[configoptional] Implement Validate()?

[jmacd]

Component(s)

No response

Describe the issue you're reporting

The existing code base uses reflection to recursively apply Validate() to nested configuration objects.
This breaks when configoptional is used, e.g., for QueueConfig/BatchConfig in exporterhelper, see e.g., this fix: open-telemetry/opentelemetry-collector-contrib#41830
I believe this is possibly something we should address.

Tip

_{React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it. Learn more here.}

[jmacd]

I tried the obvious thing in configoptional, like

func (o Optional[T]) Validate() error {
	if o.HasValue() {
		var v any = (*o.Get())
		if validator := v.(xconfmap.Validator); v != nil {
			return validator.Validate()
		}
	}
	return nil
}

var _ xconfmap.Validator = Optional[int]{}

but it doesn't get called.

[jmacd]

type invalid struct {}

func (invalid) Validate() error {
	return fmt.Errorf("invalid")
}

var _ xconfmap.Validator = invalid{}

type hasNested struct {
	couldBe Optional[invalid]
}

func TestOptionalValidate(t *testing.T) {
	require.NoError(t, xconfmap.Validate(hasNested{
		couldBe: None[invalid](),
	}))
	require.Error(t, xconfmap.Validate(hasNested{
		couldBe: Some[invalid](invalid{}),
	}))
}

[evan-bradley]

@jmacd Thanks for catching this. Since Optional has private fields, as where most config structs are required to have all their fields public, we need it to manually continue the Validate call chain. I've opened a PR that should fix this across for all usages of the type.