Some thoughts after converting prometheus-operator resources from YAML to Dhall

[grdryn]

I'm relatively new to Dhall & to this project (thanks for creating it!). I (and I'm sure many others) have existing configs in YAML/JSON/whatever, that I want to switch to being generated by Dhall. I've found @Gabriella439's awesome slide on how that can be done, which uses dhall-kubernetes in the example.

I've managed to put together just enough locally to convert my collection of prometheus-operator PrometheusRule custom resource YAML files to Dhall. I've put the steps that I used at the end below.

I think it would be useful to have that schemas.dhall that I generated be a part of this project, and I've created #26 to get it included if you think it would be useful. There are some things that I'm not 100% sure about though, hence this issue rather than just creating the pull request alone:

1. Would it be useful to structure this project more closely to how the dhall-kubernetes project is structured? E.g. have types/defaults/schemas separated? dhall-kubernetes mentions this dhall-prometheus-operator as the only entry in the "Projects using dhall-kubernetes" section of its README.md; I wonder if there would be benefit if this and any future dhall-*-operator libraries to be layed out in a similar form?
2. Some of the types here are not in schema form ({ Type: Type, default: {}}). Should we look to have those in the same form too? I haven't looked into what would be involved there.

WDYT? If you think either or both of those would be worthwhile, I can try to find some time to look into them.

---

Converting a PrometheusRule YAML file to Dhall

1. Use yaml-to-dhall to generate the corresponding Dhall:

yaml-to-dhall '(https://raw.githubusercontent.com/coralogix/dhall-prometheus-operator/v8.0.0/package.dhall sha256:ebc5f0c5f57d410412c2b7cbb64d0883be648eafc094f0c3e10dba4e6bd46ed4).v1.PrometheusRule.Type' --file ./prometheus/prometheus-rules-developer.yaml --output ./prometheus-rules-developer.dhall

2. Make a schemas.dhall file for this project, to be able to use with dhall rewrite-with-schemas to clean up the Dhall that was generated in step 1 above.

3. Rewrite the Dhall with schemas, using a schemas record of a merge of the dhall-kubernetes schemas (pretty much just for ObjectMeta) with the schemas.dhall, using // because of a collision that I don't care about (Error: Field collision on: Probe.Type):

dhall rewrite-with-schemas --schemas 'https://raw.githubusercontent.com/dhall-lang/dhall-kubernetes/v6.0.0/schemas.dhall // /path/to/local/dhall-prometheus-operator-schemas.dhall' --inplace ./prometheus-rules-developer.dhall

4. Manually tidy up a couple of remaining things:

• replace the schemas import with separate imports for dhall-kubernetes and dhall-prometheus-operator
• replace instances of < Int : Integer | String : Text > with Kubernetes.IntOrString (there is no "schema" for this union, so it doesn't get automatically done)