Use go-git for common git operations instead of calling the git

command using `os/exec`

This patch updates all the helper functions to use `go-git` library
instead of having to call `os/exec.Command`/`os/exec.CombinedOutput` in
order to clone repository, fetch tags... These changes brings more
dependencies to our `go.mod` but in exchange it simplifies the way we
interact with git repositories and improves errors handling and
readability.

Future changes will also benefit from this patch, especially
conversation webhook generator that will need to checkout multiple
version tags.

cmd/ack-generate/command/apis.go

@@ -91,7 +91,7 @@ func generateAPIs(cmd *cobra.Command, args []string) error {
 	if optOutputPath == "" {
 		optOutputPath = filepath.Join(optServicesDir, svcAlias)
 	}
-	if err := ensureSDKRepo(optCacheDir); err != nil {
+	if err := ensureSDKRepo(optCacheDir, optRefreshCache); err != nil {
 		return err
 	}
 	sdkHelper := model.NewSDKHelper(sdkDir)

cmd/ack-generate/command/common.go

@@ -14,14 +14,16 @@
 package command
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"strings"
 
 	"golang.org/x/mod/modfile"
+
+	"github.com/aws-controllers-k8s/code-generator/pkg/util"
 )
 
 const (
@@ -64,67 +66,93 @@ func isDirWriteable(fp string) bool {
 // ensureSDKRepo ensures that we have a git clone'd copy of the aws-sdk-go
 // repository, which we use model JSON files from. Upon successful return of
 // this function, the sdkDir global variable will be set to the directory where
-// the aws-sdk-go is found
-func ensureSDKRepo(cacheDir string) error {
+// the aws-sdk-go is found. It will also optionally fetch all the remote tags
+// and checkout the given tag.
+func ensureSDKRepo(
+	cacheDir string,
+	// A boolean instructing ensureSDKRepo whether to fetch the remote tags from
+	// the upstream repository
+	fetchTags bool,
+) error {
 	var err error
 	srcPath := filepath.Join(cacheDir, "src")
 	if err = os.MkdirAll(srcPath, os.ModePerm); err != nil {
 		return err
 	}
-	// clone the aws-sdk-go repository locally so we can query for API
-	// information in the models/apis/ directories
-	sdkDir, err = cloneSDKRepo(srcPath)
-	return err
-}
 
-// cloneSDKRepo git clone's the aws-sdk-go source repo into the cache and
-// returns the filepath to the clone'd repo. If the aws-sdk-go repository
-// already exists in the cache, it will checkout the current sdk-go version
-// mentionned in 'go.mod' file.
-func cloneSDKRepo(srcPath string) (string, error) {
-	sdkVersion, err := getSDKVersion()
-	if err != nil {
-		return "", err
+	// Clone repository if it doen't exist
+	sdkDir = filepath.Join(srcPath, "aws-sdk-go")
+	if _, err := os.Stat(sdkDir); os.IsNotExist(err) {
+		err = util.CloneRepository(context.Background(), sdkDir, sdkRepoURL)
+		if err != nil {
+			return fmt.Errorf("canot clone repository: %v", err)
+		}
 	}
-	clonePath := filepath.Join(srcPath, "aws-sdk-go")
-	if optRefreshCache {
-		if _, err := os.Stat(filepath.Join(clonePath, ".git")); !os.IsNotExist(err) {
-			cmd := exec.Command("git", "-C", clonePath, "fetch", "--all", "--tags")
-			if err = cmd.Run(); err != nil {
-				return "", err
-			}
-			cmd = exec.Command("git", "-C", clonePath, "checkout", "tags/"+sdkVersion)
-			return clonePath, cmd.Run()
+
+	// Fetch all tags
+	if fetchTags {
+		err = util.FetchRepositoryTags(context.Background(), sdkDir)
+		if err != nil {
+			return fmt.Errorf("cannot fetch tags: %v", err)
 		}
 	}
-	if _, err := os.Stat(clonePath); os.IsNotExist(err) {
-		cmd := exec.Command("git", "clone", "-b", sdkVersion, sdkRepoURL, clonePath)
-		return clonePath, cmd.Run()
+
+	// get sdkVersion and correct it (adds missing 'v')
+	sdkVersion, err := getSDKVersion("")
+	if err != nil {
+		return err
+	}
+	sdkVersion = correctSemanticVersion(sdkVersion)
+
+	// Now checkout the local repository.
+	repo, err := util.LoadRepository(sdkDir)
+	if err != nil {
+		return fmt.Errorf("cannot read local repository: %v", err)
+	}
+
+	err = util.CheckoutRepositoryTag(repo, sdkVersion)
+	if err != nil {
+		return fmt.Errorf("cannot checkout tag: %v", err)
 	}
-	return clonePath, nil
+
+	return err
+}
+
+// correctSemanticVersion takes a semver string and tries to append the 'v'
+// prefix if it's missing.
+func correctSemanticVersion(s string) string {
+	if strings.HasPrefix(s, "v") {
+		return s
+	}
+	return fmt.Sprintf("v%s", s)
 }
 
 // getSDKVersion returns the github.com/aws/aws-sdk-go version to use. It
-// first tries to get return version from the --aws-sdk-go-version flag, then
-// look for the service controller and local go.mod files.
-func getSDKVersion() (string, error) {
+// first tries to get the version from the --aws-sdk-go-version flag, then
+// from the ack-generate-metadata.yaml and finally look for the service
+// go.mod controller.
+func getSDKVersion(
+	//TODO(a-hilaly) Parse ack-generate-metadata.yaml and pass the aws-sdk-go
+	// version here.
+	lastGenerationVersion string,
+) (string, error) {
 	// First try to get the version from --aws-sdk-go-version flag
 	if optAWSSDKGoVersion != "" {
 		return optAWSSDKGoVersion, nil
 	}
 
+	// then, try to use last generation version (from ack-generate-metadata.yaml)
+	if lastGenerationVersion != "" {
+		return lastGenerationVersion, nil
+	}
+
 	// then, try to parse the service controller go.mod file
 	sdkVersion, err := getSDKVersionFromGoMod(filepath.Join(optOutputPath, "go.mod"))
 	if err == nil {
 		return sdkVersion, nil
 	}
 
-	// then try to parse a local go.mod
-	sdkVersion, err = getSDKVersionFromGoMod("go.mod")
-	if err != nil {
-		return "", err
-	}
-	return sdkVersion, nil
+	return "", err
 }
 
 // getSDKVersionFromGoMod parses a given go.mod file and returns

cmd/ack-generate/command/controller.go

@@ -57,7 +57,7 @@ func generateController(cmd *cobra.Command, args []string) error {
 		optOutputPath = filepath.Join(optServicesDir, svcAlias)
 	}
 
-	if err := ensureSDKRepo(optCacheDir); err != nil {
+	if err := ensureSDKRepo(optCacheDir, optRefreshCache); err != nil {
 		return err
 	}
 	sdkHelper := ackmodel.NewSDKHelper(sdkDir)

cmd/ack-generate/command/crossplane.go

@@ -50,7 +50,7 @@ func generateCrossplane(_ *cobra.Command, args []string) error {
 	if len(args) != 1 {
 		return fmt.Errorf("please specify the service alias for the AWS service API to generate")
 	}
-	if err := ensureSDKRepo(optCacheDir); err != nil {
+	if err := ensureSDKRepo(optCacheDir, optRefreshCache); err != nil {
 		return err
 	}
 	svcAlias := strings.ToLower(args[0])

cmd/ack-generate/command/olm.go

@@ -81,7 +81,7 @@ func generateOLMAssets(cmd *cobra.Command, args []string) error {
 	version := args[1]
 
 	// get the generator inputs
-	if err := ensureSDKRepo(optCacheDir); err != nil {
+	if err := ensureSDKRepo(optCacheDir, optRefreshCache); err != nil {
 		return err
 	}
 	sdkHelper := ackmodel.NewSDKHelper(sdkDir)

cmd/ack-generate/command/release.go

@@ -65,7 +65,7 @@ func generateRelease(cmd *cobra.Command, args []string) error {
 	// version supplied hasn't been used (as a Git tag) before...
 	releaseVersion := strings.ToLower(args[1])
 
-	if err := ensureSDKRepo(optCacheDir); err != nil {
+	if err := ensureSDKRepo(optCacheDir, optRefreshCache); err != nil {
 		return err
 	}
 	sdkHelper := ackmodel.NewSDKHelper(sdkDir)

go.mod

@@ -16,5 +16,6 @@ require (
 	github.com/spf13/cobra v1.1.1
 	github.com/stretchr/testify v1.7.0
 	golang.org/x/mod v0.4.1
+	gopkg.in/src-d/go-git.v4 v4.13.1
 	k8s.io/apimachinery v0.20.1
 )