Elided lifetime changes in rust_2018_idioms lint is very noisy and results in dramatically degraded APIs for Bevy

Problem

With the upcoming release of Rust 2024 edition, we're concerned that rust_2018_idioms will be deny by default.

[Editorial comment (TC): This is not an edition item for Rust 2024, and the edition is not accepting any new items, so we can say definitely that this will not be tied to the release of Rust 2024. See here.]

We investigated what these changes will entail for Bevy in bevyengine/bevy#15916, and the impact is quite severe. Our primary user-facing system and query APIs are littered with meaningless lifetimes.

This is a much worse experience with no upside for us, and Bevy and its entire ecosystem will have to manually allow this lint on every project.

Proposed solution

We would appreciate if the elided lifetimes lint could be split out from the rest of the rust_2018_idioms linting, which we generally liked the effect of.

Ideally this would be off by default as well, to avoid needing to teach new users to turn it off as a critical part of project setup.

Here's an example of some in-production code after this lint was applied:

pub fn update_text2d_layout(
    // Text items which should be reprocessed again, generally when the font hasn't loaded yet.
    mut queue: Local<'_, HashSet<Entity>>,
    mut textures: ResMut<'_, Assets<Image>>,
    fonts: Res<'_, Assets<Font>>,
    windows: Query<'_, '_, &Window, With<PrimaryWindow>>,
    mut scale_factor_changed: EventReader<'_, '_, WindowScaleFactorChanged>,
    mut texture_atlases: ResMut<'_, Assets<TextureAtlasLayout>>,
    mut font_atlas_sets: ResMut<'_, FontAtlasSets>,
    mut text_pipeline: ResMut<'_, TextPipeline>,
    mut text_query: Query<'_, '_, (
        Entity,
        Ref<'_, TextLayout>,
        Ref<'_, TextBounds>,
        &mut TextLayoutInfo,
        &mut ComputedTextBlock,
    )>,
    mut text_reader: Text2dReader<'_, '_>,
    mut font_system: ResMut<'_, CosmicFontSystem>,
    mut swash_cache: ResMut<'_, SwashCache>,
) {

@rustbot

Since this seems to have potential non-minimal ecosystem impact, nominating for T-lang discussion.
@rustbot label +I-lang-nominated

Turning this on by default is tracked in #54910 and #91639.

@rustbot

@rustbot labels -A-edition-2024

@alice-i-cecile: If you could, could you please link to what led you to believe this is true?:

With the upcoming release of Rust 2024 edition, rust_2018_idioms will be deny by default.

For reference, this program is currently accepted in nightly Rust 2024:

//@ edition: 2024
//#![deny(rust_2018_idioms)]

struct S<'a>(&'a ());

fn f(x: &()) -> S {
    S(x)
}

fn main() {}

Playground link

There are no open edition items for Rust 2024 that would change this behavior.

This was due to the presence of #54910 in the Lang Edition 2024 project :)

Thanks, that's helpful. It was just an idea. There were a lot of ideas that didn't become actual edition items.

We've passed the go / no go date for all edition items for Rust 2024. The probability of this change happening in a way tied to the release of the Rust 2024 edition is now zero.

Will anything change for async functions: #103470?

Right now, elided lifetimes is a hard error for async functions:

struct Foo<'a> {
    a: &'a String,
}

fn hello(_foo: Foo) {} // no warning

async fn hello(_foo: Foo) {} // implicit elided lifetime not allowed here

It feels really confusing for it to be allowed in regular functions, but not async ones.

My take is that it's unlikely to change in the near future.

I have discussion of choices in my pull request (look for "Existing hard errors").

CI fixes for Rust 1.89 (#20462)

Merge 'main' into 'next-gen-scenes' (#43)

@shepmaster

@shepmaster Your PR doesn't mention such a thing. What's the status of this?

What's the status of this?

Assuming that "this" means what is discussed in the comment from a year ago and not the entire issue, then running the code from that comment shows that the error is still present, mirroring my previous comment that it was unlikely to change.

If you mean some other topic, feel free to elaborate!

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Elided lifetime changes in `rust_2018_idioms` lint is very noisy and results in dramatically degraded APIs for Bevy #131725

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Elided lifetime changes in rust_2018_idioms lint is very noisy and results in dramatically degraded APIs for Bevy #131725

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alice-i-cecile commented on Oct 15, 2024

jieyouxu commented on Oct 15, 2024

alice-i-cecile commented on Oct 15, 2024

16 remaining items

traviscross commented on Oct 16, 2024

alice-i-cecile commented on Oct 16, 2024

traviscross commented on Oct 16, 2024

musjj commented on Nov 6, 2024

shepmaster commented on Nov 6, 2024

theemathas commented on Sep 12, 2025

shepmaster commented on Sep 12, 2025

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Elided lifetime changes in `rust_2018_idioms` lint is very noisy and results in dramatically degraded APIs for Bevy #131725