Modification of extension fields

[woshilapin]

Hi, I'm currently migrating from protobuf:2.27.1 to protobuf:3.0.2.

I'm trying to change the value of a field that is part of an Protobuf extension.

I'm able to access the unknown fields mutably with something like MyMessage.special_fields.mut_unknown_fields() but then I'm trying to use add_varint and I don't know how to provide the number.

In protobuf:2.27.1, I used to be able to do something like my_proto::exts::my_field.field_number but it seems that field_number is now a private field. Is there a new way to do that?

I'm pretty new to Protobuf in general and especially protobuf's crate, so it's possible I missed something.