The SimpleFeed MediaWiki extension is unmaintained and breaks with PHP 7.
Instead of wasting time on riding^Wfixing a dead horse, I decided to replace it with a maintained extension - https://www.mediawiki.org/wiki/Extension:RSS
Note that the "RSS" extension needs a different syntax in the wiki, so we'll have to update all pages that include RSS feeds. Luckily this doesn't affect too many pages - about 30 pages on en.o.o, and probably less on the other wikis. Finding these pages is easy with Special:ReplaceText - search for
<feed in all namespaces and then manually edit the listed pages.
See http://manyboxes.opensuse.org/openSUSE:Planet for an example that already uses the new syntax (and has the old syntax included in the wiki source as comment).
The RSS extension can use templates to vary the layout. By default, it uses MediaWiki:Rss-feed which I adjusted to match the old layout.
The extension allows to specify a whitelist of allowed feeds. Currently I allow everything, but - do we want to restrict that? If so, what should be on the whitelist? (CC'ing Marcus - does the security team want such a restriction?)