet, but I expect it to be quite simple. If anyone wants to implement, feel free to @rustbot claim and implement it. I do expect to get to it eventually though if no one else does it.

[jhpratt]

I intend on getting to it at some point. I'll claim whenever I start concrete work on it. Until that point, anyone should feel free to do it themself.

[jhpratt]

I am beginning work on the lint for RustcEncodable and RustcDocodable. As a prelude removal rather than addition, it'll likely be different enough that there won't be any overlap in code. As such I will not be working on the other parts of the prelude lint.

[Noratrieb]

I finally got around to implementing the migration lint for future in #125889.

[jhpratt]

As I just said on Zulip, I don't have a ton of time in the near future. If someone else would like to take over my side of the edition lint, please do so!

[traviscross]

@rustbot labels +S-tracking-ready-for-edition

Upon review, with recent work having been merged, this item is now ready for Rust 2024.

Thanks to @Noratrieb and @jhpratt for pushing this work forward, thanks to @ehuss for documentation, and thanks to the various reviewers who helped to get this work landed.