Re: BIKESHED: completion faces

[Dmitry Gutov <dgutov@yandex.ru>]

On 04.11.2019 1:30, Stefan Monnier wrote:

> Indeed, part of the issue is the difference between something like
> `basic` and something like `flex`: in `basic` the
> completions-common-part is not terribly interesting, whereas in `flex`
> it's much more so.
> 
> We could use different faces in those two cases, but I feel like it
> would be better if we can find a default that works well in both cases.

I concur.

>> I'm more against using bold for the common part. Underline is
>> less aggravating.
> 
> Hmm... sadly, I find underlying the completions-common-part to be pretty
> awful.  So it looks like both bold and underline are out?
> Should we look for colors (background? foreground?)?

As suggested previously, a light-grey background might work. Or a dark 
foreground.

IOW, either

   (set-face-foreground 'completions-common-part "blue3")

or

   (set-face-background 'completions-common-part "white smoke")

But neither seems optimal for prefix completion still.

Some other ideas:

- No nothing, on the reasoning that 'flex' is not in 'completion-styles' 
by default. And many users who would add it there would probably use it 
exclusively, and could thus customize their completions-common-part face 
to be more informative, to their satisfaction. This suggestion could be 
in the docs somewhere, maybe in the NEWS section that introduces 'flex'.

- Define a new face that would be applied by callers of 
completion-all-completions to those completions where the equation 
"common part == the whole part of the string before the char highlighted 
by first-difference" doesn't hold true. So all uses of this face would 
be informative. Although some absences of it might stand out (where a 
flex match is a strict-prefix one). That face would have a distinct 
background or foreground.

>>>       M-x dovi C-b C-b ?
>>> you'll see that `completions-first-difference` is applied to the "c"
>>> of the "doc-view..." commands because that's the first character after
>>> the position in the candidate that corresponds to the position of
>>> point in the pattern.
>>
>> I'm having trouble reproducing this. Should I be using icomplete-mode?
> 
> No, just `emacs -Q` and then `M-x dovi C-b C-b ?`

OK, thank you. I see it now. Normally one would press TAB, not '?', though.