tl;dr: I am going to break your workflow and your wiki. Skip to the last section and read on.
== Background ==
As you know, I've been working on a GSoC project to better separate skins and core MediaWiki [1]. Moving Vector and MonoBook to separate repositories is the final step of it, and it's exactly as scary as it sounds.
Until recently MediaWiki was heavily interconnected with the core skins, particularly Vector – right now it is only slightly interconnected and I have some patches pending to make it not so at all [2].
[1] https://www.mediawiki.org/wiki/Separating_skins_from_core_MediaWiki [2] https://gerrit.wikimedia.org/r/#/q/topic:skinning,n,z
== The plan ==
* Fix up some remaining issues with Vector being required (I have already fixed most) * Stop always loading MonoBook and Vector [patch pending: https://gerrit.wikimedia.org/r/148509 + dependencies] * Use a special fallback when no skins are installed [patch pending: https://gerrit.wikimedia.org/r/148508] * Move MonoBook and Vector to separate repositories * Ship MonoBook, Vector and some more skins with the installer tarball * Enable them during the installation [patch merged: https://gerrit.wikimedia.org/r/138652]
== What it means for you ==
If you're upgrading a wiki or you're a developer working on master, THIS IS A BACKWARDS INCOMPATIBLE CHANGE. Your wiki will continue to work, it will just look ugly (no styles).
When we do this and you upgrade, you're going to get a big helpful message asking you to install and enable some skins and explaining how to do this (see https://gerrit.wikimedia.org/r/148508 for implementation; basically, put the files/repository under skins/ and require_once in LocalSettings).
Try it out with this patch: https://gerrit.wikimedia.org/r/148509
After you do this, you'll be able to switch to slightly older MediaWiki versions without things breaking, as the new skins will work with old MediaWiki (the new directory names are different… unless you're using a case-insensitive OS).
I hope this sounds reasonable to everyone, and I hope to have this done around the time of Wikimania (possibly during it; I'll be there). I don't think there is a less disruptive way to do this, other than not doing it at all; if you come up with one, please share it.