You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: reader.go
    path of file: ./repos/gluetun/internal/configuration/sources/env
    
    the code of the file until where you have to start completion: package env

import (
	"os"

	"github.com/qdm12/gluetun/internal/configuration/settings"
	"github.com/qdm12/gosettings/sources/env"
)

type Source struct {
	env                 env.Env
	warner              Warner
	handleDepreca
    
func New(warner Warner) *Source {
	handleDeprecatedKey := func(deprecatedKey, newKey string) {
		warner.Warn(
			"You are using the old environment variable " + deprecatedKey +
				", please consider changing it to " + newKey)
	}

	return &Source{
		env:                 *env.New(os.Environ(), handleDeprecatedKey),
		warner:              warner,
		handleDeprecatedKey: handleDeprecatedKey,
	}
}