Json fields with hypen (-) are not decoded properly

[fedulovivan]

Json fields with hypen (-) are not decoded properly (BTW same for original mitchellh/mapstructure).

Minimal reproduction code (tried with go 1.22.5, 1.24)

package main
import (
	"fmt"

	"github.com/go-viper/mapstructure/v2"
)
type Out struct {
	Foo    int `json:"foo"`
	BarBaz int `json:"bar-baz"`
}
func main() {
	in := make(map[string]any)
	in["foo"] = 1
	in["bar-baz"] = 2
	out := new(Out)
	mapstructure.Decode(in, out)
	fmt.Printf("%+v", out)
}

Actual
&{Foo:1 BarBaz:0}
Expected
&{Foo:1 BarBaz:2}

[fedulovivan]

BTW, if I replace mapstructure.Decode with following workaround

func mapstructureDecode(in any, out any) error {
	jsonData, err := json.Marshal(in)
	if err != nil {
		return err
	}
	err = json.Unmarshal(jsonData, out)
	if err != nil {
		return err
	}
	return nil
}

everything works as intended

[ddelpero]

Have you tried mapstructure:"bar-baz" instead of json? I assumed the json tags would also work, but there is an example in the documentation that uses mapstructure.

[fedulovivan]

@ddelpero Thank you, yep I can confirm replacing "json" with "mapstructure" fixes the issue. Anyway this looks like a bug.

[ddelpero]

You can use a custom decoder config:

config := mapstructure.DecoderConfig{
   TagName: "json",
   Result:  &out}

decoder, err := mapstructure.NewDecoder(&config)
if err != nil {
   fmt.Println("Decoder config error: ", err)
}
err = decoder.Decode(in)