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Tracking Issue for const str::split_at* #131518

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zachs18 opened this issue Oct 10, 2024 · 0 comments · Fixed by #134016
Closed
1 of 4 tasks

Tracking Issue for const str::split_at* #131518

zachs18 opened this issue Oct 10, 2024 · 0 comments · Fixed by #134016
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C-tracking-issue Category: An issue tracking the progress of sth. like the implementation of an RFC T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@zachs18
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zachs18 commented Oct 10, 2024 •
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Feature gate: #![feature(const_str_split_at)]

This is a tracking issue for using str::split_at, str::split_at_mut, str::split_at_checked, str::split_at_mut_checked in const, which allows dividing one (mutable) string slice into two (fallibly) at an index during const-eval.

Public API

// core::str
impl str {
    pub const fn split_at(&self, mid: usize) -> (&str, &str);
    pub const fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str);
    pub const fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>;
    pub const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut str, &mut str)>;
}

Steps / History

Unresolved Questions

  • None yet.

Footnotes

  1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩
@zachs18 zachs18 added C-tracking-issue Category: An issue tracking the progress of sth. like the implementation of an RFC T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Oct 10, 2024
This was referenced Oct 10, 2024
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workingjubilee added a commit to workingjubilee/rustc that referenced this issue Oct 29, 2024
@workingjubilee
Rollup merge of rust-lang#131520 - zachs18:const-str-split, r=Noratrieb
b496974 
Mark `str::is_char_boundary` and `str::split_at*` unstably `const`.

Tracking issues: rust-lang#131516, rust-lang#131518

First commit implements `const_is_char_boundary`, second commit implements `const_str_split_at` (which depends on `const_is_char_boundary`)

~~I used `const_eval_select` for `is_char_boundary` since there is a comment about optimizations that would theoretically not happen with the simple `const`-compatible version (since `slice::get` is not `const`ifiable) cc rust-lang#84751. I have not checked if this code difference is still required for the optimization, so it might not be worth the code complication, but 🤷.~~

This changes `str::split_at_checked` to use a new private helper function `split_at_unchecked` (copied from `split_at_mut_unchecked`) that does pointer stuff instead of `get_unchecked`, since that is not currently `const`ifiable due to using the `SliceIndex` trait.
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Oct 29, 2024
@rust-timer
Unrolled build for rust-lang#131520
5b1c381 
Rollup merge of rust-lang#131520 - zachs18:const-str-split, r=Noratrieb

Mark `str::is_char_boundary` and `str::split_at*` unstably `const`.

Tracking issues: rust-lang#131516, rust-lang#131518

First commit implements `const_is_char_boundary`, second commit implements `const_str_split_at` (which depends on `const_is_char_boundary`)

~~I used `const_eval_select` for `is_char_boundary` since there is a comment about optimizations that would theoretically not happen with the simple `const`-compatible version (since `slice::get` is not `const`ifiable) cc rust-lang#84751. I have not checked if this code difference is still required for the optimization, so it might not be worth the code complication, but 🤷.~~

This changes `str::split_at_checked` to use a new private helper function `split_at_unchecked` (copied from `split_at_mut_unchecked`) that does pointer stuff instead of `get_unchecked`, since that is not currently `const`ifiable due to using the `SliceIndex` trait.
@zachs18 zachs18 mentioned this issue Dec 7, 2024
Merged
jhpratt added a commit to jhpratt/rust that referenced this issue Feb 14, 2025
@jhpratt
Rollup merge of rust-lang#134016 - zachs18:stable-const-str-split_at,…
8b88b2e 
… r=Amanieu

Stabilize `const_is_char_boundary` and `const_str_split_at`.

Tracking issues: rust-lang#131516, rust-lang#131518

Stabilized const API:

```rs
// in `core`
impl str {
    // const_is_char_boundary feature
    const fn is_char_boundary(&self, index: usize) -> bool;

    // const_str_split_at feature, depends on const_is_char_boundary
    const fn split_at(&self, mid: usize) -> (&str, &str);
    const fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str);
    const fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>;
    const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut str, &mut str)>;
}
```

This will allow safely splitting string slices during const-eval.

Closes rust-lang#131516, Closes rust-lang#131518

This will need FCP.
r? libs-api

IIUC these do not use any new const language features (i.e. they are implementable manually on stable 1.83.0 using `unsafe`: [playground link](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3679632cd1041084796241b7ac8edfbd)).

Cc `@rust-lang/wg-const-eval` (I don't know if I have the permissions for this ping; if not, someone else please ping wg-const-eval if it is necessary)
@bors bors closed this as completed in 58e84ff Feb 15, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Feb 15, 2025
@rust-timer
Unrolled build for rust-lang#134016
04eafc4 
Rollup merge of rust-lang#134016 - zachs18:stable-const-str-split_at, r=Amanieu

Stabilize `const_is_char_boundary` and `const_str_split_at`.

Tracking issues: rust-lang#131516, rust-lang#131518

Stabilized const API:

```rs
// in `core`
impl str {
    // const_is_char_boundary feature
    const fn is_char_boundary(&self, index: usize) -> bool;

    // const_str_split_at feature, depends on const_is_char_boundary
    const fn split_at(&self, mid: usize) -> (&str, &str);
    const fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str);
    const fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>;
    const fn split_at_mut_checked(&mut self, mid: usize) -> Option<(&mut str, &mut str)>;
}
```

This will allow safely splitting string slices during const-eval.

Closes rust-lang#131516, Closes rust-lang#131518

This will need FCP.
r? libs-api

IIUC these do not use any new const language features (i.e. they are implementable manually on stable 1.83.0 using `unsafe`: [playground link](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3679632cd1041084796241b7ac8edfbd)).

Cc ``@rust-lang/wg-const-eval`` (I don't know if I have the permissions for this ping; if not, someone else please ping wg-const-eval if it is necessary)
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Stabilize const_is_char_boundary and const_str_split_at. zachs18/rust
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