Custom Ruby / Bundler versions

[Matt-Yorkley]

I had a quick look at getting default.nix to build with arbitrary Ruby versions here: main...Matt-Yorkley:versions

I'm not sure if that's the right way to do it, but it builds and successfully runs the app on the latest Ruby 3.1.1 (which was just released a few days ago). It feels like it should be extracted into a nice module somehow, but I'm not sure what that looks like 😅

To be useful for a range of Rails apps, it'll ultimately need the ability to specify a Ruby dot-version, specify a bundler dot-version, then build / fetch them both, then install all gems through bundix using the exact Ruby and bundler versions.

[jsierles]

Nice, this looks about right. We'll probably want to extract these into a separate repo where we build and upload to a binary cache. I'll open a separate issue to try to outline what I think we can try.

[Matt-Yorkley]

Just a note on some of the details of building Ruby versions (which might be a bit much at this early stage, but could be a consideration later): there's a couple of build flags that are quite popular and might be in demand if the Rails/Nix thing takes off, related to increasing Ruby's performance/speed. The first is the --with-jemalloc flag for switching out the default memory allocator, and the second is the new flag for enabling YJIT (which is now available in Ruby, but I think still disabled by default).

[jsierles]

Yeah, I was thinking about that. We definitely want jemalloc enabled for every version, so we should start thinking about it. @samueldr can probably get us into shape here once the build stuff is sorted. I'm going to create a repo for the nix stuff to be extracted to. We can start plopping things like this in there.

[Matt-Yorkley]

There are some bits built in to the pkgs.ruby implementation for handling jemalloc already 👌 But yeah the opt-in or opt-out YJIT thing will be in demand and that makes things a bit more complex if you want to offer that.

[jsierles]

Now this is being moved into https://github.com/fly-apps/nix-base, we can open more specific tickets there.