Port #[rustc_legacy_const_generics] to use attribute parser

[Bryntet]

Small PR that ports the #[rustc_legacy_const_generics] to use the new attribute parser!

r? JonathanBrouwer

[rustbot]

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann

[jdonszelmann]

@rusbot author

[Bryntet]

@rusbot author

@jdonszelmann I think you pinged the wrong account earlier

[jdonszelmann]

Make sure to squash these commits later

[jdonszelmann]

r? jdonszelmann
(@JonathanBrouwer feel free to co review, but I already started a bit)

[Bryntet]

I'm having trouble getting ahold of the attributes using the parse_limited like you mentioned

I have the following code that compiles, but it doesn't actually actually work (tests fail because of missing const function arguments)

let Res::Def(DefKind::Fn, def_id) = self.partial_res_map.get(&expr.id)?.full_res()? else {
    return None;
};

// We only support cross-crate argument rewriting. Uses
// within the same crate should be updated to use the new
// const generics style.
if def_id.is_local() {
    return None;
}
if !expr.attrs.is_empty() {
    dbg!(&expr.attrs);
}
let Some(hir::Attribute::Parsed(AttributeKind::RustcLegacyConstGenerics { fn_indexes, .. })) = AttributeParser::parse_limited(tcx.sess, &expr.attrs, sym::rustc_legacy_const_generics, expr.span, expr.id, Some(tcx.features())) else {
    return None;
};

Some(fn_indexes.iter().map(|(num, _)| *num).collect())

I think it's that the expr.attrs is empty, so I tried passing in attrs from compiler/rustc_ast_lowering/src/expr.rs:L105 but that seems to have the same issue

I did a read of the CI results and it does seem like the performance issues are big.

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[jdonszelmann]

@bors rollup

[Zalathar]

Looks like this failed in rollup due to docs relying on a removed import: #150030 (comment)

@bors r-

[bors]

☔ The latest upstream changes (presumably #143924) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[Bryntet]

@rustbot ready

[JonathanBrouwer]

@bors try jobs=dist-x86_64-linux-alt

[rust-bors]

☀️ Try build successful (CI)
Build commit: b3ed8b9 (b3ed8b970963692a6d4c797de8aa321f525e6327, parent: 95a27adcf907bcc1046602c3746dad8cfdf3bf3f)

[JonathanBrouwer]

@bors r=jonathanbrouwer,jdonszelmann

[bors]

📌 Commit 4bd0e65 has been approved by jonathanbrouwer,jdonszelmann

It is now in the queue for this repository.