`assert_eq!` fails with `const { .. }` in Rust 2024

[traviscross]

This code fails to compile in Rust 2024 when it should pass:

//@ edition:2024
fn main() {
    assert_eq!(0, const { 0 });
    //~^ ERROR no rules expected keyword `const`
}

This will be fixed, I expect, by migrating the standard library to Rust 2024, and when doing that, by using the :expr rather than :expr_2021 macro fragment specifier in assert_eq and similar macros.

cc @rust-lang/wg-macros @compiler-errors @ehuss

[compiler-errors]

Yeah, this will begin working as soon as the standard library is upgraded to 2024. I don't think there's anything actionable to do here.

[tgross35]

Maybe this could go in tests/crashes (without the //~) so it gets noted once that upgrade happens and it starts passing? Not sure if tests/crashes is only crashes or just a more general xfail.

[compiler-errors]

Crashes is for ICEs only

[traviscross]

It could go in as a known-bug UI test I would expect.

[ehuss]

I think this is mostly a duplicate of #126459. No standard library macros with expr will work with bare const{} until the standard library is updated (regardless of the calling crate's edition). This isn't specific to assert_eq. The same goes for any user crates which have exported macros.