feat: notEmpty tag (#174)

Signed-off-by: Carlos A Becker <caarlos0@gmail.com>

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://img.shields.io/github/workflow/status/caarlos0/env/build?style=for-the-badge)](https://github.com/caarlos0/env/actions?workflow=build)
 [![Coverage Status](https://img.shields.io/codecov/c/gh/caarlos0/env.svg?logo=codecov&style=for-the-badge)](https://codecov.io/gh/caarlos0/env)
-[![](http://img.shields.io/badge/godoc-reference-5272B4.svg?style=for-the-badge)](http://godoc.org/github.com/caarlos0/env/v6)
+[![](http://img.shields.io/badge/godoc-reference-5272B4.svg?style=for-the-badge)](https://pkg.go.dev/github.com/caarlos0/env/v6)
 
 Simple lib to parse envs to structs in Go.
 
@@ -17,11 +17,7 @@ import (
 	"fmt"
 	"time"
 
-	// if using go modules
 	"github.com/caarlos0/env/v6"
-
-	// if using dep/others
-	"github.com/caarlos0/env"
 )
 
 type config struct {
@@ -142,18 +138,25 @@ And then you can parse `Config` with `env.Parse`.
 
 ## Required fields
 
-The `env` tag option `required` (e.g., `env:"tagKey,required"`) can be added
-to ensure that some environment variable is set.  In the example above,
-an error is returned if the `config` struct is changed to:
+The `env` tag option `required` (e.g., `env:"tagKey,required"`) can be added to ensure that some environment variable is set.
+In the example above, an error is returned if the `config` struct is changed to:
+
+```go
+type config struct {
+	SecretKey string `env:"SECRET_KEY,required"`
+}
+```
+
+## Not Empty fields
 
+While `required` demands the environment variable to be check, it doesn't check its value.
+If you want to make sure the environment is set and not emtpy, you need to use the `notEmpty` tag option instead (`env:"SOME_ENV,notEmpty"`).
+
+Example:
 
 ```go
 type config struct {
-	Home         string   `env:"HOME"`
-	Port         int      `env:"PORT" envDefault:"3000"`
-	IsProduction bool     `env:"PRODUCTION"`
-	Hosts        []string `env:"HOSTS" envSeparator:":"`
-	SecretKey    string   `env:"SECRET_KEY,required"`
+	SecretKey string `env:"SECRET_KEY,notEmpty"`
 }
 ```
 
@@ -183,7 +186,7 @@ package main
 import (
 	"fmt"
 	"time"
-	"github.com/caarlos0/env"
+	"github.com/caarlos0/env/v6"
 )
 
 type config struct {
@@ -213,7 +216,6 @@ $ SECRET=/tmp/secret  \
 {Secret:qwerty Password:dvorak Certificate:coleman}
 ```
 
-
 ## Options
 
 ### Environment
@@ -231,7 +233,7 @@ import (
 	"fmt"
 	"log"
 
-	"github.com/caarlos0/env"
+	"github.com/caarlos0/env/v6"
 )
 
 type Config struct {
@@ -267,7 +269,7 @@ import (
 	"fmt"
 	"log"
 
-	"github.com/caarlos0/env"
+	"github.com/caarlos0/env/v6"
 )
 
 type Config struct {

env.go

@@ -219,6 +219,7 @@ func get(field reflect.StructField, opts []Options) (val string, err error) {
 	var exists bool
 	var loadFile bool
 	var unset bool
+	var notEmpty bool
 	expand := strings.EqualFold(field.Tag.Get("envExpand"), "true")
 
 	key, tags := parseKeyForOption(field.Tag.Get(getTagName(opts)))
@@ -233,6 +234,8 @@ func get(field reflect.StructField, opts []Options) (val string, err error) {
 			required = true
 		case "unset":
 			unset = true
+		case "notEmpty":
+			notEmpty = true
 		default:
 			return "", fmt.Errorf("env: tag option %q not supported", tag)
 		}
@@ -253,6 +256,10 @@ func get(field reflect.StructField, opts []Options) (val string, err error) {
 		return "", fmt.Errorf(`env: required environment variable %q is not set`, key)
 	}
 
+	if notEmpty && val == "" {
+		return "", fmt.Errorf("env: environment variable %q should not be empty", key)
+	}
+
 	if loadFile && val != "" {
 		filename := val
 		val, err = getFromFile(filename)

env_test.go

@@ -684,6 +684,44 @@ func TestErrorRequiredNotSet(t *testing.T) {
 	isErrorWithMessage(t, Parse(&config{}), `env: required environment variable "IS_REQUIRED" is not set`)
 }
 
+func TestNoErrorNotEmptySet(t *testing.T) {
+	is := is.New(t)
+	os.Setenv("IS_REQUIRED", "1")
+	defer os.Clearenv()
+	type config struct {
+		IsRequired string `env:"IS_REQUIRED,notEmpty"`
+	}
+	is.NoErr(Parse(&config{}))
+}
+
+func TestNoErrorRequiredAndNotEmptySet(t *testing.T) {
+	is := is.New(t)
+	os.Setenv("IS_REQUIRED", "1")
+	defer os.Clearenv()
+	type config struct {
+		IsRequired string `env:"IS_REQUIRED,required,notEmpty"`
+	}
+	is.NoErr(Parse(&config{}))
+}
+
+func TestErrorNotEmptySet(t *testing.T) {
+	os.Setenv("IS_REQUIRED", "")
+	defer os.Clearenv()
+	type config struct {
+		IsRequired string `env:"IS_REQUIRED,notEmpty"`
+	}
+	isErrorWithMessage(t, Parse(&config{}), `env: environment variable "IS_REQUIRED" should not be empty`)
+}
+
+func TestErrorRequiredAndNotEmptySet(t *testing.T) {
+	os.Setenv("IS_REQUIRED", "")
+	defer os.Clearenv()
+	type config struct {
+		IsRequired string `env:"IS_REQUIRED,notEmpty,required"`
+	}
+	isErrorWithMessage(t, Parse(&config{}), `env: environment variable "IS_REQUIRED" should not be empty`)
+}
+
 func TestErrorRequiredNotSetWithDefault(t *testing.T) {
 	is := is.New(t)