release/dist/cli: factor out the CLI boilerplace from cmd/dist

Signed-off-by: David Anderson <danderson@tailscale.com>

cmd/dist/dist.go

@@ -5,130 +5,21 @@ import (
 	"context"
 	"errors"
 	"flag"
-	"fmt"
 	"log"
 	"os"
-	"path/filepath"
-	"sort"
-	"strings"
-	"time"
 
-	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/release/dist"
+	"tailscale.com/release/dist/cli"
 	"tailscale.com/release/dist/unixpkgs"
 )
 
-func main() {
-	var targets []dist.Target
-	targets = append(targets, unixpkgs.Targets()...)
-	sort.Slice(targets, func(i, j int) bool {
-		return targets[i].String() < targets[j].String()
-	})
-
-	rootCmd := &ffcli.Command{
-		Name:       "dist",
-		ShortUsage: "dist [flags] <command> [command flags]",
-		ShortHelp:  "Build tailscale release packages for distribution",
-		LongHelp:   `For help on subcommands, add --help after: "dist list --help".`,
-		Subcommands: []*ffcli.Command{
-			{
-				Name: "list",
-				Exec: func(ctx context.Context, args []string) error {
-					return runList(ctx, args, targets)
-				},
-				ShortUsage: "dist list [target filters]",
-				ShortHelp:  "List all available release targets.",
-				LongHelp: strings.TrimSpace(`
-			If filters are provided, only targets matching at least one filter are listed.
-			Filters can use glob patterns (* and ?).
-			`),
-			},
-			{
-				Name: "build",
-				Exec: func(ctx context.Context, args []string) error {
-					return runBuild(ctx, args, targets)
-				},
-				ShortUsage: "dist build [target filters]",
-				ShortHelp:  "Build release files",
-				FlagSet: (func() *flag.FlagSet {
-					fs := flag.NewFlagSet("build", flag.ExitOnError)
-					fs.StringVar(&buildArgs.manifest, "manifest", "", "manifest file to write")
-					return fs
-				})(),
-				LongHelp: strings.TrimSpace(`
-			If filters are provided, only targets matching at least one filter are built.
-			Filters can use glob patterns (* and ?).
-			`),
-			},
-		},
-		Exec: func(context.Context, []string) error { return flag.ErrHelp },
-	}
-
-	if err := rootCmd.ParseAndRun(context.Background(), os.Args[1:]); err != nil && !errors.Is(err, flag.ErrHelp) {
-		log.Fatal(err)
-	}
-}
-
-func runList(ctx context.Context, filters []string, targets []dist.Target) error {
-	tgts, err := dist.FilterTargets(targets, filters)
-	if err != nil {
-		return err
-	}
-	for _, tgt := range tgts {
-		fmt.Println(tgt)
-	}
-	return nil
-}
-
-var buildArgs struct {
-	manifest string
+func getTargets() ([]dist.Target, error) {
+	return unixpkgs.Targets(), nil
 }
 
-func runBuild(ctx context.Context, filters []string, targets []dist.Target) error {
-	tgts, err := dist.FilterTargets(targets, filters)
-	if err != nil {
-		return err
-	}
-	if len(tgts) == 0 {
-		return errors.New("no targets matched (did you mean 'dist build all'?)")
-	}
-
-	st := time.Now()
-	wd, err := os.Getwd()
-	if err != nil {
-		return fmt.Errorf("getting working directory: %w", err)
-	}
-	b, err := dist.NewBuild(wd, filepath.Join(wd, "dist"))
-	if err != nil {
-		return fmt.Errorf("creating build context: %w", err)
-	}
-	defer b.Close()
-
-	out, err := b.Build(tgts)
-	if err != nil {
-		return fmt.Errorf("building targets: %w", err)
-	}
-
-	if buildArgs.manifest != "" {
-		// Make the built paths relative to the manifest file.
-		manifest, err := filepath.Abs(buildArgs.manifest)
-		if err != nil {
-			return fmt.Errorf("getting absolute path of manifest: %w", err)
-		}
-		fmt.Println(manifest)
-		fmt.Println(filepath.Join(b.Out, out[0]))
-		for i := range out {
-			rel, err := filepath.Rel(filepath.Dir(manifest), filepath.Join(b.Out, out[i]))
-			if err != nil {
-				return fmt.Errorf("making path relative: %w", err)
-			}
-			out[i] = rel
-		}
-		if err := os.WriteFile(manifest, []byte(strings.Join(out, "\n")), 0644); err != nil {
-			return fmt.Errorf("writing manifest: %w", err)
-		}
+func main() {
+	cmd := cli.CLI(getTargets)
+	if err := cmd.ParseAndRun(context.Background(), os.Args[1:]); err != nil && !errors.Is(err, flag.ErrHelp) {
+		log.Fatal(err)
 	}
-
-	fmt.Println("Done! Took", time.Since(st))
-	return nil
 }

release/dist/cli/cli.go

@@ -0,0 +1,134 @@
+// Package cli provides the skeleton of a CLI for building release packages.
+package cli
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/peterbourgon/ff/v3/ffcli"
+	"tailscale.com/release/dist"
+)
+
+// CLI returns a CLI root command to build release packages.
+//
+// getTargets is a function that gets run in the Exec function of commands that
+// need to know the target list. Its execution is deferred in this way to allow
+// customization of command FlagSets with flags that influence the target list.
+func CLI(getTargets func() ([]dist.Target, error)) *ffcli.Command {
+	return &ffcli.Command{
+		Name:       "dist",
+		ShortUsage: "dist [flags] <command> [command flags]",
+		ShortHelp:  "Build tailscale release packages for distribution",
+		LongHelp:   `For help on subcommands, add --help after: "dist list --help".`,
+		Subcommands: []*ffcli.Command{
+			{
+				Name: "list",
+				Exec: func(ctx context.Context, args []string) error {
+					targets, err := getTargets()
+					if err != nil {
+						return err
+					}
+					return runList(ctx, args, targets)
+				},
+				ShortUsage: "dist list [target filters]",
+				ShortHelp:  "List all available release targets.",
+				LongHelp: strings.TrimSpace(`
+			If filters are provided, only targets matching at least one filter are listed.
+			Filters can use glob patterns (* and ?).
+			`),
+			},
+			{
+				Name: "build",
+				Exec: func(ctx context.Context, args []string) error {
+					targets, err := getTargets()
+					if err != nil {
+						return err
+					}
+					return runBuild(ctx, args, targets)
+				},
+				ShortUsage: "dist build [target filters]",
+				ShortHelp:  "Build release files",
+				FlagSet: (func() *flag.FlagSet {
+					fs := flag.NewFlagSet("build", flag.ExitOnError)
+					fs.StringVar(&buildArgs.manifest, "manifest", "", "manifest file to write")
+					return fs
+				})(),
+				LongHelp: strings.TrimSpace(`
+			If filters are provided, only targets matching at least one filter are built.
+			Filters can use glob patterns (* and ?).
+			`),
+			},
+		},
+		Exec: func(context.Context, []string) error { return flag.ErrHelp },
+	}
+}
+
+func runList(ctx context.Context, filters []string, targets []dist.Target) error {
+	tgts, err := dist.FilterTargets(targets, filters)
+	if err != nil {
+		return err
+	}
+	for _, tgt := range tgts {
+		fmt.Println(tgt)
+	}
+	return nil
+}
+
+var buildArgs struct {
+	manifest string
+}
+
+func runBuild(ctx context.Context, filters []string, targets []dist.Target) error {
+	tgts, err := dist.FilterTargets(targets, filters)
+	if err != nil {
+		return err
+	}
+	if len(tgts) == 0 {
+		return errors.New("no targets matched (did you mean 'dist build all'?)")
+	}
+
+	st := time.Now()
+	wd, err := os.Getwd()
+	if err != nil {
+		return fmt.Errorf("getting working directory: %w", err)
+	}
+	b, err := dist.NewBuild(wd, filepath.Join(wd, "dist"))
+	if err != nil {
+		return fmt.Errorf("creating build context: %w", err)
+	}
+	defer b.Close()
+
+	out, err := b.Build(tgts)
+	if err != nil {
+		return fmt.Errorf("building targets: %w", err)
+	}
+
+	if buildArgs.manifest != "" {
+		// Make the built paths relative to the manifest file.
+		manifest, err := filepath.Abs(buildArgs.manifest)
+		if err != nil {
+			return fmt.Errorf("getting absolute path of manifest: %w", err)
+		}
+		fmt.Println(manifest)
+		fmt.Println(filepath.Join(b.Out, out[0]))
+		for i := range out {
+			rel, err := filepath.Rel(filepath.Dir(manifest), filepath.Join(b.Out, out[i]))
+			if err != nil {
+				return fmt.Errorf("making path relative: %w", err)
+			}
+			out[i] = rel
+		}
+		if err := os.WriteFile(manifest, []byte(strings.Join(out, "\n")), 0644); err != nil {
+			return fmt.Errorf("writing manifest: %w", err)
+		}
+	}
+
+	fmt.Println("Done! Took", time.Since(st))
+	return nil
+}