bug#42552: 28.0.50; Overlay 'face' property doesn't set the "underlying face" for 'after-string'

[Dmitry Gutov]

I have tried to find a workaround around bug#42521 to render a 
completion popup with images.

The attached patch almost works, except in Emacs 27+ it leads to a
repeat of bug#38563. Meaning, the rendered popup inherits certain
properties (most importantly, :extend) from the character under the end
of the overlay. Leading to similar visual effects, screenshots attached.

I would hope to solve it like we solved it in bug#38563, but the 'face'
overlay property doesn't seem to have any effect here.

The attached patch for company.el should apply cleanly on top of its
current code in ELPA.

The reproduction scenario is almost the same, only in this case the 
problem occurs when the *end* of the overlay falls on a position with
the non-nil 'extend' property (and the overlay is 10 lines long).
See the screenshots.

Please let me know if you need any further clarifications.

I do believe it's a regression, considering the same code works okay in
Emacs 26.3, in exact same situations (whitespace-mode 'tail' face or the
log-edit line under the end of the popup overlay).

In GNU Emacs 28.0.50 (build 25, x86_64-pc-linux-gnu, GTK+ Version 
3.24.20, cairo version 1.16.0)
 of 2020-07-20 built on potemkin
Repository revision: 4c08c2f45b9bb0265f6d7c3529011dee1b18e843
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 20.04.1 LTS

company.el.diff
Description: Text Data

Screenshot from 2020-07-26 20-58-50.png
Description: PNG image

Screenshot from 2020-07-26 20-59-25.png
Description: PNG image