Option to ignore read-only fields (config: false) for ytypes.Unmarshal

[rimpsh]

Hi,
I'm a student and I'm currently experimenting with ygot in a university project.
Within this scenario I work with a generated GoStruct that also includes read-only fields. For my use case, an option to ignore read-only fields while unmarshalling into a GoStruct (e.g., when preparing a gNMI.SetRequest) would be really useful.

I'm aware of the excludeState option for the generator but since I sometimes need read-only fields (e.g., unmarshalling data from a gnmi.GetResponse) and in some cases I do not, this option does not really fit.

One possible solution could be to extend the ytypes.Unmarshal function which allows to ignore read-only fields while unmarshalling. For example like:

type IgnoreReadOnlyFields struct{}

// IsUnmarshalOpt marks IgnoreReadOnlyFields as a valid UnmarshalOpt.
func (*IgnoreReadOnlyFields) IsUnmarshalOpt() {}

I've tested this in a fork and if this is something that ygot would benefit from, then I would also try to add this to the project.

[wenovus]

Hi @rimpsh Thanks for sharing us your fix.

There is currently a workaround for the problem you described, which is to call the function ygot.PruneConfigFalse. I will admit this is not very discoverable by autocomplete tools, and is an issue that we should take a look at.

I think using the workaround might be easier from a user perspective (once we have the discoverability issue fixed).

However, if your change is pretty simple it might be worth the maintenance effort. I'd say feel free to open a PR and reference this issue so we can at least keep your work in the record.