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

[Eli Zaretskii]

> From: Jonas Bernoulli <jonas@bernoul.li>
> Cc: 37774@debbugs.gnu.org
> Date: Wed, 06 Nov 2019 17:26:12 +0100
> 
> ------
> (defface testing '((t (:background "LightYellow"))) "DOC")
> 
> (overlay-put (make-overlay (point-min) (point-max) nil t)
>              'face ; or 'font-lock-face
>              'testing)
> 
> (remove-overlays (point-min) (point-max))
> 
> (put-text-property (point-min) (point-max) 'font-lock-face 'testing)
> ------

Thanks.

> I have not yet looked into why Magit's diff faces extend beyond eol even
> though I didn't tell them too

Crystal ball says that Magit faces which inherit from some core faces
behave differently than those which don't inherit.