Re: [PATCH] `completing-read`: Add `group-function` support to completion metadata (REVISED PATCH VERSION 5)

[Juri Linkov]

> 1. By doing such an override the ability of the user to configure the
> completion UI is subverted.

Such an override could be advisable only when the API user provides
an equivalent user option with more choices when necessary.

> 2. Since the variables are let-bound, they influence the behavior of
> nested recursive completion sessions. It is better to override the
> variables with `setq-local` in a `minibuffer-setup-hook`.

Agreed.

> +(defcustom completions-group-sort-function #'identity
> +  "Sorting function for the groups.
> +The function takes and returns an alist of groups, where the each
> +element is a pair of a group title string and the candidate strings
> +belonging to the group."
> +  :type 'function
> +  :version "28.1")

As the most useful non-default choice, it could also include a function
to sort alphabetically.