Custom (Un-)Marshaller on Generic Types ignored

[loeffert]

It looks like go-yaml doesn't support generics very well. Custom (Un-)Marshaller on a struct like MyType isn't called. The only way to get the Data Attribute exported is to make it public.

This is fully ignored:

type MyType[T any] struct {
	data T
}

This is exported, but the implemented MarshalYAML and UnmarshalYAML functions are never called:

https://go.dev/play/p/Fb7yQ-gAQJn

package main

import (
	"fmt"

	"gopkg.in/yaml.v3"
)

type Example struct {
	F int `yaml:"a,omitempty"`
	B int
}

type AnotherExample struct {
	B int
	C MyType[Example]
}

type MyType[T any] struct {
	Data T `yaml:"data"`
}

func (j MyType[T]) MarshalYAML() ([]byte, error) {
	fmt.Println("marshal yaml")
	return yaml.Marshal(j.Data)
}

func (j *MyType[T]) UnmarshalYAML(b []byte) error {
	fmt.Println("unmarshal yaml")
	return yaml.Unmarshal(b, &j.Data)
}

func NewMyType[T any](data T) MyType[T] {
	return MyType[T]{
		Data: data,
	}
}

func main() {
	e := Example{
		F: 1,
		B: 2,
	}
	dataE, err := yaml.Marshal(e)
	if err != nil {
		panic(err)
	}
	fmt.Println(string(dataE))

	ae := AnotherExample{
		B: 3,
		C: NewMyType(e),
	}
	dataAE, err := yaml.Marshal(ae)
	if err != nil {
		panic(err)
	}
	fmt.Println(string(dataAE))
}