Re: Updating *Completions* as you type

[Juri Linkov]

>>>> I don't think this is realistic to add an individual option in all cases.
>>>
>>> That's not necessary.  We could also do possibility C that I described
>>> before:
>>>
>>>>> C.
>>>>> - Remove display-sort-function from the metadata
>>>>> - add the 'read-kill category to the metadata
>>>>> - add 'read-kill to completion-category-defaults
>>>>> (diff is 3 lines)
>>>
>>> That seems simple and straightforward.
>>
>> Removing display-sort-function is still less safe
>> than just adding a category.
>
> Why do you say that?
>
> The reason that comes to mind is that there are replacement completion
> UIs which will need to explicitly add support for the category.  So
> removing display-sort-function will affect them immediately, when they
> might not yet have support for getting display-sort-function from
> completion-category-defaults.
>
> That is true.
>
> But that actually suggests a further argument in this direction: if we
> use user options which change the display-sort-function in the table
> metadata, we'll have support for all completion UIs out of the box.
>
> That seems really desirable!  So maybe we do want a solution like A
> where we add a user option?  Since that user option will work for all
> completion UIs.
>
> Announcing "you can now customize the sorting order of a bunch of
> completing-read-based things in this new way" but having that new way
> only work for the default completion UI is a bit sad, although of course
> they can support the new way eventually.

This is what I believe they should do: we add a category,
and they support it as well.

>>> Identity obviously keeps the original order, but what is the original
>>> order?  That is not documented anywhere and I don't think it's
>>> intuitive.  The user can always just try it and see, but that's a poor
>>> substitute for documentation.
>>
>> In these rare cases when the default order is not intuitive,
>> this can be explained in the docstring of the command that uses
>> 'completing-read', e.g. in the docstring of 'read-from-kill-ring'.
>
> Hm, I do think the wording on that would be a bit tricky.  Since
> *actually* the default behavior today is alphabetical sorting.  We would
> want to say "if completions-sort is nil, read-buffer completions are in
> buffer-list order".
>
> I guess it's not too bad, but we also need to document the category
> symbol.  And perhaps the version it was added in.  All together it still
> seems to me that it would be better to just mention
> 'read-from-kill-ring-sort' in the docstring of 'read-from-kill-ring'.

I'm still not convinced that a user option is needed for such minor thing.

>>>> I still don't understand why do you worry about this precedence when
>>>> the user option completion-category-overrides is nil by default.
>>>>
>>>> Could you describe a use cases when such precedence might become a problem?
>>>
>>> If some table needs an individual option (because the sorting needs to
>>> affect the completion generation), but the table shares a category with
>>> other tables, then that individual option will be overridden by the
>>> category configuration.
>>
>> Agreed, this is a problem.
>>
>>> For example, project-prompt-project-name allows one to complete over
>>> project names.  If I wanted to sort its completions by some detail of
>>> the underlying project (how recently the git repo was updated, maybe),
>>> that would require the table to change behavior.  So it would need an
>>> individual option.
>>
>> Or an individual subcategory.
>>
>>> However, project-prompt-project-name uses the same category as
>>> project-find-file.  So if the user configured sorting for
>>> project-find-file, it will override the table-specific option for
>>> project-prompt-project-name.
>>
>> I believe they should use two different subcategories, e.g.
>> 'project-file' and 'project-name'.
>
> I agree, but...
>
>>> I suppose another option is to simply declare that every table has to
>>> have a unique category.  That would make "category" a misnomer though.
>>
>> Even such subcategories as 'project-name' make sense to use in other
>> possible cases when reading a project name.
>
> ...if the project-name category is used for other tables too, but the
> option is supposed to be specific to an individual completion table,
> then we have the same problem again.

And an alternative to add separate options to all these tables
doesn't look more attractive.