Support for Jekyll 4.0

[garrett]

Jekyll 4.0 was released last August.

https://jekyllrb.com/news/2019/08/20/jekyll-4-0-0-released/

GitHub Pages hasn't been updated to support (or make it the default) yet.

There are breaking changes which will affect our website. We shouldn't update to the latest GitHub Pages gem (once it exists — it currently still is on 3.x) until porting has been done.

Most of the update will probably be fine. The big breaking change for us would be the new relative_url and removal of the need for site.baseurl.:

The link and post_url tags no longer need site.baseurl prepended every time they’re used. Those tags now use our relative_url filter to take care of this for you. Existing uses of the prepending pattern will break though! Sorry!

(I have some workarounds in place to handle it transparently in some cases. But those should thankfully not be needed. These workarounds and some additional calls to site.baseurl need to be removed or adapted.)

[garrett]

As long as we don't update the Gemfile and Gemfile.lock to have Jekyll >= 4.0.0, when GitHub Pages finally updates, we should be fine.

[garrett]

Also, Pygments has been removed, which may affect source code rendering on our site, unless GitHub Pages keeps support for it (and we may then need to include it in our Gemfile, depending on how they handle it).

[garrett]

Update: No update.

GitHub is still silently dragging their feet on updating Jekyll.

Since we do benefit from the fork and preview method, we shouldn't manually update to 4.0 with actions, but still rely on GitHub Pages for ease of use. (The new version would be nice and we'd definitely benfit from some of the newer features, but there's nothing that we need from it... so it's not urgent. Whenever GitHub finally updates, we'll update.)