JSON marshalling not working with the `inline` and `omitempty` options

[TheBigLee]

What happened?

When you use a specific field in a resource that has the inline and the omitempty field specified, the json marshaling will fail with the error:

json: cannot marshal Go value of type v1beta1.DataKeySelector: Go struct field
      NamespacedName cannot have any options other than `inline` or `unknown` specified'

This error is for example triggered when using the set field of a release using provider-helm

How can we reproduce it?

• Have a v1beta1.Release from provider-helm
• Have a SetVal object in the release like this:

v1beta1.Release{
  Spec: v1beta1.ReleaseSpec{
    ForProvider: v1beta1.ReleaseParameters{
      ValuesSpec: v1beta1.ValuesSpec{
        Set: []v1beta1.SetVal{
          {
            Name: "password",
            ValueFrom: &v1beta1.ValueFromSource{
              SecretKeyRef: &v1beta1.DataKeySelector{
                NamespacedName: v1beta1.NamespacedName{
                  Namespace: "foo",
                  Name: "bar",
                },
                Key: "password",
              },
            },
          },
        },
      },
    },
  },
}

Why does this fail?
The NamespacedName field in provider-helm has the following json fields: ,inline,omitempty (see: https://github.com/crossplane-contrib/provider-helm/blob/main/apis/release/v1beta1/types.go#L50)
However, this is currently not supported by the json-library used in this function-sdk-go (see: https://github.com/go-json-experiment/json/blob/master/fields.go#L105-L111)

The error is triggered by calling the json.Marshal() function here: https://github.com/crossplane/function-sdk-go/blob/v0.3.0-rc.0/resource/composed/composed.go#L76

What environment did it happen in?

Crossplane version: 1.17
Provider-Helm: v0.19.0
Function-sdk-go: v0.3.0-rc.0
go-json-experiment: v0.0.0-20231102232822-2e55bd4e08b0

[negz]

Hrm, that's unfortunate.

I wonder if this is a behavior change in go-json-experiment relative to when we started using it. The comment I wrote seems to imply that omitempty used to work.

function-sdk-go/resource/composed/composed.go

Lines 63 to 75 in c987192

	// Round-trip the supplied object through JSON to convert it. We use the
	// go-json-experiment package for this because it honors the omitempty field
	// for non-pointer struct fields.
	//
	// At the time of writing many Crossplane structs contain fields that have
	// the omitempty struct tag, but non-pointer struct values. pkg/json does
	// not omit these fields. It instead includes them as empty JSON objects.
	// Crossplane will interpret this as part of a server-side apply fully
	// specified intent and assume the function actually has opinion about the
	// field when it doesn't. We should make these fields pointers, but it's
	// easier and safer in the meantime to work around it here.
	//
	// https://github.com/go-json-experiment/json#behavior-changes

Edit: Ah, I missed that the issue is when inline and omitempty are used together. Is that even a valid combination of tags for encoding/json? I wonder if the inlined (non-struct) fields are actually omitted if they're empty. If they're not omitted, it might be best to update provider-helm.