fix(internal/gapicgen): filter out internal directory changes (#4085)

- Filter out internal dir changes since they do not need a module
  update.
- Remove unneeded param from method
- Log extra details when a excuting a command yields an error

internal/gapicgen/cmd/genbot/update.go

@@ -30,7 +30,7 @@ func updateGocloudPR(ctx context.Context, githubClient *git.GithubClient, pr *gi
 	}
 
 	// Checkout PR and update go.mod
-	if err := githubClient.UpdateGocloudGoMod(pr); err != nil {
+	if err := githubClient.UpdateGocloudGoMod(); err != nil {
 		return err
 	}
 

internal/gapicgen/execv/command.go

@@ -41,8 +41,26 @@ func Command(name string, arg ...string) *CmdWrapper {
 
 // Run a command.
 func (c *CmdWrapper) Run() error {
-	log.Printf("[%s] >>>> %v <<<<", c.Dir, strings.Join(c.Args, " ")) // NOTE: we have some multi-line commands, make it clear where the command starts and ends
-	return c.Cmd.Run()
+	log.Printf("[%s] >>>> %v <<<<", c.Dir, strings.Join(c.Args, " "))
+	err := c.Cmd.Run()
+	if err != nil {
+		if ee, ok := err.(*exec.ExitError); ok {
+			log.Println(string(ee.Stderr))
+		}
+	}
+	return err
+}
+
+// Output a command.
+func (c *CmdWrapper) Output() ([]byte, error) {
+	log.Printf("[%s] >>>> %v <<<<", c.Dir, strings.Join(c.Args, " "))
+	b, err := c.Cmd.Output()
+	if err != nil {
+		if ee, ok := err.(*exec.ExitError); ok {
+			log.Println(string(ee.Stderr))
+		}
+	}
+	return b, err
 }
 
 // ForEachMod runs the given function with the directory of

internal/gapicgen/git/github.go

@@ -15,7 +15,6 @@
 package git
 
 import (
-	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -336,7 +335,7 @@ func (gc *GithubClient) MarkPRReadyForReview(ctx context.Context, repo string, n
 
 // UpdateGocloudGoMod updates the go.mod to include latest version of genproto
 // for the given gocloud ref.
-func (gc *GithubClient) UpdateGocloudGoMod(pr *PullRequest) error {
+func (gc *GithubClient) UpdateGocloudGoMod() error {
 	tmpDir, err := ioutil.TempDir("", "finalize-github-pr")
 	if err != nil {
 		return err
@@ -374,26 +373,25 @@ git checkout $BRANCH_NAME
 
 func updateDeps(tmpDir string) error {
 	// Find directories that had code changes.
-	out := bytes.NewBuffer(nil)
 	c := execv.Command("git", "diff", "--name-only", "HEAD", "HEAD~1")
-	c.Stdout = out
 	c.Dir = tmpDir
-	if err := c.Run(); err != nil {
+	out, err := c.Output()
+	if err != nil {
 		return err
 	}
-	files := strings.Split(out.String(), "\n")
+	files := strings.Split(string(out), "\n")
 	dirs := map[string]bool{}
 	for _, file := range files {
+		if strings.HasPrefix(file, "internal") {
+			continue
+		}
 		dir := filepath.Dir(file)
 		dirs[filepath.Join(tmpDir, dir)] = true
 	}
 
 	// Find which modules had code changes.
 	updatedModDirs := map[string]bool{}
-	errWriter := bytes.NewBuffer(nil)
 	for dir := range dirs {
-		out.Reset()
-		errWriter.Reset()
 		modDir, err := gocmd.ListModDirName(dir)
 		if err != nil {
 			if errors.Is(err, gocmd.ErrBuildConstraint) {