Unicode 17?

[ajvondrak]

Unicode 17.0.0 has been out since 2025 September 9: https://www.unicode.org/versions/Unicode17.0.0/

Rust updated shortly thereafter: rust-lang/rust#146330

But the latest update for regex-syntax seems to be from Unicode 16: 9239e7e

The disagreement causes divergent behavior, for example between char methods and regex character classes: EDIT: bad example, see #1387 (comment) instead.

Bad Example

[package]
name = "repro"
version = "0.1.0"
edition = "2024"

[dependencies]
regex = "1.13.1"

use regex::Regex;

fn main() {
    dbg!(char::UNICODE_VERSION);
    let c = '\u{323B0}';
    dbg!(c.is_alphabetic());
    dbg!(Regex::new(r"[[:alpha:]]").unwrap().is_match(&c.to_string()));
}

$ cargo run
   Compiling repro v0.1.0 (/private/tmp/repro)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.69s
     Running `target/debug/repro`
[src/main.rs:4:5] char::UNICODE_VERSION = (
    17,
    0,
    0,
)
[src/main.rs:6:5] c.is_alphabetic() = true
[src/main.rs:7:5] Regex::new(r"[[:alpha:]]").unwrap().is_match(&c.to_string()) = false

Two separate thoughts:

1. Can we bump to Unicode 17?
2. Could we expose a UNICODE_VERSION constant a la char::UNICODE_VERSION (or as in other crates, like unicode_ident::UNICODE_VERSION, unicode_normalization::UNICODE_VERSION, etc)? This could make it easier for some users to catch such version drift in the future, similar to this code: https://github.com/rust-lang/rust/blob/a04c7a037d59b6dedc9f921e84e391f13a257aa4/compiler/rustc_parse/src/lib.rs#L39-L75

Thanks!

[ajvondrak]

Woops, just realized my example uses [[:alpha:]], which is specifically the ASCII alphabetic range. That was just my attempt to simplify the repro from the actual issue I encountered, where \p{XID_Start} wasn't aligning with unicode_ident::is_xid_start (which uses Unicode 17). Same basic idea though:

[package]
name = "repro"
version = "0.1.0"
edition = "2024"

[dependencies]
regex = "1.13.1"
unicode-ident = "1.0.24"

use unicode_ident::is_xid_start;
use regex::Regex;

fn main() {
    dbg!(unicode_ident::UNICODE_VERSION);
    let c = '\u{323B0}';
    dbg!(is_xid_start(c));
    dbg!(Regex::new(r"\p{XID_Start}").unwrap().is_match(&c.to_string()));
}

$ cargo run
   Compiling repro v0.1.0 (/private/tmp/repro)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.41s
     Running `target/debug/repro`
[src/main.rs:5:5] unicode_ident::UNICODE_VERSION = (
    17,
    0,
    0,
)
[src/main.rs:7:5] is_xid_start(c) = true
[src/main.rs:8:5] Regex::new(r"\p{XID_Start}").unwrap().is_match(&c.to_string()) = false