Re: [DISCUSSION] Sorting strings in Org mode vs. system locale

[Max Nikulin <manikulin@gmail.com>]

On 05/05/2024 18:59, Ihor Radchenko wrote:
> Ihor Radchenko writes:
> 
>>> If a user access same files from Linux and macOS then it
>>> may be really annoying to get different order of entries in agenda. For
>>> most of Linux users it is better to use more smart
>>> `string-collate-lessp'. Some care is required to sort entries obtained
>>> from multiple buffers in predictable environment (locale, case
>>> conversion table).
>>
>> I agree. We can introduce a new customization -
>> `org-string-sort-function' that will be used across Org mode to sort
>> user text.
> 
> See the attached tentative patch.
> I added a customization, made everything in Org obey it, and provided
> some default options for MacOS users.

Contrary to Eli, I still think that there are enough locales where 
completely disregarding IGNORE-CASE is worse than fallback to `downcase' 
when IGNORE-CASE is t. Perhaps some kind of normalization (NFD?) may 
improve results further.

I consider the following as a kind of graceful degradation

(defun org-sort-function-fallback-downcase
    (a b &optional LOCALE IGNORE-CASE)
  (if ignore-case
     (string-collate-lessp (downcase a) (downcase b) locale ignore-case)
   (string-collate-lessp a b locale ignore-case)))

(defcustom org-sort-function
  (if (string-collate-lessp "a" "B" "C" t)
     #'string-collate-lessp
   #'org-sort-function-fallback-downcase))

I would consider a setter function for `org-sort-function' to avoid 
branches based of `func-arity' in `org-string<'.

I see a little point in purely downcase comparator 
`org-sort-function-downcase'.