additional-properties

Generates MarshalJSON and UnmarshalJSON methods to allow arbitrary fields when marshaling and unmarshaling structs. See the official JSON Schema definition of additional properties at https://json-schema.org/understanding-json-schema/reference/object.html

This attempts to fix a problem with encoding/json where there's no way to retrieve arbitrary fields when unmarshaling to a struct as described in https://github.com/golang/go/issues/6213.