feat(pack): add support for scaffolding new extensions

internal/commands/commands.go

@@ -25,6 +25,7 @@ type PackClient interface {
 	NewBuildpack(context.Context, client.NewBuildpackOptions) error
 	PackageBuildpack(ctx context.Context, opts client.PackageBuildpackOptions) error
 	PackageExtension(ctx context.Context, opts client.PackageBuildpackOptions) error
+	NewExtension(ctx context.Context, options client.NewExtensionOptions) error
 	Build(context.Context, client.BuildOptions) error
 	RegisterBuildpack(context.Context, client.RegisterBuildpackOptions) error
 	YankBuildpack(client.YankBuildpackOptions) error

internal/commands/extension.go

@@ -19,7 +19,7 @@ func NewExtensionCommand(logger logging.Logger, cfg config.Config, client PackCl
 	// client and packageConfigReader to be passed later on
 	cmd.AddCommand(ExtensionPackage(logger, cfg, client, packageConfigReader))
 	// client to be passed later on
-	cmd.AddCommand(ExtensionNew(logger))
+	cmd.AddCommand(ExtensionNew(logger, client))
 	cmd.AddCommand(ExtensionPull(logger, cfg, client))
 	cmd.AddCommand(ExtensionRegister(logger, cfg, client))
 	cmd.AddCommand(ExtensionYank(logger, cfg, client))

internal/commands/extension_new.go

@@ -1,8 +1,17 @@
 package commands
 
 import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
 	"github.com/spf13/cobra"
 
+	"github.com/buildpacks/pack/internal/style"
+	"github.com/buildpacks/pack/pkg/client"
+	"github.com/buildpacks/pack/pkg/dist"
 	"github.com/buildpacks/pack/pkg/logging"
 )
 
@@ -15,21 +24,66 @@ type ExtensionNewFlags struct {
 }
 
 // extensioncreator type to be added here and argument also to be added in the function
+type ExtensionCreator interface {
+	NewExtension(ctx context.Context, options client.NewExtensionOptions) error
+}
 
 // ExtensionNew generates the scaffolding of an extension
-func ExtensionNew(logger logging.Logger) *cobra.Command {
+func ExtensionNew(logger logging.Logger, creator ExtensionCreator) *cobra.Command {
+	var flags ExtensionNewFlags
 	cmd := &cobra.Command{
 		Use:     "new <id>",
 		Short:   "Creates basic scaffolding of an extension",
 		Args:    cobra.MatchAll(cobra.ExactArgs(1), cobra.OnlyValidArgs),
 		Example: "pack extension new <example-extension>",
 		RunE: logError(logger, func(cmd *cobra.Command, args []string) error {
-			// logic will go here
+			id := args[0]
+			idParts := strings.Split(id, "/")
+			dirName := idParts[len(idParts)-1]
+
+			var path string
+			if len(flags.Path) == 0 {
+				cwd, err := os.Getwd()
+				if err != nil {
+					return err
+				}
+				path = filepath.Join(cwd, dirName)
+			} else {
+				path = flags.Path
+			}
+
+			_, err := os.Stat(path)
+			if !os.IsNotExist(err) {
+				return fmt.Errorf("directory %s exists", style.Symbol(path))
+			}
+
+			var stacks []dist.Stack
+			for _, s := range flags.Stacks {
+				stacks = append(stacks, dist.Stack{
+					ID:     s,
+					Mixins: []string{},
+				})
+			}
+
+			if err := creator.NewExtension(cmd.Context(), client.NewExtensionOptions{
+				API:     flags.API,
+				ID:      id,
+				Path:    path,
+				Stacks:  stacks,
+				Version: flags.Version,
+			}); err != nil {
+				return err
+			}
+
+			logger.Infof("Successfully created %s", style.Symbol(id))
 			return nil
 		}),
 	}
-
-	// flags will go here
+	cmd.Flags().StringVarP(&flags.API, "api", "a", "0.8", "Extension API compatibility of the generated buildpack")
+	cmd.Flags().StringVarP(&flags.Path, "path", "p", "", "Path to generate the extension")
+	cmd.Flags().StringVarP(&flags.Version, "version", "V", "1.0.0", "Version of the generated extension")
+	cmd.Flags().StringSliceVarP(&flags.Stacks, "stacks", "s", nil, "Stack(s) this buildpack will be compatible with"+stringSliceHelp("stack"))
+	cmd.Flags().MarkDeprecated("stacks", "prefer `--targets` instead: https://github.com/buildpacks/rfcs/blob/main/text/0096-remove-stacks-mixins.md")
 
 	AddHelpFlag(cmd, "new")
 	return cmd

pkg/client/new_extension.go

@@ -0,0 +1,91 @@
+package client
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+
+	"github.com/BurntSushi/toml"
+
+	"github.com/buildpacks/lifecycle/api"
+
+	"github.com/buildpacks/pack/internal/style"
+	"github.com/buildpacks/pack/pkg/dist"
+)
+
+type NewExtensionOptions struct {
+	// api compat version of the output extension artifact.
+	API string
+
+	// The base directory to generate assets
+	Path string
+
+	// The ID of the output extension artifact.
+	ID string
+
+	// version of the output extension artifact.
+	Version string
+
+	// Deprecated: The stacks this extension will work with
+	Stacks []dist.Stack
+}
+
+func (c *Client) NewExtension(ctx context.Context, opts NewExtensionOptions) error {
+	err := createExtensionTOML(opts.Path, opts.ID, opts.Version, opts.API, c)
+	if err != nil {
+		return err
+	}
+	return createBashExtension(opts.Path, c)
+}
+
+func createBashExtension(path string, c *Client) error {
+	if err := createBinScript(path, "build", bashBinBuild, c); err != nil {
+		return err
+	}
+
+	if err := createBinScript(path, "detect", bashBinDetect, c); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func createExtensionTOML(path, id, version, apiStr string, c *Client) error {
+	api, err := api.NewVersion(apiStr)
+	if err != nil {
+		return err
+	}
+
+	extensionTOML := dist.ExtensionDescriptor{
+		WithAPI: api,
+		WithInfo: dist.ModuleInfo{
+			ID:      id,
+			Version: version,
+		},
+	}
+
+	// The following line's comment is for gosec, it will ignore rule 301 in this case
+	// G301: Expect directory permissions to be 0750 or less
+	/* #nosec G301 */
+	if err := os.MkdirAll(path, 0755); err != nil {
+		return err
+	}
+
+	extensionTOMLPath := filepath.Join(path, "extension.toml")
+	_, err = os.Stat(extensionTOMLPath)
+	if os.IsNotExist(err) {
+		f, err := os.Create(extensionTOMLPath)
+		if err != nil {
+			return err
+		}
+		if err := toml.NewEncoder(f).Encode(extensionTOML); err != nil {
+			return err
+		}
+		defer f.Close()
+		if c != nil {
+			c.logger.Infof("    %s  extension.toml", style.Symbol("create"))
+		}
+	}
+
+	return nil
+}