Support std::char::UNICODE_VERSION

[sugar700]

Values of that constant depend on Rust version:

Rust 1.44: (13, 0, 0)
Rust 1.38 to 1.43: (12, 1, 0)
Rust 1.28 to 1.37: (11, 0, 0)

[jhpratt]

Can you please provide a source? This seems like a trivial addition that I could make this weekend.

[sugar700]

For Rust 1.44, upgrade to Unicode 13.0 was mentioned in changelog: https://github.com/rust-lang/rust/blob/master/RELEASES.md.

For determination whether Unicode version is at least 12, the following program can be executed. U+10FE0 character was added in Unicode 12.0. rust-lang/rust#62641 did update Unicode version from 11.0 to 12.1 (see diff for src/libcore/unicode/tables.rs), so there is no need to concern about 12.0, no version of Rust had 12.0, the update was to 12.1.

fn main() {
    println!("{}", '\u{10FE0}'.is_alphabetic());
}

For determination whether Unicode version is at least 11, the following program can be executed. U+1C90 character was added in Unicode 11.0. The minimum Rust version supported by standback is 1.31, and the Unicode update occured in 1.28, so there is no need to look deeper.

fn main() {
    println!("{}", '\u{1C90}'.is_alphabetic());
}

For list of Unicode versions, https://unicode.org/history/publicationdates.html can be checked. 11.0.0, 12.0.0, 12.1.0 and 13.0.0 were the only Unicode versions that needed to be tested.

[jhpratt]

Status update: I'm quite busy, and intend on doing a joint release for 1.45 and 1.46 support. This would include both this issue and the open PR.