bug#38563: 27.0.50; Company popup renders with newlines (?) inheriting the bg properties of the character at next line's bol

[Dmitry Gutov]

On 12.12.2019 13:32, Eli Zaretskii wrote:
> The "character at next bol" sounds strange, since the display engine
> has no look-ahead -- it never examines characters on the next line
> while displaying the current line.  But it all starts making sense
> when you recall that Company mode puts its overlay on that next line.
> So the "inherited" face is not on the next line, it is at the position
> where the Company overlay is set.  IOW, it's the "underlying face" for
> the overlay string.

Yeah, OK. Now that you mentioned the 'default' face, I remembered: it's 
used there exactly so that we don't inherit the background from the 
"underlying face".

> Should be fixed now, please test.

It looks fixed in the whitespace-mode example, but not in the other one.

Just call M-x company-complete-common on the "Author:" line in a LogEdit 
buffer to reproduce. (I've tested common d7efe98951).

By the way, I kind of wonder why the fix added more lines than it 
deleted. Before, this feature just worked. Was that simply by accident? 
Or were the changes brought in by :extend major enough?

> Btw, the bug is triggered because Company mode uses a weird '(default)
> face, a list, instead of just 'default.  This is valid, but it wastes
> a slot in the frame's face cache, so perhaps there's a good reason to
> avoid that and simplify '(default) to 'default when you propertize the
> tooltip text.

Ultimately, the reason it's there like that is because 
font-lock-append-text-property coerces all values to lists. We could 
change that and maybe save some memory in the process. It would be an 
(minor) incompatible change, however.