Re: VOTE: Changing completions-common-part face's default

[Dmitry Gutov <dgutov@yandex.ru>]

On 07.11.2019 12:27, João Távora wrote:

>> I recognize others feel differently, though.
> 
> It seems to be more than "feeling".  Have you asked yourself why the
> whole industry seems to does it differently (i.e. with bold or some
> other contrasting color)?

I'm assuming that's rhetorical. But I have also pointed out how we 
differ from "the whole industry" in other respects, for good or bad.

But there are two questions here: do we highlight common-part by default 
at all, and which color to use.

> I think it's because not all people have your
> spectacular eyesight and not all of them have such great monitors (or
> use them at a more conservative power setting).

I'm always using mine at 50% brightness at most. But never mind.

>> then I would really suggest we use it instead. But if it's not legible
>> for you, e.g. my monitor is unusually high-contrast or whatever, oh
>> well.
> 
> If the proposal is blue4 than my votes changes to "against".  The
> reasoning is that it is counter-productive.  I imagine a new user
> enabling, say, M-x fido-mode in Emacs 27, and asking himself "If they
> were going to choose face for this, why choose this
> near-indistinguishable, vision-straining thing?".

The idea is that one would really need to find out why a given string is 
among the matches very rarely. Maybe once of twice, and they'll simply 
trust the completion engine after that. And for a one-off task, one 
might as well squint a little.

If the common scenario is different, and we expect that the user will 
look at common-part every time, to figure out what to type next, maybe 
we should discuss why the first-difference face is not enough for that.

> There's no space
> there to answer "oh, you see, some people didn't like highlighting at
> all, mostly in other matching styles you're not going to use, so we
> chose this crappy middle-of-road compromise.  Also we don't care much
> for your old-man's eyesight."

Vice versa, one might ask why we added this in-your-face highlighting 
why simply looks like a solid blue (or aquamarine) column in the 
Completions buffer. And we'll have to answer that, well, there exists a 
recently added non-default completion style where this highlighting is 
really useful.

> João
> 
> PS: If only there was a way to make flex use another highlighting...

BTW, speaking of backward compatibility, some of the changes in face 
placement you proposed would break company-capf's implementation of the 
'match' action.