bug#22324: 25.0.50; completion-category-defaults style doesn't override completion-styles (gets prepended instead)

[Dmitry Gutov <dgutov@yandex.ru>]

On 28.01.2022 18:56, Stefan Monnier wrote:
>> If we were designing it from the ground up, we probably wouldn't add an
>> 'ignore' style. We could have added a special value like 't' which would
>> mean the opposite (*do* the fallback, for those users who would want their
>> configs to be just a little bit more terse),
> 
> FWIW, the choice of using a fallback to `completion-style` was made for
> `completion-category-defaults` so that those package-choices don't
> unilaterally override the user's choice in `completion-style`.
> 
> For `completion-category-override` there is indeed not much need for
> a fallback, since it's set by the same person as `completion-style`.

That seems to argue for Daniel's original suggestion: to make 
'-overrides' a "real" override and keep the composition behavior for the 
'-defaults' variable.

Trying to honor the user's customization of 'completion-styles' makes a 
certain amount of sense. Though I don't know how much we honor it this 
way: if the user is relatively new, they might not even know to keep 
typing to see the fallback, after noting that their input does not give 
them the matches they expected.

It's more of a critique of the whole "list of styles" design, admittedly.