feat!: accept expand as an option to the env tag (#263)

BREAKING CHANGE: this replaces the `envExpand` tag with the `expand`
option to the `env` tag, to be more consistent with other boolean
options.

closes #262

Signed-off-by: Carlos A Becker <caarlos0@users.noreply.github.com>

README.md

@@ -34,7 +34,7 @@ type config struct {
 	IsProduction bool          `env:"PRODUCTION"`
 	Hosts        []string      `env:"HOSTS" envSeparator:":"`
 	Duration     time.Duration `env:"DURATION"`
-	TempFolder   string        `env:"TEMP_FOLDER" envDefault:"${HOME}/tmp" envExpand:"true"`
+	TempFolder   string        `env:"TEMP_FOLDER,expand" envDefault:"${HOME}/tmp"`
 }
 
 func main() {
@@ -102,10 +102,6 @@ case of absence of it in the environment.
 By default, slice types will split the environment value on `,`; you can change
 this behavior by setting the `envSeparator` tag.
 
-If you set the `envExpand` tag, environment variables (either in `${var}` or
-`$var` format) in the string will be replaced according with the actual value
-of the variable.
-
 ## Custom Parser Funcs
 
 If you have a type that is not supported out of the box by the lib, you are able
@@ -168,6 +164,20 @@ type config struct {
 > value.
 > This also means that custom parser funcs will not be invoked.
 
+## Expand vars
+
+If you set the `expand` option, environment variables (either in `${var}` or
+`$var` format) in the string will be replaced according with the actual value
+of the variable. For example:
+
+```go
+type config struct {
+	SecretKey string `env:"SECRET_KEY,expand"`
+}
+```
+
+This also works with `envDefault`.
+
 ## Not Empty fields
 
 While `required` demands the environment variable to be set, it doesn't check
@@ -214,7 +224,7 @@ import (
 type config struct {
 	Secret       string   `env:"SECRET,file"`
 	Password     string   `env:"PASSWORD,file" envDefault:"/tmp/password"`
-	Certificate  string   `env:"CERTIFICATE,file" envDefault:"${CERTIFICATE_FILE}" envExpand:"true"`
+	Certificate  string   `env:"CERTIFICATE,file,expand" envDefault:"${CERTIFICATE_FILE}"`
 }
 
 func main() {

env.go

@@ -252,6 +252,7 @@ func get(field reflect.StructField, opts Options) (val string, err error) {
 	var loadFile bool
 	var unset bool
 	var notEmpty bool
+	var expand bool
 
 	required := opts.RequiredIfNoDef
 	ownKey, tags := parseKeyForOption(field.Tag.Get(opts.TagName))
@@ -271,14 +272,15 @@ func get(field reflect.StructField, opts Options) (val string, err error) {
 			unset = true
 		case "notEmpty":
 			notEmpty = true
+		case "expand":
+			expand = true
 		default:
 			return "", newNoSupportedTagOptionError(tag)
 		}
 	}
 
 	prefix := opts.Prefix
 	key := prefix + ownKey
-	expand := strings.EqualFold(field.Tag.Get("envExpand"), "true")
 	defaultValue, defExists := field.Tag.Lookup("envDefault")
 	val, exists, isDefault = getOr(key, defaultValue, defExists, opts.Environment)
 

env_test.go

@@ -933,11 +933,11 @@ func TestErrorRequiredNotSetWithDefault(t *testing.T) {
 func TestParseExpandOption(t *testing.T) {
 	type config struct {
 		Host        string `env:"HOST" envDefault:"localhost"`
-		Port        int    `env:"PORT" envDefault:"3000" envExpand:"True"`
-		SecretKey   string `env:"SECRET_KEY" envExpand:"True"`
+		Port        int    `env:"PORT,expand" envDefault:"3000"`
+		SecretKey   string `env:"SECRET_KEY,expand"`
 		ExpandKey   string `env:"EXPAND_KEY"`
-		CompoundKey string `env:"HOST_PORT" envDefault:"${HOST}:${PORT}" envExpand:"True"`
-		Default     string `env:"DEFAULT" envDefault:"def1"  envExpand:"True"`
+		CompoundKey string `env:"HOST_PORT,expand" envDefault:"${HOST}:${PORT}"`
+		Default     string `env:"DEFAULT,expand" envDefault:"def1"`
 	}
 
 	t.Setenv("HOST", "localhost")
@@ -1311,6 +1311,7 @@ func ExampleParse() {
 		Home         string `env:"HOME,required"`
 		Port         int    `env:"PORT" envDefault:"3000"`
 		IsProduction bool   `env:"PRODUCTION"`
+		TempFolder   string `env:"TEMP_FOLDER,expand" envDefault:"${HOME}/.tmp"`
 		Inner        inner
 	}
 	os.Setenv("HOME", "/tmp/fakehome")
@@ -1319,7 +1320,7 @@ func ExampleParse() {
 		fmt.Println("failed:", err)
 	}
 	fmt.Printf("%+v", cfg)
-	// Output: {Home:/tmp/fakehome Port:3000 IsProduction:false Inner:{Foo:foobar}}
+	// Output:  {Home:/tmp/fakehome Port:3000 IsProduction:false TempFolder:/tmp/fakehome/.tmp Inner:{Foo:foobar}}
 }
 
 func ExampleParse_onSet() {
@@ -1495,7 +1496,7 @@ func TestFileBadFile(t *testing.T) {
 
 func TestFileWithDefault(t *testing.T) {
 	type config struct {
-		SecretKey string `env:"SECRET_KEY,file" envDefault:"${FILE}" envExpand:"true"`
+		SecretKey string `env:"SECRET_KEY,file,expand" envDefault:"${FILE}"`
 	}
 
 	dir := t.TempDir()

error.go

@@ -89,7 +89,7 @@ func (e NoParserError) Error() string {
 }
 
 // This error occurs when the given tag is not supported
-// In-built supported tags: "", "file", "required", "unset", "notEmpty", "envDefault", "envExpand", "envSeparator"
+// In-built supported tags: "", "file", "required", "unset", "notEmpty", "expand", "envDefault", "envSeparator"
 // How to create a custom tag: https://github.com/caarlos0/env#changing-default-tag-name
 type NoSupportedTagOptionError struct {
 	Tag string