Wrong uppercase for `ß`

[vbrandl]

I tried this code:

println!("{}", 'ß'.to_uppercase());

I expected to see this happen:

I expected this to print ẞ (see Capital ẞ).

Instead, this happened:

The code printed SS which is often use to represent ß in uppercase.

Since there is a dedicated character for the capital ẞ (which looks really similar to the lowercase ß in this font), I think to_uppercase should return the actual uppercase letter instead of SS.

Meta

rustc --version --verbose:

rustc 1.48.0 (7eac88abb 2020-11-16)
binary: rustc
commit-hash: 7eac88abb2e57e752f3302f02be5f3ce3d7adfb4
commit-date: 2020-11-16
host: x86_64-unknown-linux-gnu
release: 1.48.0
LLVM version: 11.0

rustc +nightly --version --verbose:

rustc 1.50.0-nightly (1c389ffef 2020-11-24)
binary: rustc
commit-hash: 1c389ffeff814726dec325f0f2b0c99107df2673
commit-date: 2020-11-24
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

[lcnr]

i.e. variants STRASSE vs. STRAẞE would be accepted as equally valid

(quickly scraped from https://en.wikipedia.org/wiki/%C3%9F#Capital_form)

I have never seen ẞ, even though I live in germany, and am not sure if changing this is preferable right now as the generally used capitalization is still SS from what I can tell.

[vbrandl]

While both are valid and the former one is used more often (actually I've never seen a capital ẞ in use and I'm from Germany, too), ẞ is the correct uppercase letter for ß...

[nikic]

Rust follows case mapping rules specified by Unicode, which specs that ß must map to SS under default SpecialCasing rules.

[bjorn3]

This has been the case since #26039

[RalfJung]

Rust follows case mapping rules specified by Unicode, which specs that ß must map to SS under default SpecialCasing rules.

So, given this -- is there even a bug here? One might consider this a Unicode bug, but even that is not clear, and Rust seems to be working as intended by matching what Unicode specifies.

[Alexendoo]

Unicode doesn't consider it a bug - https://www.unicode.org/faq/casemap_charprop.html#11

[RalfJung]

All right, closing as "not a bug" then. Thanks all!