Tracking Issue for const checked slice to str conversions

[WaffleLapkin]

Feature gate: #![feature(const_str_from_utf8)]

This is a tracking issue for str::{from_utf8, from_utf8_mut} and str::Utf8Error::{valid_up_to, error_len} as const fn

Public API

// core::str

pub const fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error>;

Public API (stabilized in Rust 1.63)

// core::str

pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error>;

impl Utf8Error {
    pub const fn valid_up_to(&self) -> usize;
    pub const fn error_len(&self) -> Option<usize>;
}

Steps / History

• Implementation: Make slice->str conversion and related functions const #90607
• Final comment period (FCP) (& functions)
• Stabilization PR (& functions)
• Final comment period (FCP) (&mut function)
• Stabilization PR (&mut function)

Unresolved Questions

• None yet.

[Amanieu]

@rfcbot merge

[rfcbot]

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @yaahc

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[WaffleLapkin]

Note that from_utf8_mut is not being stabilized as &mut is still unstable in const context.

cc @oli-obk

[Amanieu]

Tracking issue for &mut in const: #57349

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[mina86]

Could we also get std::ffi::CStr::to_str covered by this issue?

I was hoping this would give me a safe compile-time way to construct str from CStr but currently std::ffi::CStr::to_bytes is not const (for whatever reason) so std::str::from_utf8(cstr_value.to_bytes()) cannot be done in const context.

Alternatively, making std::ffi::CStr::to_bytes const would also work for me.