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

[Dmitry Gutov <dgutov@yandex.ru>]

On 13.12.2019 10:22, Eli Zaretskii wrote:

>> 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).
> 
> That's not a bug: the face on that thin line on whose first character
> you put the tooltip overlay has a non-nil :extend attribute, so
> Company will have to explicitly say ':extend nil' in its face(s) to
> countermand that.  Recall that a string from a display property merges
> into its face all the attributes from the "underlying" face, so with
> the current :extend machinery it is no longer enough just to specify a
> background color in the display string's face, as you did before.

I see. But isn't the issue that the background from the underlying face 
is used at all, rather that it's extended?

But I suppose I could add a face with ':extend nil' and use it in place 
of 'default' there.

> Btw, if you used 'default instead of '(default), I think that would
> have avoided the issue as well, because the default face gets a
> special treatment in this context.

I can bump the requirement to Emacs 24.4 and use add-face-text-property 
there (too bad for setting mouse-face only the slower function is 
available), but as you noted in the follow-up email, it doesn't help 
with the remaining example.

>> By the way, I kind of wonder why the fix added more lines than it
>> deleted.
> 
> ??? I added a condition under which not to merge a face, so how can I
> avoid adding a few lines?  The addition is 7 lines of code, including
> a small refactoring, all the rest is comments.

If the issue is "whether to extend", then indeed, it makes sense, thanks.

>> Before, this feature just worked. Was that simply by accident?
>> Or were the changes brought in by :extend major enough?
> 
> Previously, whether a face's background was extended to EOL was
> determined only by the background color of the newline; now the
> :extend attribute determines that independently of the background
> color.

...but the background color is taken specifically from the face that 
specified :extend?