Create a Cloud Native Buildpack for OCaml

[jchavarri]

https://buildpacks.io/docs/buildpack-author-guide/create-buildpack/

Cloud Native Buildpack (CNB) would allow to have much faster times between builds in Heroku deployments, as there's no need to rebuild all images from scratch again.

Questions:

• What's the best way to get opam binaries?
• Is it even needed? Or should a builder be added to include also a stack that points to opam2 Docker images?
• Is it ok to cache ~/.opam folder for caching between builds?
• What's the analog of Gemfile.lock in opam?
• How to handle cache restoring? In this example with Ruby bundler it seems they pass the cache layer through a command line arg, but that's not possible with opam. Is it possible with cloud native builds to take the layer folder and put it back in ~/.opam? Or is there an env variable that can be set to tell opam where the .opam folder is?