Should I fill a bug report?

[thmxv]

use bevy::prelude::*;

fn test<T>(_items: &[T])
where
    for<'a> &'a T: IntoIterator<Item = &'a isize>,
{
}

pub fn system() {
    let items = vec![[1,2]];
    test(&items);
}

Causes and error:

error[E0275]: overflow evaluating the requirement `&_: IntoIterator`

at line 11:

test(&items);

Removing the use statement make everything compile fine.

I found some related bug reports for the rust compiler but all are "resolved" (some last month) but I do get this error even if using the nightly toolchain.

Is the code OK? Should I fill a bug report? If yes, for bevy or for the rust compiler?

[MrGVSV]

Yeah a bug report would be nice. It might also help if you could narrow it down to a certain module or trait in the prelude that's causing this.

[thmxv]

Hi,

Thank you.

Should I report the issue for Bevy of for Rust?

Depending on the code to reproduce this issue (I modified it a lot to minimize the code), the type causing this in the prelude is: Res or Local or Mut. For the moment I have Res:

note: required for `&Res<'_, _>` to implement `IntoIterator`

[akimakinai]

The problem reproduces with the following code.

pub struct Local<'s, T>(&'s T);

impl<'s, 'a, T> IntoIterator for &'a Local<'s, T> where &'a T: IntoIterator {
    type Item = <&'a T as IntoIterator>::Item;
    type IntoIter = <&'a T as IntoIterator>::IntoIter;
    fn into_iter(self) -> Self::IntoIter {
        todo!()
    }
}

fn test<T>(_items: &[T])
where
    for<'a> &'a T: IntoIterator<Item = &'a isize>,
{
}

pub fn system() {
    let items = vec![[1,2]];
    test(&items);
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=cac861a1305e1f5520ea1fadb3fd013c

This code compiles fine with -Znext-solver, so it may be a limitation of the current trait solver.

https://rust.godbolt.org/z/9fexfr4K9

[thmxv]

Great, thank you.

So this issue is not related to Bevy but the rust compiler and I suppose they are aware of it there too and I should not fill a bug report for the compiler neither.

Also thank you for the -Znext-solver workaround hopefully this is mature enough so that it will compile my project and dependencies.

[akimakinai]

Yes, it is a compiler issue. There are already many issues with "overflow evaluating the requirement" error, and some seem to be almost identical to this, e.g. rust-lang/rust#106512, but I'm no expert.

[thmxv]

Ok, great. Thanks.

For those who wants to know: The -Znext-solver workaround does not work for a "real life" project:

• It required nightly which might be unstable
• The -Znext-solver option cannot be passed trough cargo rustc which would only use it for the base project but not for the dependencies
• Passing -Znext-solver to the compilation of all the dependencies does not work and cause errors while building some dependencies (in my case bevy_utils)

[thmxv]

I tried changing the "use" statement:
use bevy; causes the issue also
use std::sync::Mutex; or anything std does not causes the issue
use a_non_bevy_module; does not causes the issue