bug#68214: Completion sorting customization by category

[Daniel Mendler <mail@daniel-mendler.de>]

Juri Linkov <juri@linkov.net> writes:

>>>>> This function could be used to look up the other meta data
>>>>> functions too, `display-sort-function`, `annotation-function`,
>>>>> `affixation-function`, `group-function`, etc.
>>>>
>>>> All these meta data functions could be added later to
>>>> completion-category-overrides after pushing the current patch.
>>>
>>> Makes sense, the `display-sort-function' is a good start. I suggest to
>>> at least add the `cycle-sort-function' too. The cycle threshold can be
>>> customized too.
>>
>> Looks like the cycle threshold is already supported,
>> so I'll add the other meta data.
>
> This looks like a complete patch, but it's not completely tested yet:

If we are going with a solution which supports customizing arbitrary
metadata based on category, we could also adjust
`completion-metadata-get' and avoid the introduction of a separate
function `completion-metadata-override-get'. This will result in a
smaller and simpler code change overall.

(defun completion-metadata-get (metadata prop)
  "Get PROP from completion METADATA.
If the metadata specifies a completion category, the variables
`completion-category-overrides' and
`completion-category-defaults' take precedence."
  (if-let (((not (eq prop 'category)))
           (cat (alist-get 'category metadata))
           (over (completion--category-override cat prop)))
      (cdr over)
    (alist-get prop metadata)))