Add support for cloning repositories (#544)

## Changes
Adds support for cloning public and private github repositories for
databricks templates

## Tests
Integration tests

internal/git_clone_test.go

@@ -0,0 +1,63 @@
+package internal
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/databricks/cli/libs/git"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAccGitClone(t *testing.T) {
+	t.Log(GetEnvOrSkipTest(t, "CLOUD_ENV"))
+
+	tmpDir := t.TempDir()
+	ctx := context.Background()
+	var err error
+
+	err = git.Clone(ctx, "https://github.com/databricks/databricks-empty-ide-project.git", "", tmpDir)
+	assert.NoError(t, err)
+
+	// assert repo content
+	assert.NoError(t, err)
+	b, err := os.ReadFile(filepath.Join(tmpDir, "README-IDE.md"))
+	assert.NoError(t, err)
+	assert.Contains(t, string(b), "This folder contains a project that was synchronized from an IDE.")
+
+	// assert current branch is ide, ie default for the repo
+	b, err = os.ReadFile(filepath.Join(tmpDir, ".git/HEAD"))
+	assert.NoError(t, err)
+	assert.Contains(t, string(b), "ide")
+}
+
+func TestAccGitCloneWithOnlyRepoNameOnAlternateBranch(t *testing.T) {
+	t.Log(GetEnvOrSkipTest(t, "CLOUD_ENV"))
+
+	tmpDir := t.TempDir()
+	ctx := context.Background()
+	var err error
+
+	err = git.Clone(ctx, "notebook-best-practices", "dais-2022", tmpDir)
+
+	// assert on repo content
+	assert.NoError(t, err)
+	b, err := os.ReadFile(filepath.Join(tmpDir, "README.md"))
+	assert.NoError(t, err)
+	assert.Contains(t, string(b), "Software engineering best practices for Databricks notebooks")
+
+	// assert current branch is main, ie default for the repo
+	b, err = os.ReadFile(filepath.Join(tmpDir, ".git/HEAD"))
+	assert.NoError(t, err)
+	assert.Contains(t, string(b), "dais-2022")
+}
+
+func TestAccGitCloneRepositoryDoesNotExist(t *testing.T) {
+	t.Log(GetEnvOrSkipTest(t, "CLOUD_ENV"))
+
+	tmpDir := t.TempDir()
+
+	err := git.Clone(context.Background(), "doesnot-exist", "", tmpDir)
+	assert.Contains(t, err.Error(), `repository 'https://github.com/databricks/doesnot-exist/' not found`)
+}

libs/git/clone.go

@@ -0,0 +1,72 @@
+package git
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"regexp"
+	"strings"
+)
+
+// source: https://stackoverflow.com/questions/59081778/rules-for-special-characters-in-github-repository-name
+var githubRepoRegex = regexp.MustCompile(`^[\w-\.]+$`)
+
+const githubUrl = "https://github.com"
+const databricksOrg = "databricks"
+
+type cloneOptions struct {
+	// Branch or tag to clone
+	Reference string
+
+	// URL for the repository
+	RepositoryUrl string
+
+	// Local path to clone repository at
+	TargetPath string
+}
+
+func (opts cloneOptions) args() []string {
+	args := []string{"clone", opts.RepositoryUrl, opts.TargetPath, "--depth=1", "--no-tags"}
+	if opts.Reference != "" {
+		args = append(args, "--branch", opts.Reference)
+	}
+	return args
+}
+
+func Clone(ctx context.Context, url, reference, targetPath string) error {
+	// We assume only the repository name has been if input does not contain any
+	// `/` characters and the url is only made up of alphanumeric characters and
+	// ".", "_" and "-". This repository is resolved again databricks github account.
+	fullUrl := url
+	if githubRepoRegex.MatchString(url) {
+		fullUrl = strings.Join([]string{githubUrl, databricksOrg, url}, "/")
+	}
+
+	opts := cloneOptions{
+		Reference:     reference,
+		RepositoryUrl: fullUrl,
+		TargetPath:    targetPath,
+	}
+
+	cmd := exec.CommandContext(ctx, "git", opts.args()...)
+	var cmdErr bytes.Buffer
+	cmd.Stderr = &cmdErr
+
+	// start git clone
+	err := cmd.Start()
+	if errors.Is(err, exec.ErrNotFound) {
+		return fmt.Errorf("please install git CLI to clone a repository: %w", err)
+	}
+	if err != nil {
+		return err
+	}
+
+	// wait for git clone to complete
+	err = cmd.Wait()
+	if err != nil {
+		return fmt.Errorf("git clone failed: %w. %s", err, cmdErr.String())
+	}
+	return nil
+}

libs/git/clone_test.go

@@ -0,0 +1,34 @@
+package git
+
+import (
+	"context"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGitCloneArgs(t *testing.T) {
+	// case: No branch / tag specified. In this case git clones the default branch
+	assert.Equal(t, []string{"clone", "abc", "/def", "--depth=1", "--no-tags"}, cloneOptions{
+		Reference:     "",
+		RepositoryUrl: "abc",
+		TargetPath:    "/def",
+	}.args())
+
+	// case: A branch is specified.
+	assert.Equal(t, []string{"clone", "abc", "/def", "--depth=1", "--no-tags", "--branch", "my-branch"}, cloneOptions{
+		Reference:     "my-branch",
+		RepositoryUrl: "abc",
+		TargetPath:    "/def",
+	}.args())
+}
+
+func TestGitCloneWithGitNotFound(t *testing.T) {
+	// We set $PATH here so the git CLI cannot be found by the clone function
+	t.Setenv("PATH", "")
+	tmpDir := t.TempDir()
+
+	err := Clone(context.Background(), "abc", "", tmpDir)
+	assert.ErrorIs(t, err, exec.ErrNotFound)
+}