Add extension create command

pkg/cmd/extension/command.go

@@ -141,6 +141,39 @@ func NewCmdExtension(f *cmdutil.Factory) *cobra.Command {
 				return nil
 			},
 		},
+		&cobra.Command{
+			Use:   "create <name>",
+			Short: "Create a new extension",
+			Args:  cobra.ExactArgs(1),
+			RunE: func(cmd *cobra.Command, args []string) error {
+				extName := args[0]
+				if !strings.HasPrefix(extName, "gh-") {
+					extName = "gh-" + extName
+				}
+				if err := m.Create(extName); err != nil {
+					return err
+				}
+				if io.IsStdoutTTY() {
+					link := "https://docs.github.com/en/github-cli/github-cli/creating-github-cli-extensions"
+					cs := io.ColorScheme()
+					out := heredoc.Docf(`
+						%[1]s Created directory %[2]s
+						%[1]s Initialized git repository
+						%[1]s Set up extension scaffolding
+
+						%[2]s is ready for development
+
+						Install locally with: cd %[2]s && gh extension install .
+
+						Publish to GitHub with: gh repo create %[2]s
+
+						For more information on writing extensions: %[3]s
+					`, cs.SuccessIcon(), extName, link)
+					fmt.Fprint(io.Out, out)
+				}
+				return nil
+			},
+		},
 	)
 
 	extCmd.Hidden = true

pkg/cmd/extension/command_test.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/MakeNowJust/heredoc"
 	"github.com/cli/cli/internal/config"
 	"github.com/cli/cli/pkg/cmdutil"
 	"github.com/cli/cli/pkg/extensions"
@@ -161,6 +162,50 @@ func TestNewCmdExtension(t *testing.T) {
 			},
 			wantStdout: "gh test\tcli/gh-test\t\ngh test2\tcli/gh-test2\tUpgrade available\n",
 		},
+		{
+			name: "create extension tty",
+			args: []string{"create", "test"},
+			managerStubs: func(em *extensions.ExtensionManagerMock) func(*testing.T) {
+				em.CreateFunc = func(name string) error {
+					return nil
+				}
+				return func(t *testing.T) {
+					calls := em.CreateCalls()
+					assert.Equal(t, 1, len(calls))
+					assert.Equal(t, "gh-test", calls[0].Name)
+				}
+			},
+			isTTY: true,
+			wantStdout: heredoc.Doc(`
+				✓ Created directory gh-test
+				✓ Initialized git repository
+				✓ Set up extension scaffolding
+
+				gh-test is ready for development
+
+				Install locally with: cd gh-test && gh extension install .
+
+				Publish to GitHub with: gh repo create gh-test
+
+				For more information on writing extensions: https://docs.github.com/en/github-cli/github-cli/creating-github-cli-extensions
+			`),
+		},
+		{
+			name: "create extension notty",
+			args: []string{"create", "gh-test"},
+			managerStubs: func(em *extensions.ExtensionManagerMock) func(*testing.T) {
+				em.CreateFunc = func(name string) error {
+					return nil
+				}
+				return func(t *testing.T) {
+					calls := em.CreateCalls()
+					assert.Equal(t, 1, len(calls))
+					assert.Equal(t, "gh-test", calls[0].Name)
+				}
+			},
+			isTTY:      false,
+			wantStdout: "",
+		},
 	}
 
 	for _, tt := range tests {

pkg/cmd/extension/manager.go

@@ -13,6 +13,7 @@ import (
 	"runtime"
 	"strings"
 
+	"github.com/MakeNowJust/heredoc"
 	"github.com/cli/cli/internal/config"
 	"github.com/cli/cli/pkg/extensions"
 	"github.com/cli/cli/pkg/findsh"
@@ -249,6 +250,32 @@ func (m *Manager) installDir() string {
 	return filepath.Join(m.dataDir(), "extensions")
 }
 
+func (m *Manager) Create(name string) error {
+	exe, err := m.lookPath("git")
+	if err != nil {
+		return err
+	}
+
+	err = os.Mkdir(name, 0755)
+	if err != nil {
+		return err
+	}
+
+	initCmd := m.newCommand(exe, "init", "-b", "main", "--quiet", name)
+	err = initCmd.Run()
+	if err != nil {
+		return err
+	}
+
+	fileTmpl := heredoc.Docf(`
+		#!/bin/bash
+		echo "Hello %[1]s"
+	`, name)
+	filePath := filepath.Join(name, name)
+	err = ioutil.WriteFile(filePath, []byte(fileTmpl), 0755)
+	return err
+}
+
 func runCmds(cmds []*exec.Cmd, stdout, stderr io.Writer) error {
 	for _, cmd := range cmds {
 		cmd.Stdout = stdout

pkg/cmd/extension/manager_test.go

@@ -202,6 +202,26 @@ func TestManager_Install(t *testing.T) {
 	assert.Equal(t, "", stderr.String())
 }
 
+func TestManager_Create(t *testing.T) {
+	tempDir := t.TempDir()
+	oldWd, _ := os.Getwd()
+	assert.NoError(t, os.Chdir(tempDir))
+	t.Cleanup(func() { _ = os.Chdir(oldWd) })
+	m := newTestManager(tempDir)
+	err := m.Create("gh-test")
+	assert.NoError(t, err)
+	files, err := ioutil.ReadDir(filepath.Join(tempDir, "gh-test"))
+	assert.NoError(t, err)
+	assert.Equal(t, 1, len(files))
+	extFile := files[0]
+	assert.Equal(t, "gh-test", extFile.Name())
+	if runtime.GOOS == "windows" {
+		assert.Equal(t, os.FileMode(0666), extFile.Mode())
+	} else {
+		assert.Equal(t, os.FileMode(0755), extFile.Mode())
+	}
+}
+
 func stubExtension(path string) error {
 	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
 		return err

pkg/extensions/extension.go

@@ -21,4 +21,5 @@ type ExtensionManager interface {
 	Upgrade(name string, force bool, stdout, stderr io.Writer) error
 	Remove(name string) error
 	Dispatch(args []string, stdin io.Reader, stdout, stderr io.Writer) (bool, error)
+	Create(name string) error
 }

pkg/extensions/manager_mock.go

@@ -18,6 +18,9 @@ var _ ExtensionManager = &ExtensionManagerMock{}
 //
 // 		// make and configure a mocked ExtensionManager
 // 		mockedExtensionManager := &ExtensionManagerMock{
+// 			CreateFunc: func(name string) error {
+// 				panic("mock out the Create method")
+// 			},
 // 			DispatchFunc: func(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) (bool, error) {
 // 				panic("mock out the Dispatch method")
 // 			},
@@ -43,6 +46,9 @@ var _ ExtensionManager = &ExtensionManagerMock{}
 //
 // 	}
 type ExtensionManagerMock struct {
+	// CreateFunc mocks the Create method.
+	CreateFunc func(name string) error
+
 	// DispatchFunc mocks the Dispatch method.
 	DispatchFunc func(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) (bool, error)
 
@@ -63,6 +69,11 @@ type ExtensionManagerMock struct {
 
 	// calls tracks calls to the methods.
 	calls struct {
+		// Create holds details about calls to the Create method.
+		Create []struct {
+			// Name is the name argument value.
+			Name string
+		}
 		// Dispatch holds details about calls to the Dispatch method.
 		Dispatch []struct {
 			// Args is the args argument value.
@@ -110,6 +121,7 @@ type ExtensionManagerMock struct {
 			Stderr io.Writer
 		}
 	}
+	lockCreate       sync.RWMutex
 	lockDispatch     sync.RWMutex
 	lockInstall      sync.RWMutex
 	lockInstallLocal sync.RWMutex
@@ -118,6 +130,37 @@ type ExtensionManagerMock struct {
 	lockUpgrade      sync.RWMutex
 }
 
+// Create calls CreateFunc.
+func (mock *ExtensionManagerMock) Create(name string) error {
+	if mock.CreateFunc == nil {
+		panic("ExtensionManagerMock.CreateFunc: method is nil but ExtensionManager.Create was just called")
+	}
+	callInfo := struct {
+		Name string
+	}{
+		Name: name,
+	}
+	mock.lockCreate.Lock()
+	mock.calls.Create = append(mock.calls.Create, callInfo)
+	mock.lockCreate.Unlock()
+	return mock.CreateFunc(name)
+}
+
+// CreateCalls gets all the calls that were made to Create.
+// Check the length with:
+//     len(mockedExtensionManager.CreateCalls())
+func (mock *ExtensionManagerMock) CreateCalls() []struct {
+	Name string
+} {
+	var calls []struct {
+		Name string
+	}
+	mock.lockCreate.RLock()
+	calls = mock.calls.Create
+	mock.lockCreate.RUnlock()
+	return calls
+}
+
 // Dispatch calls DispatchFunc.
 func (mock *ExtensionManagerMock) Dispatch(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) (bool, error) {
 	if mock.DispatchFunc == nil {