Re: BIKESHED: completion faces

[Stefan Monnier]

>>> bold in completions-first-difference helps to immediately see the
>>> next character to type to narrow completions further.
>> <mild bikeshedding starts>
>> Yes, but some questions, Juri:
>> * wouldn't any other face, say "underline", serve the same purpose?
> underline is less noticeable than bold, when used on a single character
> with completions-first-difference in the "basic" completion style.

I kind of like the underline for first-difference because it is similar
to the underline used in some toolkit's menus to indicate which
key-shortcut to use to select this entry.

>> * In completion styles other than "basic", there are many other
>>   characters, besides the one marked with completions-first-difference,
>>   that you type to narrow completion further, right?
> Other completion styles don't highlight completions-first-difference
> at all.

Apparently it's now the case on `master` but it's a (hopefully
temporary) regression: it definitely worked for `substring` and
`partial-completion` (and I see no reason why it can't work for
`flex` as well) and it makes just as much sense there as for
`basic` completion, if you ask me.

I think it's the `completion-common-part` highlighting which is
influenced by the completion style: its highlighting is much less
important/useful for `basic` completion and than for more complex
completion styles.

> Is it possible to use bold for completions-first-difference only
> in the "basic" completion style, but for other completion styles
> to use bold for completions-common-part?

I don't think we could/should make the faces's aspect depend on the
completion style used.  But the `basic` completion style could use
different faces than `substring`, `flex`, `initials`, and
`partial-completion`, yes.

This said, since the default completion uses sometimes `basic` and
sometimes `partial-completion`, I think it would be odd to have the
*Completions* use different highlighting on a case-by-case basis.


        Stefan