Automate pkl class creation from Go types

[KevinGimbel]

Hello! I'd be very interested in auto-generating a pkl Class from a Go type. As far as I can see this isn't possible out of the box, and there's probably reasons.

We'd like to use pkl as a typed layer in working with Kubernetes YAMLs and CRDs, for example we want to use pkl with Crossplane types like https://github.com/crossplane/crossplane/blob/main/apis/apiextensions/v2/xrd_types.go

Is there any way of automating the conversion of the Go types to pkl classes (or similar)? We could also do this by hand and keep track of upstream api changes, but having some sort of automation would be nice(er).

There was some discussion in #230 but I feel like the solution there is not satisfying for what I plan/want.

[HT154]

In the context of Kubernetes specifically, the most straightforward route here is most likely:

1. Generate your Pkl types directly from the CRDs using https://pkl-lang.org/package-docs/pkg.pkl-lang.org/pkl-pantry/k8s.contrib.crd/current/generate/index.html.
2. Render this output to YAML. If you're using pkl-go this is the Evaluator.EvaluateOutputBytes API (which will return a byte buffer containing the encoded YAML text).
3. Use the normal k8s go APIs to unmarshal the YAML into the existing structs.

The "direct" pkl-go evaluation flow relies on having structs (often generated with pkl-gen-go) with pkl field tags, but since it seems like you don't control these structs that's not an option. (There are also some issues around supporting Pkl's Duration and DataSize values the YAML rendering solves by producing the standard k8s string representation)