feat(i18n): implement localization using gettext files

- Recipe to extract new translations from the Go code: `make i18n_extract`
- Embedded `MO` files
- Detect language from environment variables
- Some strings were pluralized

Author: Goutte

Makefile

@@ -21,7 +21,7 @@ lint:
 
 test: install_deps
 	$(info ******************** running tests ********************)
-	go test -v ./...
+	LANGUAGE="en" go test -v ./...
 
 richtest: install_deps
 	$(info ******************** running tests with kyoh86/richgo ********************)
@@ -33,3 +33,7 @@ install_deps:
 
 clean:
 	rm -rf $(BIN)
+
+i18n_extract:
+	$(info ******************** extracting translation files ********************)
+	xgotext -v -in . -out locales

args.go

@@ -16,6 +16,7 @@ package cobra
 
 import (
 	"fmt"
+	"github.com/leonelquinteros/gotext"
 	"strings"
 )
 
@@ -33,15 +34,15 @@ func legacyArgs(cmd *Command, args []string) error {
 
 	// root command with subcommands, do subcommand checking.
 	if !cmd.HasParent() && len(args) > 0 {
-		return fmt.Errorf("unknown command %q for %q%s", args[0], cmd.CommandPath(), cmd.findSuggestions(args[0]))
+		return fmt.Errorf(gotext.Get("LegacyArgsValidationError"), args[0], cmd.CommandPath(), cmd.findSuggestions(args[0]))
 	}
 	return nil
 }
 
 // NoArgs returns an error if any args are included.
 func NoArgs(cmd *Command, args []string) error {
 	if len(args) > 0 {
-		return fmt.Errorf("unknown command %q for %q", args[0], cmd.CommandPath())
+		return fmt.Errorf(gotext.Get("NoArgsValidationError"), args[0], cmd.CommandPath())
 	}
 	return nil
 }
@@ -58,7 +59,7 @@ func OnlyValidArgs(cmd *Command, args []string) error {
 		}
 		for _, v := range args {
 			if !stringInSlice(v, validArgs) {
-				return fmt.Errorf("invalid argument %q for %q%s", v, cmd.CommandPath(), cmd.findSuggestions(args[0]))
+				return fmt.Errorf(gotext.Get("OnlyValidArgsValidationError"), v, cmd.CommandPath(), cmd.findSuggestions(args[0]))
 			}
 		}
 	}
@@ -74,7 +75,7 @@ func ArbitraryArgs(cmd *Command, args []string) error {
 func MinimumNArgs(n int) PositionalArgs {
 	return func(cmd *Command, args []string) error {
 		if len(args) < n {
-			return fmt.Errorf("requires at least %d arg(s), only received %d", n, len(args))
+			return fmt.Errorf(gotext.GetN("MinimumNArgsValidationError", "MinimumNArgsValidationErrorPlural", n), n, len(args))
 		}
 		return nil
 	}
@@ -84,7 +85,7 @@ func MinimumNArgs(n int) PositionalArgs {
 func MaximumNArgs(n int) PositionalArgs {
 	return func(cmd *Command, args []string) error {
 		if len(args) > n {
-			return fmt.Errorf("accepts at most %d arg(s), received %d", n, len(args))
+			return fmt.Errorf(gotext.GetN("MaximumNArgsValidationError", "MaximumNArgsValidationErrorPlural", n), n, len(args))
 		}
 		return nil
 	}
@@ -94,7 +95,7 @@ func MaximumNArgs(n int) PositionalArgs {
 func ExactArgs(n int) PositionalArgs {
 	return func(cmd *Command, args []string) error {
 		if len(args) != n {
-			return fmt.Errorf("accepts %d arg(s), received %d", n, len(args))
+			return fmt.Errorf(gotext.GetN("ExactArgsValidationError", "ExactArgsValidationErrorPlural", n), n, len(args))
 		}
 		return nil
 	}
@@ -104,7 +105,7 @@ func ExactArgs(n int) PositionalArgs {
 func RangeArgs(min int, max int) PositionalArgs {
 	return func(cmd *Command, args []string) error {
 		if len(args) < min || len(args) > max {
-			return fmt.Errorf("accepts between %d and %d arg(s), received %d", min, max, len(args))
+			return fmt.Errorf(gotext.GetN("RangeArgsValidationError", "RangeArgsValidationErrorPlural", max), min, max, len(args))
 		}
 		return nil
 	}

args_test.go

@@ -68,7 +68,7 @@ func minimumNArgsWithLessArgs(err error, t *testing.T) {
 		t.Fatal("Expected an error")
 	}
 	got := err.Error()
-	expected := "requires at least 2 arg(s), only received 1"
+	expected := "requires at least 2 args, only received 1"
 	if got != expected {
 		t.Fatalf("Expected %q, got %q", expected, got)
 	}
@@ -79,7 +79,7 @@ func maximumNArgsWithMoreArgs(err error, t *testing.T) {
 		t.Fatal("Expected an error")
 	}
 	got := err.Error()
-	expected := "accepts at most 2 arg(s), received 3"
+	expected := "accepts at most 2 args, received 3"
 	if got != expected {
 		t.Fatalf("Expected %q, got %q", expected, got)
 	}
@@ -90,7 +90,7 @@ func exactArgsWithInvalidCount(err error, t *testing.T) {
 		t.Fatal("Expected an error")
 	}
 	got := err.Error()
-	expected := "accepts 2 arg(s), received 3"
+	expected := "accepts 2 args, received 3"
 	if got != expected {
 		t.Fatalf("Expected %q, got %q", expected, got)
 	}
@@ -101,7 +101,7 @@ func rangeArgsWithInvalidCount(err error, t *testing.T) {
 		t.Fatal("Expected an error")
 	}
 	got := err.Error()
-	expected := "accepts between 2 and 4 arg(s), received 1"
+	expected := "accepts between 2 and 4 args, received 1"
 	if got != expected {
 		t.Fatalf("Expected %q, got %q", expected, got)
 	}

cobra.go

@@ -19,6 +19,7 @@ package cobra
 
 import (
 	"fmt"
+	"github.com/leonelquinteros/gotext"
 	"io"
 	"os"
 	"reflect"
@@ -230,7 +231,7 @@ func stringInSlice(a string, list []string) bool {
 // CheckErr prints the msg with the prefix 'Error:' and exits with error code 1. If the msg is nil, it does nothing.
 func CheckErr(msg interface{}) {
 	if msg != nil {
-		fmt.Fprintln(os.Stderr, "Error:", msg)
+		fmt.Fprintln(os.Stderr, gotext.Get("Error")+":", msg)
 		os.Exit(1)
 	}
 }

command.go

@@ -21,6 +21,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"github.com/leonelquinteros/gotext"
 	"io"
 	"os"
 	"path/filepath"
@@ -44,6 +45,12 @@ type Group struct {
 	Title string
 }
 
+// CommandUsageTemplateData is the data passed to the template of command usage
+type CommandUsageTemplateData struct {
+	*Command
+	I18n *i18nCommandGlossary
+}
+
 // Command is just that, a command for your application.
 // E.g.  'go run ...' - 'run' is the command. Cobra requires
 // you to define the usage and description as part of your command
@@ -432,7 +439,11 @@ func (c *Command) UsageFunc() (f func(*Command) error) {
 	}
 	return func(c *Command) error {
 		c.mergePersistentFlags()
-		err := tmpl(c.OutOrStderr(), c.UsageTemplate(), c)
+		data := CommandUsageTemplateData{
+			Command: c,
+			I18n:    getCommandGlossary(),
+		}
+		err := tmpl(c.OutOrStderr(), c.UsageTemplate(), data)
 		if err != nil {
 			c.PrintErrln(err)
 		}
@@ -549,35 +560,35 @@ func (c *Command) UsageTemplate() string {
 	if c.HasParent() {
 		return c.parent.UsageTemplate()
 	}
-	return `Usage:{{if .Runnable}}
+	return `{{.I18n.SectionUsage}}:{{if .Runnable}}
   {{.UseLine}}{{end}}{{if .HasAvailableSubCommands}}
   {{.CommandPath}} [command]{{end}}{{if gt (len .Aliases) 0}}
 
-Aliases:
+{{.I18n.SectionAliases}}:
   {{.NameAndAliases}}{{end}}{{if .HasExample}}
 
-Examples:
+{{.I18n.SectionExamples}}:
 {{.Example}}{{end}}{{if .HasAvailableSubCommands}}{{$cmds := .Commands}}{{if eq (len .Groups) 0}}
 
-Available Commands:{{range $cmds}}{{if (or .IsAvailableCommand (eq .Name "help"))}}
+{{.I18n.SectionAvailableCommands}}:{{range $cmds}}{{if (or .IsAvailableCommand (eq .Name "help"))}}
   {{rpad .Name .NamePadding }} {{.Short}}{{end}}{{end}}{{else}}{{range $group := .Groups}}
 
 {{.Title}}{{range $cmds}}{{if (and (eq .GroupID $group.ID) (or .IsAvailableCommand (eq .Name "help")))}}
   {{rpad .Name .NamePadding }} {{.Short}}{{end}}{{end}}{{end}}{{if not .AllChildCommandsHaveGroup}}
 
-Additional Commands:{{range $cmds}}{{if (and (eq .GroupID "") (or .IsAvailableCommand (eq .Name "help")))}}
+{{.I18n.SectionAdditionalCommands}}:{{range $cmds}}{{if (and (eq .GroupID "") (or .IsAvailableCommand (eq .Name "help")))}}
   {{rpad .Name .NamePadding }} {{.Short}}{{end}}{{end}}{{end}}{{end}}{{end}}{{if .HasAvailableLocalFlags}}
 
-Flags:
+{{.I18n.SectionFlags}}:
 {{.LocalFlags.FlagUsages | trimTrailingWhitespaces}}{{end}}{{if .HasAvailableInheritedFlags}}
 
-Global Flags:
+{{.I18n.SectionGlobalFlags}}:
 {{.InheritedFlags.FlagUsages | trimTrailingWhitespaces}}{{end}}{{if .HasHelpSubCommands}}
 
-Additional help topics:{{range .Commands}}{{if .IsAdditionalHelpTopicCommand}}
+{{.I18n.SectionAdditionalHelpTopics}}:{{range .Commands}}{{if .IsAdditionalHelpTopicCommand}}
   {{rpad .CommandPath .CommandPathPadding}} {{.Short}}{{end}}{{end}}{{end}}{{if .HasAvailableSubCommands}}
 
-Use "{{.CommandPath}} [command] --help" for more information about a command.{{end}}
+{{.I18n.Use}} "{{.CommandPath}} [command] --help" {{.I18n.ForInfoAboutCommand}}.{{end}}
 `
 }
 
@@ -756,7 +767,7 @@ func (c *Command) findSuggestions(arg string) string {
 	}
 	var sb strings.Builder
 	if suggestions := c.SuggestionsFor(arg); len(suggestions) > 0 {
-		sb.WriteString("\n\nDid you mean this?\n")
+		sb.WriteString("\n\n" + gotext.Get("DidYouMeanThis") + "\n")
 		for _, s := range suggestions {
 			_, _ = fmt.Fprintf(&sb, "\t%v\n", s)
 		}
@@ -877,7 +888,7 @@ func (c *Command) execute(a []string) (err error) {
 	}
 
 	if len(c.Deprecated) > 0 {
-		c.Printf("Command %q is deprecated, %s\n", c.Name(), c.Deprecated)
+		c.Printf(gotext.Get("CommandDeprecatedWarning")+"\n", c.Name(), c.Deprecated)
 	}
 
 	// initialize help and version flag at the last point possible to allow for user
@@ -1096,7 +1107,7 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 		}
 		if !c.SilenceErrors {
 			c.PrintErrln(c.ErrPrefix(), err.Error())
-			c.PrintErrf("Run '%v --help' for usage.\n", c.CommandPath())
+			c.PrintErrf(gotext.Get("RunHelpTip")+"\n", c.CommandPath())
 		}
 		return c, err
 	}
@@ -1162,7 +1173,7 @@ func (c *Command) ValidateRequiredFlags() error {
 	})
 
 	if len(missingFlagNames) > 0 {
-		return fmt.Errorf(`required flag(s) "%s" not set`, strings.Join(missingFlagNames, `", "`))
+		return fmt.Errorf(gotext.GetN("FlagNotSetError", "FlagNotSetErrorPlural", len(missingFlagNames)), strings.Join(missingFlagNames, `", "`))
 	}
 	return nil
 }
@@ -1186,9 +1197,9 @@ func (c *Command) checkCommandGroups() {
 func (c *Command) InitDefaultHelpFlag() {
 	c.mergePersistentFlags()
 	if c.Flags().Lookup("help") == nil {
-		usage := "help for "
+		usage := gotext.Get("HelpFor") + " "
 		if c.Name() == "" {
-			usage += "this command"
+			usage += gotext.Get("ThisCommand")
 		} else {
 			usage += c.Name()
 		}
@@ -1208,9 +1219,9 @@ func (c *Command) InitDefaultVersionFlag() {
 
 	c.mergePersistentFlags()
 	if c.Flags().Lookup("version") == nil {
-		usage := "version for "
+		usage := gotext.Get("VersionFor") + " "
 		if c.Name() == "" {
-			usage += "this command"
+			usage += gotext.Get("ThisCommand")
 		} else {
 			usage += c.Name()
 		}
@@ -1233,10 +1244,9 @@ func (c *Command) InitDefaultHelpCmd() {
 
 	if c.helpCommand == nil {
 		c.helpCommand = &Command{
-			Use:   "help [command]",
-			Short: "Help about any command",
-			Long: `Help provides help for any command in the application.
-Simply type ` + c.Name() + ` help [path to command] for full details.`,
+			Use:   fmt.Sprintf("help [%s]", gotext.Get("command")),
+			Short: gotext.Get("CommandHelpShort"),
+			Long:  fmt.Sprintf(gotext.Get("CommandHelpLong"), c.Name()+fmt.Sprintf(" help [%s]", gotext.Get("command"))),
 			ValidArgsFunction: func(c *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
 				var completions []string
 				cmd, _, e := c.Root().Find(args)
@@ -1259,7 +1269,7 @@ Simply type ` + c.Name() + ` help [path to command] for full details.`,
 			Run: func(c *Command, args []string) {
 				cmd, _, e := c.Root().Find(args)
 				if cmd == nil || e != nil {
-					c.Printf("Unknown help topic %#q\n", args)
+					c.Printf(gotext.Get("CommandHelpUnknownTopicError")+"\n", args)
 					CheckErr(c.Root().Usage())
 				} else {
 					cmd.InitDefaultHelpFlag()    // make possible 'help' flag to be shown

command_test.go

@@ -815,6 +815,21 @@ func TestPersistentFlagsOnChild(t *testing.T) {
 	}
 }
 
+func TestRequiredFlag(t *testing.T) {
+	c := &Command{Use: "c", Run: emptyRun}
+	c.Flags().String("foo1", "", "")
+	assertNoErr(t, c.MarkFlagRequired("foo1"))
+
+	expected := fmt.Sprintf("required flag %q is not set", "foo1")
+
+	_, err := executeCommand(c)
+	got := err.Error()
+
+	if got != expected {
+		t.Errorf("Expected error: %q, got: %q", expected, got)
+	}
+}
+
 func TestRequiredFlags(t *testing.T) {
 	c := &Command{Use: "c", Run: emptyRun}
 	c.Flags().String("foo1", "", "")
@@ -823,7 +838,7 @@ func TestRequiredFlags(t *testing.T) {
 	assertNoErr(t, c.MarkFlagRequired("foo2"))
 	c.Flags().String("bar", "", "")
 
-	expected := fmt.Sprintf("required flag(s) %q, %q not set", "foo1", "foo2")
+	expected := fmt.Sprintf("required flags %q, %q are not set", "foo1", "foo2")
 
 	_, err := executeCommand(c)
 	got := err.Error()
@@ -850,7 +865,7 @@ func TestPersistentRequiredFlags(t *testing.T) {
 
 	parent.AddCommand(child)
 
-	expected := fmt.Sprintf("required flag(s) %q, %q, %q, %q not set", "bar1", "bar2", "foo1", "foo2")
+	expected := fmt.Sprintf("required flags %q, %q, %q, %q are not set", "bar1", "bar2", "foo1", "foo2")
 
 	_, err := executeCommand(parent, "child")
 	if err.Error() != expected {