Unmarshal into struct with field of type func differs from encoding/json

[Kiraub]

Versions:
go version go1.16.5 windows/amd64
github.com/goccy/go-json v0.7.1

What did I try to do:

Use Unmarshal to decode a JSON string into a struct that has a field of type func.

What did I expect:

Analog to encoding/json the field of type func receives the null value (nil) if the field is not found in the JSON object.

If the field is found and has value other than null return with an error in the format:

json: cannot unmarshal <found type> into Go struct field <struct type>.<field name> of type <func type>

If the field is found and has value null it receives the null value.

What happened instead:

Unmarshal returns an error in the format:

json: cannot unmarshal object into Go value of type <func type>

where object does not necessarily represent the type of the actual found/ not found value.

Example:

package goccyjson_test

import (
	json_ "encoding/json"
	"testing"

	"github.com/goccy/go-json"
)

type withFunc struct {
	Name     string
	SomeFunc func() string
}

var text = []byte(`{"Name": "HelloWorld"}`)

func TestWithFuncUnmarshal(t *testing.T) {
	var e, e_ withFunc
	err := json.Unmarshal(text, &e)
	if err != nil {
		t.Log(err)
	} else {
		t.Logf("%#v", e)
	}
	err_ := json_.Unmarshal(text, &e_)
	if err_ != nil {
		t.Log(err_)
	} else {
		t.Logf("%#v", e_)
	}
	if err != nil && err_ == nil {
		t.Fail()
	} 
}

[Kiraub]

The error is generated inside internal/decoder/compile.go#compile since the switch statement does not handle fields of type reflect.Func

[Kiraub]

Fixed with #257