Tracking Issue for ByteStr/ByteString

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Feature gate: #![feature(bstr)]

This is a tracking issue for the ByteStr/ByteString types, which represent human-readable strings that are usually, but not always, UTF-8. Unlike &str/String, these types permit non-UTF-8 contents, making them suitable for user input, non-native filenames (as Path only supports native filenames), and other applications that need to round-trip whatever data the user provides.

This was approved in ACP https://github.com/rust-lang/libs-team/issues/502 .

Public API

// In core::bstr
#[repr(transparent)]
pub struct ByteStr(pub [u8]);

impl ByteStr {
    pub fn new<B: ?Sized + AsRef<[u8]>>(bytes: &B) -> &Self { ... }
}

impl Debug for ByteStr { ... }
impl Display for ByteStr { ... }
impl Deref for ByteStr { type Target = [u8]; ... }
impl DerefMut for ByteStr { ... }
// Other trait impls from bstr, including From impls

// In alloc::bstr
#[repr(transparent)]
pub struct ByteString(pub Vec<u8>);

impl Debug for ByteString { ... }
impl Display for ByteString { ... }
impl Deref for ByteString { type Target = Vec<u8>; ... }
impl DerefMut for ByteString { ... }
// Other trait impls from bstr, including From impls

Steps / History

• Implementation: #135073
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• Should we call this BStr/BString, or ByteStr/ByteString? The former will be more familiar to users of the bstr crate in the ecosystem. The latter is more explicit, and avoids potential naming conflicts (making it easier to, for instance, add it to the prelude).
• Should the module be called bstr or change to something like byte_str? https://github.com/rust-lang/rust/issues/134915#issuecomment-2906519023
• Should the Display impl use the Unicode replacement character, or do escaping like the Debug impl?
• Add indexing for the new std::range types, or switch to it exclusively

Review implementation PR #135073 and the public API listed in this tracking issue first. The remaining work is to resolve the naming, module, Display, and indexing questions, then complete the final comment period and stabilization PR.