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rustc_const_unstable should check constness #69630

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DutchGhost opened this issue Mar 2, 2020 · 6 comments · Fixed by #86838
Closed

rustc_const_unstable should check constness #69630

DutchGhost opened this issue Mar 2, 2020 · 6 comments · Fixed by #86838
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A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) A-stability Area: `#[stable]`, `#[unstable]` etc. C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@DutchGhost
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The rustc_const_unstable attribute currently does not check whether the function it is applied upon is indeed a const fn. I feel like it should check that.

I recently made the mistake of forgetting to mark the function const: #69617 (comment)

ping @oli-obk

@jonas-schievink jonas-schievink added A-const-fn A-stability Area: `#[stable]`, `#[unstable]` etc. C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 2, 2020
@oli-obk
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oli-obk commented Mar 2, 2020

Oh yea, that's a good idea. Note that this can't be done for intrinsics at this point, so you need to make sure to only check extern "Rust" functions

@DutchGhost
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I'd be happy and try to implement this. However Im not verry familiar with the compiler structure.
As far as I understood, rust_const_unstable isn't realy a macro, but more an attribute used by the compiler. With some help on where to start, I'd like to give this a try!

@oli-obk
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oli-obk commented Mar 6, 2020

I didn't find a good entry point. I guess you could pass i into

self.annotate(i.hir_id, &i.attrs, i.span, kind, |v| intravisit::walk_item(v, i));
instead of the various i fields and then check i.kind in for https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/enum.ItemKind.html#variant.Fn and check whether it's const (and doesn't have intrinsic Abi). Not sure how messy that gets, but if it's fairly contained, that seems ok to me.

@lambinoo
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lambinoo commented Jul 3, 2021

I am interested in working on this! Could I get assigned to this? I already have a PR for this I think

@LeSeulArtichaut
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@lambinoo You can use the @rustbot claim command

@lambinoo
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lambinoo commented Jul 5, 2021

Oooh, thanks! :D

JohnTitor added a commit to JohnTitor/rust that referenced this issue Jul 7, 2021
…e_check_const, r=oli-obk

Checking that function is const if marked with rustc_const_unstable

Fixes rust-lang#69630

This one is still missing tests to check the behavior but I checked by hand and it seemed to work.
I would not mind some direction for writing those unit tests!
@bors bors closed this as completed in d85718a Jul 8, 2021
@RalfJung RalfJung added the A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) label Dec 1, 2024
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Labels
A-const-eval Area: Constant evaluation, covers all const contexts (static, const fn, ...) A-stability Area: `#[stable]`, `#[unstable]` etc. C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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6 participants