bug#37774: 27.0.50; new :extend attribute broke visuals of all themes and other packages

[Eli Zaretskii]

> From: Michael Heerdegen <michael_heerdegen@web.de>
> Cc: Andrey Orst <andreyorst@gmail.com>,  Ergus <spacibba@aol.com>,
>   37774@debbugs.gnu.org
> Date: Wed, 16 Oct 2019 10:59:51 +0200
> 
> At least with Helm, Magit and Ediff higlighting often looks very
> unfamiliar.  I guess very often the original purpose had been to
> highlight full visible lines.  Was it intentional to change all of that,
> or only a side effect?

It was intentional, meaning the assumption was that extending the face
past the last character on the line makes little sense in general.
IOW, preventing the extension for most faces was the main point of the
change.