Add contracts for all functions in Alignment

[tautschnig]

Uses the contracts syntax introduced in #128045.

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[jieyouxu]

This needs to be in library/core/src/lib.rs I think

[jieyouxu]

You could also tag contracts-related PRs with F-contracts in the future via

@rustbot label: +F-contracts

in a comment / PR description.

[tgross35]

Could you say some more about the motivation? This feature was merged only a number of hours ago, that seems soon to start using in std. Even once it is more stable, what should and shouldn't get contracts is probably something that needs to get discussed.

@rust-lang/libs any thoughts here?

[jieyouxu]

Yeah, this was only approved as a lang experiment on the lang/compiler side, no idea what the situation is libs side (which certainly should be discussed).

cc @pnkfelix @nikomatsakis @celinval (lang liason and ppl who were implementing this feature compiler side)

[Noratrieb]

I'll libs nominate this for discussion (this should only be discussed after the contracts people mentioned above have replied).

[celinval]

Totally worth discussion, and it would be great to get some feedback on the features that are needed to meet the libs team bar. I am especially curious to see how you think contracts and ub_checks will interact.

[Noratrieb]

It would be useful to know what your plan/intention is with adding contracts here. Is it just to try them out or is annotating the standard library with contracts for downstream consumers part of the goal of contracts?

[tautschnig]

Could you say some more about the motivation? This feature was merged only a number of hours ago, that seems soon to start using in std. Even once it is more stable, what should and shouldn't get contracts is probably something that needs to get discussed.

As far as the motivation is concerned: we're working towards https://rust-lang.github.io/rust-project-goals/2025h1/std-contracts.html, and I created this (draft) PR with the hope to initiate discussion while knowing there is a lot more work to be done on our end.

As I am new contributor: is there other information that I can provide or another forum that I should use rather than this PR?

[tautschnig]

It would be useful to know what your plan/intention is with adding contracts here. Is it just to try them out or is annotating the standard library with contracts for downstream consumers part of the goal of contracts?

Our current goal is https://rust-lang.github.io/rust-project-goals/2025h1/std-contracts.html, though we are in early stages and it indeed is about trying out what works best. Eventually we want to enable verification of downstream consumers, but a lot more work will be required before we get there.

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

   Compiling compiler_builtins v0.1.143
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
   --> library/core/src/ptr/alignment.rs:167:32
    |
167 |     #[cfg_attr(not(bootstrap), contracts::ensures(
    |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
   --> library/core/src/ptr/alignment.rs:134:32
    |
    |
134 |     #[cfg_attr(not(bootstrap), contracts::requires(self.as_usize().is_power_of_two()))]
    |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
   --> library/core/src/ptr/alignment.rs:135:32
    |
    |
135 |     #[cfg_attr(not(bootstrap), contracts::ensures(
    |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
   --> library/core/src/ptr/alignment.rs:107:32
    |
    |
107 |     #[cfg_attr(not(bootstrap), contracts::ensures(
    |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
  --> library/core/src/ptr/alignment.rs:99:32
   |
   |
99 |     #[cfg_attr(not(bootstrap), contracts::ensures(|result| result.is_power_of_two()))]
   |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
  --> library/core/src/ptr/alignment.rs:81:32
   |
   |
81 |     #[cfg_attr(not(bootstrap), contracts::requires(align > 0 && (align & (align - 1)) == 0))]
   |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
  --> library/core/src/ptr/alignment.rs:82:32
   |
   |
82 |     #[cfg_attr(not(bootstrap), contracts::ensures(
   |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
  --> library/core/src/ptr/alignment.rs:59:32
   |
   |
59 |     #[cfg_attr(not(bootstrap), contracts::ensures(
   |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
  --> library/core/src/ptr/alignment.rs:46:32
   |
   |
46 |     #[cfg_attr(not(bootstrap), contracts::requires(mem::align_of::<T>().is_power_of_two()))]
   |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
error[E0433]: failed to resolve: use of unresolved module or unlinked crate `contracts`
  --> library/core/src/ptr/alignment.rs:47:32
   |
   |
47 |     #[cfg_attr(not(bootstrap), contracts::ensures(|result| result.as_usize().is_power_of_two()))]
   |                                ^^^^^^^^^ use of unresolved module or unlinked crate `contracts`
For more information about this error, try `rustc --explain E0433`.
error: could not compile `core` (lib) due to 10 previous errors
Build completed unsuccessfully in 0:05:26
  local time: Wed Feb  5 22:16:10 UTC 2025

[tgross35]

As far as the motivation is concerned: we're working towards https://rust-lang.github.io/rust-project-goals/2025h1/std-contracts.html, and I created this (draft) PR with the hope to initiate discussion while knowing there is a lot more work to be done on our end.

As I am new contributor: is there other information that I can provide or another forum that I should use rather than this PR?

Are there any docs on how contracts work as they exist today? Ignoring the stability question, we need something to refer to about how to use these properly, e.g. in https://doc.rust-lang.org/nightly/unstable-book/. Also, how are contracts that get merged into r-l/rust being verified?

The linked page is somewhat vague about what this means for std. I think we could also use a policy page in the library dev guide (https://std-dev-guide.rust-lang.org) giving guidelines for their use, based on the outcome of any discussion that happens.

Bringing this up on the libs zulip would be a good idea to get the ball rolling https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs.