bug#74155: upcasing strings doesn’t respect standard-case-table

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 01 Nov 2024 13:33:13 +0100
> From:  "Thomas Voss" via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> As of 2017 (I believe), the capital eszett (ẞ) was adopted into the
> German alphabet as the uppercase variable of ß which was previously (and
> which still can be) uppercased to ‘SS’.  Since I prefer to use the newer
> ẞ to the older SS, I have the following line in my configuration:
> 
> 	(set-case-syntax-pair ?ẞ ?ß (standard-case-table))
> 
> When working with characters, this behaves as intended:
> 
> 	(upcase ?ß)
> 	⇒ ?ẞ
> 
> However when working with strings, it doesn’t:
> 
> 	(upcase "ß")
> 	⇒ "SS"
> 
> The same goes for the ‘upcase-word’ and ‘upcase-dwim’ functions which
> still upcase ß to SS.  It seems that whatever code that is handling
> case-conversions for multi-character inputs is not respecting the current
> case table.

This is a feature: characters which have the 'special-uppercase'
property defined for them by the Unicode Standard use their special
upper-case rules that override the case-table.  If you don't want
that, force the special-uppercase property of ß to be nil:

 (upcase "ß")
  => "SS"
 (put-char-code-property ?ß 'special-uppercase nil)
 (upcase "ß")
  => "ẞ"