So I enabled a beta feature today that is part of reading web's quarterly goals (read more about read more here if interested [1])
When enabled it showed up in desktop beta features (yey) but the JavaScript module wasn't loading...
Investigating I discovered that BetaFeatures::isEnabled consults a config variable called wgBetaFeaturesWhitelist
This makes the feature return false if the feature is not in wgBetaFeaturesWhitelist
Apparently however you make the feature show up in the GetBetaFeaturePreferences hook - so the whitelist doesn't actually apply to things we show to users (which I would say would be more important...) [2]
The whitelist also asks when enabling to check with James Forrester and Greg and to note a date 6 months after the last major change. According to these comments all the listed beta features have passed their expiry dates.
Will they live here forever - or is it time to talk about beta features?
[1] https://www.mediawiki.org/wiki/Reading/Web/Projects/Read_more [1] https://phabricator.wikimedia.org/T121182