items.static.const conflicts with actual behavior in stable Rust

[obi1kenobi]

items.static.const says:

Constants cannot refer to statics.

Yet the following works fine: playground

pub const A: i64 = 0;

pub static B: i64 = A + 1;

pub const C: i64 = B + 1;

This may have changed as a result of recent changes related to Rust-for-Linux such as the stabilization of const_refs_to_static: rust-lang/rust#119618

Depending on what the new rule is, there may also be a SemVer hazard here. For example, if the new rule is "consts may only refer to statics without interior mutability" then newly adding interior mutability to a pub static would appear to be a major breaking change. If so, we should consider updating the cargo SemVer reference as well.

[obi1kenobi]

It appears this behavior is new as of Rust 1.83, and is the case when there's no interior mutability in the static: https://blog.rust-lang.org/2024/11/28/Rust-1.83.0.html#new-const-capabilities

[ehuss]

I believe this has already been resolved by #1610.

[obi1kenobi]

Ah you are absolutely right, my bad! I was under the mistaken impression that the deployed reference matches the state of the repo.

Btw, there seem to be two new (to me, at least) SemVer hazards here that I don't believe are mentioned in the cargo SemVer reference:

• a pub static becoming internally mutable
• a pub static becoming extern

In both cases, assignments of the pub static to a downstream const will break, if my reasoning is accurate. If you think this is worth opening a cargo reference issue for, I'd be happy to open one.

[ehuss]

deployed reference matches the state of the repo.

It follows the Rust release process. Master goes to https://doc.rust-lang.org/nightly/reference/ every two weeks, then it goes to https://doc.rust-lang.org/beta/reference/ after 6 weeks, then https://doc.rust-lang.org/stable/reference/ after another 6 weeks.

worth opening a cargo reference issue

Yea, those do seem like things to be cautious of. Feel free to open a new issue at the cargo repo. Thanks!

[obi1kenobi]

Thank you for your patience and guidance, I appreciate it!