Valuereflect: Add support for arrays

[alvaroaleman]

Without this, the Extract function generated by applyconfig-gen panics:

unsupported type: [3]int

Fixes #311

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[alvaroaleman]

/assign @liggitt

[liggitt]

Do you have examples of REST APIs using array types (not slice types)? Wouldn't that also error at decode time with incorrect length inputs?

[liggitt]

this special-case doesn't apply to arrays ... json marshals [n]byte as an actual list, not a base-64-encoded string

see https://go.dev/play/p/fG8JTbZSMjR

[liggitt]

I'm not convinced array support in the API is a good idea... making the generator fail on fields of this type might be a better way to move this error earlier to generate time rather than runtime

[alvaroaleman]

Do you have examples of REST APIs using array types (not slice types)? Wouldn't that also error at decode time with incorrect length inputs?

Sorry for taking so long to come back to this. We have a giant sample CRD in controller-tools where ppl add fields that they found problematic over time and we tried to use it for applyconfig generation and currently have a few of these fields commented out: https://github.com/kubernetes-sigs/controller-tools/blob/e0458524f9c6c22915ccfb7b00311ec49410986e/pkg/applyconfiguration/testdata/cronjob/api/v1/cronjob_types.go#L330-L332

The specific case is here: https://github.com/kubernetes-sigs/controller-tools/blob/e0458524f9c6c22915ccfb7b00311ec49410986e/pkg/crd/testdata/cronjob_types.go#L348
This was added in kubernetes-sigs/controller-tools#648 to fix kubernetes-sigs/controller-tools#613

This all predated my involvement in the project and it looks like that PR fixed two issues and all the linked repos ran into the other issue. So no, I don't have an example of a project using fixed-length arrays in their API.

Should we close this and if/when someone complains that their SSA generation doesn't work and its because of this, we can revisit?

[liggitt]

If there's a way to move this from a runtime error to a generate-time error, or from a panic to an error, that seems useful, but that's as far as I would go for now.