Print stderr when git fails (#15)

Author: bretwalker

cmd/get_targets.go

@@ -60,8 +60,8 @@ $ bazel-differ get-targets -w path/to/workspace -b $(which bazel) -s START_HASH
 
 func getHashes(revision string, gitClient internal.GitClient, cacheManager cache.HashCacheManager,
 	targetHasher internal.TargetHashingClient) map[string]string {
-	err := gitClient.Checkout(revision)
-	ExitIfError(err, fmt.Sprintf("Unable to checkout revision: %s", revision))
+	output, err := gitClient.Checkout(revision)
+	ExitIfError(err, fmt.Sprintf("Unable to checkout revision: %s. %s", revision, output))
 
 	var seedfilePaths = make(map[string]bool)
 	if SeedFilepaths != "" {

internal/git_client.go

@@ -5,7 +5,7 @@ import (
 )
 
 type GitClient interface {
-	Checkout(hash string) error
+	Checkout(hash string) (string, error)
 }
 
 type gitClient struct {
@@ -18,8 +18,8 @@ func NewGitClient(dir string) GitClient {
 	}
 }
 
-func (g gitClient) Checkout(hash string) error {
+func (g gitClient) Checkout(hash string) (string, error) {
 	cmd := exec.Command("git", "-C", g.dir, "checkout", hash, "--quiet")
-	_, err := cmd.Output()
-	return err
+	output, err := cmd.CombinedOutput()
+	return string(output), err
 }