Make slice comparisons const by oli-obk · Pull Request #143925 · rust-lang/rust

oli-obk · 2025-07-14T11:41:40Z

This needed a fix for derive_const, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while const_trait_impl is still unstable.

r? @fee1-dead

cc #143800

rustbot · 2025-07-14T11:41:47Z

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

RalfJung · 2025-07-14T13:14:20Z

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

+
+        let mut attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
+
+        if self.is_const && self.is_staged_api_crate {


There's clearly something interesting going on here, please add a comment explaining what.

I'm fine with this being a temporary solution. To me, we should change #[derive_const(PartialEq)] to something like #[derive(PartialEq(const))] (syntax to-be-bikeshedded), then we can have #[derive(PartialEq(const, unstable))] in all standard library crates.

How does it know which feature gate to use...?
We're fairly close to actually enforcing feature stability on impls (#140399) so this question matters soon, IIUC.

it doesn't. All derived const trait impls are under the derive_const feature gate

RalfJung · 2025-07-14T13:14:56Z

library/core/src/slice/cmp.rs

        // See PR https://github.com/rust-lang/rust/pull/116846
-        for idx in 0..self.len() {
+        let mut idx = 0;
+        while idx < self.len() {


This should get a FIXME(const-hack).

fee1-dead · 2025-07-15T05:53:23Z

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

+
+        let mut attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
+
+        if self.is_const && self.is_staged_api_crate {


I'm fine with this being a temporary solution. To me, we should change #[derive_const(PartialEq)] to something like #[derive(PartialEq(const))] (syntax to-be-bikeshedded), then we can have #[derive(PartialEq(const, unstable))] in all standard library crates.

fee1-dead · 2025-07-15T05:57:50Z

@bors r+ rollup

bors · 2025-07-15T05:57:53Z

📌 Commit 19c2f1b has been approved by fee1-dead

It is now in the queue for this repository.

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ``@fee1-dead`` cc rust-lang#143800

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ```@fee1-dead``` cc rust-lang#143800

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ````@fee1-dead```` cc rust-lang#143800

fee1-dead · 2025-07-15T16:52:33Z

@bors r-

Failed in rollup: #143978 (comment)

Needs a rebase after #143875

Also make it *only* usable on nightly

oli-obk · 2025-07-17T17:58:27Z

@bors r=fee1-dead

bors · 2025-07-17T17:58:30Z

📌 Commit 68b415a has been approved by fee1-dead

It is now in the queue for this repository.

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? `@fee1-dead` cc rust-lang#143800

Rollup of 12 pull requests Successful merges: - #142300 (Disable `tests/run-make/mte-ffi` because no CI runners have MTE extensions enabled) - #143271 (Store the type of each GVN value) - #143280 (Remove duplicate error about raw underscore lifetime) - #143649 (Add test for `default_field_values` and `const_default`) - #143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - #143719 (Emit warning when there is no space between `-o` and arg) - #143833 (Ban projecting into SIMD types [MCP838]) - #143891 (Port `#[coverage]` to the new attribute system) - #143908 (`tests/ui`: A New Order [0/28] ) - #143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - #143925 (Make slice comparisons const) - #143997 (Use $crate in macros for rustc_public (aka stable_mir)) r? `@ghost` `@rustbot` modify labels: rollup

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ``@fee1-dead`` cc rust-lang#143800

Rollup of 12 pull requests Successful merges: - #143280 (Remove duplicate error about raw underscore lifetime) - #143649 (Add test for `default_field_values` and `const_default`) - #143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - #143704 (Be a bit more careful around exotic cycles in in the inliner) - #143908 (`tests/ui`: A New Order [0/28] ) - #143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - #143925 (Make slice comparisons const) - #143997 (Use $crate in macros for rustc_public (aka stable_mir)) - #144013 (resolve: Make disambiguators for underscore bindings module-local) - #144029 (Fix wrong messages from methods with the same name from different traits) - #144063 (Add myself to the `infra-ci` reviewer group and adjust some infra auto-labels) - #144069 (ci: use windows 22 for all free runners) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 11 pull requests Successful merges: - #143280 (Remove duplicate error about raw underscore lifetime) - #143649 (Add test for `default_field_values` and `const_default`) - #143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - #143908 (`tests/ui`: A New Order [0/28] ) - #143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - #143925 (Make slice comparisons const) - #143997 (Use $crate in macros for rustc_public (aka stable_mir)) - #144013 (resolve: Make disambiguators for underscore bindings module-local) - #144029 (Fix wrong messages from methods with the same name from different traits) - #144063 (Add myself to the `infra-ci` reviewer group and adjust some infra auto-labels) - #144069 (ci: use windows 22 for all free runners) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143925 - oli-obk:slice-const-partialeq, r=fee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ```@fee1-dead``` cc #143800

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ```@fee1-dead``` cc rust-lang#143800

…iaskrgr Rollup of 11 pull requests Successful merges: - rust-lang#143280 (Remove duplicate error about raw underscore lifetime) - rust-lang#143649 (Add test for `default_field_values` and `const_default`) - rust-lang#143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - rust-lang#143908 (`tests/ui`: A New Order [0/28] ) - rust-lang#143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - rust-lang#143925 (Make slice comparisons const) - rust-lang#143997 (Use $crate in macros for rustc_public (aka stable_mir)) - rust-lang#144013 (resolve: Make disambiguators for underscore bindings module-local) - rust-lang#144029 (Fix wrong messages from methods with the same name from different traits) - rust-lang#144063 (Add myself to the `infra-ci` reviewer group and adjust some infra auto-labels) - rust-lang#144069 (ci: use windows 22 for all free runners) r? `@ghost` `@rustbot` modify labels: rollup

…ee1-dead Make slice comparisons const This needed a fix for `derive_const`, too, as it wasn't usable in libcore anymore as trait impls need const stability attributes. I think we can't use the same system as normal trait impls while `const_trait_impl` is still unstable. r? ```@fee1-dead``` cc rust-lang#143800

Rollup of 11 pull requests Successful merges: - rust-lang/rust#143280 (Remove duplicate error about raw underscore lifetime) - rust-lang/rust#143649 (Add test for `default_field_values` and `const_default`) - rust-lang/rust#143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - rust-lang/rust#143908 (`tests/ui`: A New Order [0/28] ) - rust-lang/rust#143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - rust-lang/rust#143925 (Make slice comparisons const) - rust-lang/rust#143997 (Use $crate in macros for rustc_public (aka stable_mir)) - rust-lang/rust#144013 (resolve: Make disambiguators for underscore bindings module-local) - rust-lang/rust#144029 (Fix wrong messages from methods with the same name from different traits) - rust-lang/rust#144063 (Add myself to the `infra-ci` reviewer group and adjust some infra auto-labels) - rust-lang/rust#144069 (ci: use windows 22 for all free runners) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 11 pull requests Successful merges: - rust-lang#143280 (Remove duplicate error about raw underscore lifetime) - rust-lang#143649 (Add test for `default_field_values` and `const_default`) - rust-lang#143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - rust-lang#143908 (`tests/ui`: A New Order [0/28] ) - rust-lang#143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - rust-lang#143925 (Make slice comparisons const) - rust-lang#143997 (Use $crate in macros for rustc_public (aka stable_mir)) - rust-lang#144013 (resolve: Make disambiguators for underscore bindings module-local) - rust-lang#144029 (Fix wrong messages from methods with the same name from different traits) - rust-lang#144063 (Add myself to the `infra-ci` reviewer group and adjust some infra auto-labels) - rust-lang#144069 (ci: use windows 22 for all free runners) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 11 pull requests Successful merges: - rust-lang/rust#143280 (Remove duplicate error about raw underscore lifetime) - rust-lang/rust#143649 (Add test for `default_field_values` and `const_default`) - rust-lang/rust#143699 (Make `AsyncDrop` check that it's being implemented on a local ADT) - rust-lang/rust#143908 (`tests/ui`: A New Order [0/28] ) - rust-lang/rust#143909 (docs(alloc::fmt): Make type optional, instead of matching empty string) - rust-lang/rust#143925 (Make slice comparisons const) - rust-lang/rust#143997 (Use $crate in macros for rustc_public (aka stable_mir)) - rust-lang/rust#144013 (resolve: Make disambiguators for underscore bindings module-local) - rust-lang/rust#144029 (Fix wrong messages from methods with the same name from different traits) - rust-lang/rust#144063 (Add myself to the `infra-ci` reviewer group and adjust some infra auto-labels) - rust-lang/rust#144069 (ci: use windows 22 for all free runners) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned fee1-dead Jul 14, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jul 14, 2025

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oli-obk force-pushed the slice-const-partialeq branch from 494d350 to c3b13bb Compare July 14, 2025 12:45

RalfJung reviewed Jul 14, 2025

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oli-obk force-pushed the slice-const-partialeq branch from c3b13bb to 19c2f1b Compare July 14, 2025 15:28

fee1-dead approved these changes Jul 15, 2025

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 15, 2025

samueltardieu mentioned this pull request Jul 15, 2025

Rollup of 12 pull requests #143974

Closed

samueltardieu mentioned this pull request Jul 15, 2025

Rollup of 11 pull requests #143976

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samueltardieu mentioned this pull request Jul 15, 2025

Rollup of 11 pull requests #143978

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bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jul 15, 2025

oli-obk added 4 commits July 17, 2025 15:42

Make Option const PartialEq

2f5722c

Make NonZero const PartialEq

9d29583

Make derive_const usable within libcore again

250648e

Also make it *only* usable on nightly

Make slices [const] PartialEq

68b415a

oli-obk force-pushed the slice-const-partialeq branch from 19c2f1b to 68b415a Compare July 17, 2025 17:58

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 17, 2025

jhpratt mentioned this pull request Jul 18, 2025

Rollup of 12 pull requests #144101

Closed

matthiaskrgr mentioned this pull request Jul 18, 2025

Rollup of 12 pull requests #144110

Closed

matthiaskrgr mentioned this pull request Jul 18, 2025

Rollup of 11 pull requests #144130

Merged

bors merged commit 82fbbdd into rust-lang:master Jul 18, 2025
11 checks passed

rustbot added this to the 1.90.0 milestone Jul 18, 2025


		let mut attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];

		if self.is_const && self.is_staged_api_crate {

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