Feature: Add required flag support

flag.go

@@ -11,4 +11,5 @@ type Flag struct {
 	DefValue   string // default value (as text); for usage message
 	Hidden     bool
 	Deprecated bool
+	Required   bool
 }

gen/gcli/gcli.go

@@ -15,12 +15,13 @@ func GenerateTo(src []*sflags.Flag, dst *[]cli.Flag) {
 			aliases = append(aliases, srcFlag.Short)
 		}
 		*dst = append(*dst, &cli.GenericFlag{
-			Name:    name,
-			EnvVars: []string{srcFlag.EnvName},
-			Aliases: aliases,
-			Hidden:  srcFlag.Hidden,
-			Usage:   srcFlag.Usage,
-			Value:   srcFlag.Value,
+			Name:     name,
+			EnvVars:  []string{srcFlag.EnvName},
+			Aliases:  aliases,
+			Hidden:   srcFlag.Hidden,
+			Usage:    srcFlag.Usage,
+			Value:    srcFlag.Value,
+			Required: srcFlag.Required,
 		})
 	}
 }

gen/gcli/gcli_test.go

@@ -3,6 +3,7 @@ package gcli
 import (
 	"errors"
 	"io"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -12,7 +13,7 @@ import (
 )
 
 type cfg1 struct {
-	StringValue1 string
+	StringValue1 string `flag:",required"`
 	StringValue2 string `flag:"string-value-two s"`
 
 	CounterValue1 sflags.Counter
@@ -68,18 +69,21 @@ func TestParse(t *testing.T) {
 				StringValue1: "string_value1_value",
 				StringValue2: "",
 			},
-			args: []string{},
+			args:    []string{},
+			expErr2: errors.New("required flag \"string-value1\" not set"),
 		},
 		{
 			name: "Test cfg1 short option",
 			cfg: &cfg1{
 				StringValue2: "string_value2_value",
 			},
 			expCfg: &cfg1{
+				StringValue1: "string_value1_value2",
 				StringValue2: "string_value2_value2",
 			},
 			args: []string{
 				"-s=string_value2_value2",
+				"--string-value1", "string_value1_value2",
 			},
 		},
 		{
@@ -142,7 +146,7 @@ func TestParse(t *testing.T) {
 			err = cliApp.Run(args)
 			if test.expErr2 != nil {
 				require.Error(t, err)
-				require.Equal(t, test.expErr2, err)
+				require.Equal(t, test.expErr2.Error(), strings.ToLower(err.Error()))
 			} else {
 				require.NoError(t, err)
 			}

gen/gcli/gcliv3.go

@@ -48,6 +48,7 @@ func GenerateToV3(src []*sflags.Flag, dst *[]cli.Flag) {
 			Value: &value{
 				v: srcFlag.Value,
 			},
+			Required: srcFlag.Required,
 		})
 	}
 }

gen/gcli/gcliv3_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"io"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -13,7 +14,7 @@ import (
 )
 
 type cfg2 struct {
-	StringValue1 string
+	StringValue1 string `flag:",required"`
 	StringValue2 string `flag:"string-value-two s"`
 
 	CounterValue1 sflags.Counter
@@ -69,18 +70,21 @@ func TestParseV3(t *testing.T) {
 				StringValue1: "string_value1_value",
 				StringValue2: "",
 			},
-			args: []string{},
+			args:    []string{},
+			expErr2: errors.New("required flag \"string-value1\" not set"),
 		},
 		{
 			name: "Test cfg2 short option",
 			cfg: &cfg2{
 				StringValue2: "string_value2_value",
 			},
 			expCfg: &cfg2{
+				StringValue1: "string_value1_value2",
 				StringValue2: "string_value2_value2",
 			},
 			args: []string{
 				"-s=string_value2_value2",
+				"--string-value1", "string_value1_value2",
 			},
 		},
 		{
@@ -143,7 +147,7 @@ func TestParseV3(t *testing.T) {
 			err = cmd.Run(context.Background(), args)
 			if test.expErr2 != nil {
 				require.Error(t, err)
-				require.Equal(t, test.expErr2, err)
+				require.Equal(t, test.expErr2.Error(), strings.ToLower(err.Error()))
 			} else {
 				require.NoError(t, err)
 			}

gen/gkingpin/gkingpin.go

@@ -23,6 +23,9 @@ func GenerateTo(src []*sflags.Flag, dst flagger) {
 		if srcFlag.Hidden {
 			flag.Hidden()
 		}
+		if srcFlag.Required {
+			flag.Required()
+		}
 		if srcFlag.Short != "" {
 			r, _ := utf8.DecodeRuneInString(srcFlag.Short)
 			if r != utf8.RuneError {

gen/gkingpin/gkingpin_test.go

@@ -11,7 +11,7 @@ import (
 )
 
 type cfg1 struct {
-	StringValue1 string
+	StringValue1 string `flag:",required"`
 	StringValue2 string `flag:"string-value-two s"`
 
 	CounterValue1 sflags.Counter
@@ -67,18 +67,21 @@ func TestParse(t *testing.T) {
 				StringValue1: "string_value1_value",
 				StringValue2: "",
 			},
-			args: []string{},
+			args:    []string{},
+			expErr2: errors.New("required flag(s) '--string-value1' not provided"),
 		},
 		{
 			name: "Test cfg1 short option",
 			cfg: &cfg1{
 				StringValue2: "string_value2_value",
 			},
 			expCfg: &cfg1{
+				StringValue1: "string_value1_value2",
 				StringValue2: "string_value2_value2",
 			},
 			args: []string{
 				"-s", "string_value2_value2",
+				"--string-value1", "string_value1_value2",
 			},
 		},
 		{

parser.go

@@ -114,7 +114,7 @@ func parseFlagTag(field reflect.StructField, opt opts) *Flag {
 		}
 		flag.Hidden = hasOption(flagTags[1:], "hidden")
 		flag.Deprecated = hasOption(flagTags[1:], "deprecated")
-
+		flag.Required = hasOption(flagTags[1:], "required")
 	}
 
 	if opt.prefix != "" && !ignoreFlagPrefix {

parser_test.go

@@ -27,6 +27,7 @@ func TestParseStruct(t *testing.T) {
 		Name4 *string
 		Name5 string `flag:"-"`
 		name6 string
+		Name7 int `flag:",required"`
 
 		Addr *net.TCPAddr
 
@@ -147,6 +148,13 @@ func TestParseStruct(t *testing.T) {
 					DefValue: "name_value4",
 					Value:    newStringValue(simpleCfg.Name4),
 				},
+				{
+					Name:     "name7",
+					EnvName:  "NAME7",
+					Required: true,
+					DefValue: "0",
+					Value:    newIntValue(&simpleCfg.Name7),
+				},
 				{
 					Name:     "addr",
 					EnvName:  "ADDR",
@@ -194,6 +202,13 @@ func TestParseStruct(t *testing.T) {
 					DefValue: "name_value4",
 					Value:    newStringValue(simpleCfg.Name4),
 				},
+				{
+					Name:     "name7",
+					EnvName:  "PP|NAME7",
+					Required: true,
+					DefValue: "0",
+					Value:    newIntValue(&simpleCfg.Name7),
+				},
 				{
 					Name:     "addr",
 					EnvName:  "PP|ADDR",