Добавлены функции вывода в поток описания параметров.

.golangci.yaml

@@ -184,6 +184,29 @@ linters-settings:
       - name: unexported-return
         disabled: true
 
+  varnamelen:
+    # The longest distance, in source lines, that is being considered a "small scope".
+    # Variables used in at most this many lines will be ignored.
+    # Default: 5
+    max-distance: 6
+    # The minimum length of a variable's name that is considered "long".
+    # Variable names that are at least this long will be ignored.
+    # Default: 3
+    min-name-length: 2
+    # Ignore "ok" variables that hold the bool return value of a type assertion.
+    # Default: false
+    ignore-type-assert-ok: true
+    # Ignore "ok" variables that hold the bool return value of a map index.
+    # Default: false
+    ignore-map-index-ok: true
+    # Ignore "ok" variables that hold the bool return value of a channel receive.
+    # Default: false
+    ignore-chan-recv-ok: true
+    # Optional list of variable names that should be ignored completely.
+    # Default: []
+    ignore-names:
+      - err
+
 # output configuration options
 output:
   # The formats used to render issues.

cli.go

@@ -18,6 +18,7 @@ package config
 import (
 	"flag"
 	"fmt"
+	"io"
 	"reflect"
 	"strconv"
 	"unsafe"
@@ -313,3 +314,15 @@ func (c *Command) Parse(args []string) error {
 
 	return nil
 }
+
+// PrintUsage prints command description
+func (c *Command) PrintUsage(w io.Writer) error {
+	if _, err := w.Write([]byte(c.Usage + "\n")); err != nil {
+		return fmt.Errorf("write usage: %w", err)
+	}
+
+	c.FlagSet.SetOutput(w)
+	c.FlagSet.Usage()
+
+	return nil
+}

cli_test.go

@@ -17,6 +17,7 @@ package config
 
 import (
 	"flag"
+	"os"
 	"strconv"
 	"testing"
 
@@ -29,9 +30,7 @@ func TestServiceCommand(t *testing.T) {
 	serviceConfig := test.ServiceConfig{}
 	cmd := NewCLI("Service")
 	err := cmd.Init(&serviceConfig)
-	if err != nil {
+	assert.NoError(err, "init service command")
-		t.Errorf("Can't init service command. %s", err.Error())
-	}
 
 	// assert service cmd
 	assert.NotNil(cmd.FlagSet)
@@ -62,6 +61,15 @@ func TestServiceCommand(t *testing.T) {
 	assert.NotNil(cmd.FlagSet.Lookup("log-level"))
 }
 
+func TestPrintUsage(t *testing.T) {
+	assert := assert.New(t)
+	serviceConfig := test.ServiceConfig{}
+	cmd := NewCLI("Service")
+	err := cmd.Init(&serviceConfig)
+	assert.NoError(err, "init service command")
+	assert.NoError(cmd.PrintUsage(os.Stdout))
+}
+
 func TestLoginSubCommand(t *testing.T) {
 	assert := assert.New(t)
 	serviceConfig := test.ServiceConfig{Login: &test.LoginConfig{}}
@@ -256,5 +264,3 @@ func TestCommandWithSlices(t *testing.T) {
 	assert.Equal(200, conf.Values[1])
 	assert.Equal(300, conf.Values[2])
 }
-
-func TestUsage(t *testing.T) {}

env.go

@@ -16,21 +16,60 @@
 package config
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"os"
 	"reflect"
+	"strings"
 )
 
+// ParseValueEnvFunc func to parse env value
+type ParseValueEnvFunc func(value reflect.Value, prefix string) error
+
 // Parse parses given structure interface, extracts environment definitions
 // from its tag and sets structure with defined environment variables
-func ParseEnv(i interface{}) error {
+func ParseEnv(out interface{}) error {
-	return ParseEnvWith(i, "")
+	return ParseEnvWith(out, "", parseValueEnv)
 }
 
 // UsageEnv prints usage description of config i to out
-func UsageEnv(out io.Writer, i interface{}) {
+func UsageEnv(out io.Writer, in interface{}) error {
-	// STub
+	if _, err := out.Write([]byte("Environment Usage:\n")); err != nil {
+		return fmt.Errorf("write usage: %w", err)
+	}
+
+	buf := bytes.NewBufferString("")
+
+	if err := ParseEnvWith(in, "", func(value reflect.Value, prefix string) error {
+		return usageValueEnv(buf, value, prefix)
+	}); err != nil {
+		return err
+	}
+
+	var tabPos int
+
+	for _, line := range strings.Split(strings.TrimRight(buf.String(), "\n"), "\n") {
+		if pos := strings.Index(line, "\t"); pos > tabPos {
+			tabPos = pos
+		}
+	}
+
+	const TabSize = 8
+
+	for _, line := range strings.Split(strings.TrimRight(buf.String(), "\n"), "\n") {
+		if pos := strings.Index(line, "\t"); pos >= 0 {
+			if count := tabPos/TabSize - pos/TabSize; count > 0 {
+				line = line[:pos] + strings.Repeat("\t", count) + line[pos:]
+			}
+		}
+
+		if _, err := out.Write([]byte(line + "\n")); err != nil {
+			return fmt.Errorf("write usage: %w", err)
+		}
+	}
+
+	return nil
 }
 
 // ParseWith parses with given structure interface and environment name prefix
@@ -47,8 +86,8 @@ func UsageEnv(out io.Writer, i interface{}) {
 //
 // The Server.DB.Host will be mapped to environment variable: DB_HOST which is
 // concatenated from DB tag in Server struct and Host tag in Database struct
-func ParseEnvWith(i interface{}, prefix string) error {
+func ParseEnvWith(out interface{}, prefix string, parser ParseValueEnvFunc) error {
-	ptrRef := reflect.ValueOf(i)
+	ptrRef := reflect.ValueOf(out)
 
 	if ptrRef.IsNil() || ptrRef.Kind() != reflect.Ptr {
 		return fmt.Errorf("%w: %s",
@@ -61,7 +100,44 @@ func ParseEnvWith(i interface{}, prefix string) error {
 			errExpectStructPointerInsteadOf, valueOfStruct.Kind().String())
 	}
 
-	return parseValueEnv(valueOfStruct, prefix)
+	return parser(valueOfStruct, prefix)
+}
+
+func usageValueEnv(out io.Writer, value reflect.Value, prefix string) error {
+	var err error
+
+	typeOfStruct := value.Type()
+
+	for i := 0; i < value.NumField() && err == nil; i++ {
+		valueOfField := value.Field(i)
+		kindOfField := valueOfField.Kind()
+		structOfField := typeOfStruct.Field(i)
+
+		// Recursively unmarshal if value is ptr type
+		if kindOfField == reflect.Ptr {
+			if !valueOfField.IsNil() && valueOfField.CanSet() {
+				err = ParseEnvWith(
+					valueOfField.Interface(),
+					prefix+structOfField.Tag.Get("env"),
+					func(value reflect.Value, prefix string) error {
+						return usageValueEnv(out, value, prefix)
+					},
+				)
+			} else {
+				continue
+			}
+		} else if kindOfField == reflect.Struct {
+			err = usageValueEnv(out, valueOfField, prefix+structOfField.Tag.Get("env"))
+		}
+
+		if err != nil {
+			return err
+		}
+
+		err = usageFieldValueEnv(out, structOfField, prefix)
+	}
+
+	return err
 }
 
 // parseValue parses a reflect.Value object
@@ -78,8 +154,11 @@ func parseValueEnv(value reflect.Value, prefix string) error {
 		// Recursively unmarshal if value is ptr type
 		if kindOfField == reflect.Ptr {
 			if !valueOfField.IsNil() && valueOfField.CanSet() {
-				err = ParseEnvWith(valueOfField.Interface(),
+				err = ParseEnvWith(
-					prefix+structOfField.Tag.Get("env"))
+					valueOfField.Interface(),
+					prefix+structOfField.Tag.Get("env"),
+					parseValueEnv,
+				)
 			} else {
 				continue
 			}
@@ -160,3 +239,23 @@ func setFieldValueEnv(value reflect.Value, field reflect.StructField, prefix str
 
 	return nil
 }
+
+func usageFieldValueEnv(out io.Writer, field reflect.StructField, prefix string) error {
+	envName := field.Tag.Get("env")
+	if envName == "" {
+		return nil
+	}
+
+	envName = prefix + envName
+	msg := "   " + envName + "\t" + field.Tag.Get("usage")
+
+	if def := field.Tag.Get("default"); def != "" {
+		msg += " (default: " + def + ")"
+	}
+
+	if _, err := out.Write([]byte(msg + "\n")); err != nil {
+		return fmt.Errorf("write usage: %w", err)
+	}
+
+	return nil
+}

env_test.go

@@ -75,7 +75,7 @@ func TestLoginConfigEnvWithPrefix(t *testing.T) {
 	defer func() { _ = os.Unsetenv("DB_PASSWORD") }()
 
 	loginConfig := test.LoginConfig{}
-	assert.NoError(ParseEnvWith(&loginConfig, "DB_"))
+	assert.NoError(ParseEnvWith(&loginConfig, "DB_", parseValueEnv))
 	assert.Equal(LOGIN_USER, loginConfig.User)
 	assert.Equal(LOGIN_PASSWORD, loginConfig.Password)
 }
@@ -142,6 +142,11 @@ func TestServiceConfigEnv(t *testing.T) {
 	assert.Equal(DB_LOG_LEVEL, serviceConfig.DBConfig.Log.Level)
 }
 
+func TestEnvUsage(t *testing.T) {
+	conf := test.ServiceConfig{}
+	assert.NoError(t, UsageEnv(os.Stdout, &conf))
+}
+
 func TestServiceLoginConfigEnv(t *testing.T) {
 	var err error