Unmarshal and WriteConfigAs work with different tag

[Martzki]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.
• I am not looking for support or already pursued the available support channels without success.
• I have checked the troubleshooting guide for my problem, without success.

Viper Version

1.19.0

Go Version

1.22.5

Config Source

Files

Format

YAML

Repl.it link

No response

Code reproducing the issue

package main

import (
	"fmt"
	"github.com/spf13/viper"
)

type Data struct {
	MemberA string `yaml:"member_a"`
	MemberB string `yaml:"member_b"`
}

func main() {
	// Write
	v := viper.New()
	v.SetConfigType("yaml")
	v.Set("test", Data{MemberA: "a", MemberB: "b"})
	_ = v.WriteConfigAs("1.yaml")

	// Read
	v = viper.New()
	v.SetConfigFile("1.yaml")
	_ = v.ReadInConfig()
	data := make(map[string]Data)
	_ = v.Unmarshal(&data)
	fmt.Println("data from 1.yaml")
	fmt.Println(data)
}

Expected Behavior

The data read from 1.yaml is correct.

Actual Behavior

$ go run viper.go 
data from 1.yaml
map[test:{ }]
$ cat 1.yaml
test:
    member_a: a
    member_b: b

Steps To Reproduce

No response

Additional Information

Unmarshal works with tag mapstructure but WriteConfigAs works with tag yaml when the yaml key is snake case like member_a.
Even the member has both two tags, the problem is still existed:

type Data struct {
        MemberA string `yaml:"member_a" ,mapstructure: "member_a"`
        MemberB string `yaml:"member_b" ,mapstructure: "member_b"`
}

[Martzki]

Wrong tag format, use delimiter will work.

type Data struct {
        MemberA string `yaml:"member_a" mapstructure: "member_a"`
        MemberB string `yaml:"member_b" mapstructure: "member_b"`
}