AutomaticEnv does not override Unmarshaled config slice values

[lwlee2608]

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

1.18.2

Go Version

1.21.1

Config Source

Files

Format

YAML

Repl.it link

No response

Code reproducing the issue

package main

import (
	"strings"
	"testing"

	"github.com/spf13/viper"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

var yamlSimpleSlice = []byte(`
name: Steve
port: 8080
modes:
  - 1
  - 2
  - 3
clients:
  - name: foo
  - name: bar
`)

func TestSliceIndexAutomaticEnv(t *testing.T) {
	v := viper.New()
	v.SetConfigType("yaml")
	r := strings.NewReader(string(yamlSimpleSlice))

	// Read yaml as default value
	err := v.ReadConfig(r)
	require.NoError(t, err)

	assert.Equal(t, "Steve", v.GetString("name"))
	assert.Equal(t, 8080, v.GetInt("port"))
	assert.Equal(t, "foo", v.GetString("clients.0.name"))
	assert.Equal(t, "bar", v.GetString("clients.1.name"))
	assert.Equal(t, []int{1, 2, 3}, v.GetIntSlice("modes"))

	// Override with env variable
	t.Setenv("NAME", "Steven")
	t.Setenv("MODES_2", "300")
	t.Setenv("CLIENTS_1_NAME", "baz")

	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	v.AutomaticEnv()

	// Assert value are overriden
	assert.Equal(t, "Steven", v.GetString("name"))
	assert.Equal(t, 300, v.GetInt("modes.2"))
	assert.Equal(t, "baz", v.GetString("clients.1.name"))

	type ClientConfig struct {
		Name string
	}

	type Configuration struct {
		Port    int
		Name    string
		Modes   []int
		Clients []ClientConfig
	}
	var config Configuration

	// Unmarshal into config struct
	v.Unmarshal(&config)

	assert.Equal(t, "Steven", config.Name) // successfully overridden to 'Steven'
	assert.Equal(t, 8080, config.Port)
	assert.Equal(t, []int{1, 2, 300}, config.Modes) // actual is still default value {1,2,3}
	assert.Equal(t, "foo", config.Clients[0].Name)
	assert.Equal(t, "baz", config.Clients[1].Name) // actual is still default value 'bar'
}

Expected Behavior

Initially read a YAML file with modes set to {1, 2, 3} and clients set to { name: foo, name: bar }.

I expect config.Modes to be []int{1, 2, 300} since the MODES_2 environment variable should override 3 to 300.
Similarly, I expect config.Clients[1].Name value to be overridden by the CLIENTS_1_NAME environment variable from bar to baz.

Actual Behavior

The environment variable did not override the unmarshaled config struct.
config.Modes is still []int{1, 2, 3},
and
config.Clients[1].Name is still bar.

Steps To Reproduce

1.Run above test

Additional Information

The bug only occurs with slice values, i.e., config.Modes and config.Clients[1].Name. Configurations without slices, i.e., config.Name, are still overridden by the env variable.

Note that v.GetInt("modes.2") and v.GetString("clients.1.name") work. Only the unmarshaled struct is bugged.

No response

[github-actions]

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[JckHoe]

Encountering similar issues.

The PR looks good! Would love this feature added.