generate: allow passing - for stdout output

Since generating completions to stdout for multiple shells does not make
sense, enforce `-` is supplied only once.

changelog/unreleased/issue-2511

@@ -0,0 +1,6 @@
+Enhancement: Allow generating shell completions to stdout
+
+Restic `generate` now supports passing `-` passed as file name to `--[shell]-completion` option.
+
+https://github.com/restic/restic/issues/2511
+https://github.com/restic/restic/pull/5053

cmd/restic/cmd_generate.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"io"
+	"os"
 	"time"
 
 	"github.com/restic/restic/internal/errors"
@@ -41,10 +43,10 @@ func init() {
 	cmdRoot.AddCommand(cmdGenerate)
 	fs := cmdGenerate.Flags()
 	fs.StringVar(&genOpts.ManDir, "man", "", "write man pages to `directory`")
-	fs.StringVar(&genOpts.BashCompletionFile, "bash-completion", "", "write bash completion `file`")
-	fs.StringVar(&genOpts.FishCompletionFile, "fish-completion", "", "write fish completion `file`")
-	fs.StringVar(&genOpts.ZSHCompletionFile, "zsh-completion", "", "write zsh completion `file`")
-	fs.StringVar(&genOpts.PowerShellCompletionFile, "powershell-completion", "", "write powershell completion `file`")
+	fs.StringVar(&genOpts.BashCompletionFile, "bash-completion", "", "write bash completion `file` (`-` for stdout)")
+	fs.StringVar(&genOpts.FishCompletionFile, "fish-completion", "", "write fish completion `file` (`-` for stdout)")
+	fs.StringVar(&genOpts.ZSHCompletionFile, "zsh-completion", "", "write zsh completion `file` (`-` for stdout)")
+	fs.StringVar(&genOpts.PowerShellCompletionFile, "powershell-completion", "", "write powershell completion `file` (`-` for stdout)")
 }
 
 func writeManpages(dir string) error {
@@ -65,32 +67,44 @@ func writeManpages(dir string) error {
 	return doc.GenManTree(cmdRoot, header, dir)
 }
 
-func writeBashCompletion(file string) error {
+func writeCompletion(filename string, shell string, generate func(w io.Writer) error) (err error) {
 	if stdoutIsTerminal() {
-		Verbosef("writing bash completion file to %v\n", file)
+		Verbosef("writing %s completion file to %v\n", shell, filename)
 	}
-	return cmdRoot.GenBashCompletionFile(file)
+	var outWriter io.Writer
+	if filename != "-" {
+		var outFile *os.File
+		outFile, err = os.Create(filename)
+		if err != nil {
+			return
+		}
+		defer func() { err = outFile.Close() }()
+		outWriter = outFile
+	} else {
+		outWriter = globalOptions.stdout
+	}
+
+	err = generate(outWriter)
+	return
 }
 
-func writeFishCompletion(file string) error {
-	if stdoutIsTerminal() {
-		Verbosef("writing fish completion file to %v\n", file)
+func checkStdoutForSingleShell(opts generateOptions) error {
+	completionFileOpts := []string{
+		opts.BashCompletionFile,
+		opts.FishCompletionFile,
+		opts.ZSHCompletionFile,
+		opts.PowerShellCompletionFile,
 	}
-	return cmdRoot.GenFishCompletionFile(file, true)
-}
-
-func writeZSHCompletion(file string) error {
-	if stdoutIsTerminal() {
-		Verbosef("writing zsh completion file to %v\n", file)
+	seenIsStdout := false
+	for _, completionFileOpt := range completionFileOpts {
+		if completionFileOpt == "-" {
+			if seenIsStdout {
+				return errors.Fatal("the generate command can generate shell completions to stdout for single shell only")
+			}
+			seenIsStdout = true
+		}
 	}
-	return cmdRoot.GenZshCompletionFile(file)
-}
-
-func writePowerShellCompletion(file string) error {
-	if stdoutIsTerminal() {
-		Verbosef("writing powershell completion file to %v\n", file)
-	}
-	return cmdRoot.GenPowerShellCompletionFile(file)
+	return nil
 }
 
 func runGenerate(opts generateOptions, args []string) error {
@@ -105,29 +119,34 @@ func runGenerate(opts generateOptions, args []string) error {
 		}
 	}
 
+	err := checkStdoutForSingleShell(opts)
+	if err != nil {
+		return err
+	}
+
 	if opts.BashCompletionFile != "" {
-		err := writeBashCompletion(opts.BashCompletionFile)
+		err := writeCompletion(opts.BashCompletionFile, "bash", cmdRoot.GenBashCompletion)
 		if err != nil {
 			return err
 		}
 	}
 
 	if opts.FishCompletionFile != "" {
-		err := writeFishCompletion(opts.FishCompletionFile)
+		err := writeCompletion(opts.FishCompletionFile, "fish", func(w io.Writer) error { return cmdRoot.GenFishCompletion(w, true) })
 		if err != nil {
 			return err
 		}
 	}
 
 	if opts.ZSHCompletionFile != "" {
-		err := writeZSHCompletion(opts.ZSHCompletionFile)
+		err := writeCompletion(opts.ZSHCompletionFile, "zsh", cmdRoot.GenZshCompletion)
 		if err != nil {
 			return err
 		}
 	}
 
 	if opts.PowerShellCompletionFile != "" {
-		err := writePowerShellCompletion(opts.PowerShellCompletionFile)
+		err := writeCompletion(opts.PowerShellCompletionFile, "powershell", cmdRoot.GenPowerShellCompletion)
 		if err != nil {
 			return err
 		}

cmd/restic/cmd_generate_integration_test.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	rtest "github.com/restic/restic/internal/test"
+)
+
+func TestGenerateStdout(t *testing.T) {
+	testCases := []struct {
+		name string
+		opts generateOptions
+	}{
+		{"bash", generateOptions{BashCompletionFile: "-"}},
+		{"fish", generateOptions{FishCompletionFile: "-"}},
+		{"zsh", generateOptions{ZSHCompletionFile: "-"}},
+		{"powershell", generateOptions{PowerShellCompletionFile: "-"}},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			buf := bytes.NewBuffer(nil)
+			globalOptions.stdout = buf
+			err := runGenerate(tc.opts, []string{})
+			rtest.OK(t, err)
+			completionString := buf.String()
+			rtest.Assert(t, strings.Contains(completionString, "# "+tc.name+" completion for restic"), "has no expected completion header")
+		})
+	}
+
+	t.Run("Generate shell completions to stdout for two shells", func(t *testing.T) {
+		buf := bytes.NewBuffer(nil)
+		globalOptions.stdout = buf
+		opts := generateOptions{BashCompletionFile: "-", FishCompletionFile: "-"}
+		err := runGenerate(opts, []string{})
+		rtest.Assert(t, err != nil, "generate shell completions to stdout for two shells fails")
+	})
+}