This is a deprecation notice for users of Sweep (the GNU Emacs package for SWI-Prolog) that rely on the sweeprolog-faces-style option to have Sweep mimic the highlighting provided by PceEmacs:
Currently, Sweep provides an option called sweeprolog-faces-style that can be used to have Sweep mimic the highlighting that PceEmacs, the SWI-Prolog built-in editor, applies to Prolog code. That’s mostly intended for making Sweep more familiar for users coming from PceEmacs. The down side is that the implementation of this feature added a layer of complication to the codebase and involved a bespoke and somewhat unconventional setup for controlling code highlighting.
For this reason, the next version of Sweep, version 0.21.0, is going to deprecate sweeprolog-faces-style and include a cleaner way to emulate PceEmacs’s highlighting–a custom theme that you can enable (along other themes that you may be using) to have Sweep code highlighting look like PceEmacs. The theme is called sweeprolog-pce and it will be available with Sweep when you install it from ELPA, the Emacs packages archive (e.g. with M-x package-install RET sweeprolog RET).
In the benefit of unwary users that currently rely on sweeprolog-faces-style, this option is just deprecated but not removed. Moreover, if you have sweeprolog-faces-style set to either light or dark Sweep will detect it when you first open a Prolog buffer and enable the sweeprolog-pce theme for you so everything should continue to work and look as it did. Of course, this behavior is temporary (just for the few coming versions) and shouldn’t be relied upon as a long term solution. Instead, enable the sweeprolog-pce theme directly if you want to.
If you want to help test this change (and Sweep in general) before the release of the next version, you can install Sweep from the development version of ELPA by adding "https://elpa.nongnu.org/nongnu-devel/" to package-archives in your Emacs configuration:
(add-to-list 'package-archives '("nongnu-devel" . "https://elpa.nongnu.org/nongnu-devel/"))
Cheers!