don't change GIT_SSH_COMMAND if there's no keyfile

The reason for setupGitEnv is to add a `-i keyfile` argument to
GIT_SSH_COMMAND. If there is no keyfile, we do not need to modify the
environment at all.

get_git.go

@@ -302,6 +302,11 @@ func findRemoteDefaultBranch(ctx context.Context, u *url.URL) string {
 // setupGitEnv sets up the environment for the given command. This is used to
 // pass configuration data to git and ssh and enables advanced cloning methods.
 func setupGitEnv(cmd *exec.Cmd, sshKeyFile string) {
+	// If there's no sshKeyFile argument to deal with, we can skip this
+	// entirely.
+	if sshKeyFile == "" {
+		return
+	}
 	const gitSSHCommand = "GIT_SSH_COMMAND="
 	var sshCmd []string
 
@@ -323,14 +328,12 @@ func setupGitEnv(cmd *exec.Cmd, sshKeyFile string) {
 		sshCmd = []string{gitSSHCommand + "ssh"}
 	}
 
-	if sshKeyFile != "" {
-		// We have an SSH key temp file configured, tell ssh about this.
-		if runtime.GOOS == "windows" {
-			sshKeyFile = strings.Replace(sshKeyFile, `\`, `/`, -1)
-		}
-		sshCmd = append(sshCmd, "-i", sshKeyFile)
-		env = append(env, strings.Join(sshCmd, " "))
+	// We have an SSH key temp file configured, tell ssh about this.
+	if runtime.GOOS == "windows" {
+		sshKeyFile = strings.Replace(sshKeyFile, `\`, `/`, -1)
 	}
+	sshCmd = append(sshCmd, "-i", sshKeyFile)
+	env = append(env, strings.Join(sshCmd, " "))
 
 	cmd.Env = env
 }

get_git_test.go

@@ -699,6 +699,29 @@ func TestGitGetter_setupGitEnvWithExisting_sshKey(t *testing.T) {
 	}
 }
 
+func TestGitGetter_setupGitEnvWithNoKeyFile(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skipf("skipping on windows since the test requires sh")
+		return
+	}
+
+	// start with an existing ssh command configuration
+	os.Setenv("GIT_SSH_COMMAND", "ssh -o StrictHostKeyChecking=no")
+	defer os.Setenv("GIT_SSH_COMMAND", "")
+
+	cmd := exec.Command("/bin/sh", "-c", "echo $GIT_SSH_COMMAND")
+	setupGitEnv(cmd, "")
+	out, err := cmd.Output()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	actual := strings.TrimSpace(string(out))
+	if actual != "ssh -o StrictHostKeyChecking=no" {
+		t.Fatalf("unexpected GIT_SSH_COMMAND: %q", actual)
+	}
+}
+
 func TestGitGetter_subdirectory_symlink(t *testing.T) {
 	if !testHasGit {
 		t.Skip("git not found, skipping")