Pass the root directory into the fallback command

go/cmd/gitlab-shell/main.go

@@ -26,8 +26,9 @@ func findRootDir() (string, error) {
 
 // rubyExec will never return. It either replaces the current process with a
 // Ruby interpreter, or outputs an error and kills the process.
-func execRuby(readWriter *readwriter.ReadWriter) {
-	cmd := &fallback.Command{}
+func execRuby(rootDir string, readWriter *readwriter.ReadWriter) {
+	cmd := &fallback.Command{RootDir: rootDir, Args: os.Args}
+
 	if err := cmd.Execute(readWriter); err != nil {
 		fmt.Fprintf(readWriter.ErrOut, "Failed to exec: %v\n", err)
 		os.Exit(1)
@@ -43,8 +44,8 @@ func main() {
 
 	rootDir, err := findRootDir()
 	if err != nil {
-		fmt.Fprintln(readWriter.ErrOut, "Failed to determine root directory, falling back to gitlab-shell-ruby")
-		execRuby(readWriter)
+		fmt.Fprintln(readWriter.ErrOut, "Failed to determine root directory, exiting")
+		os.Exit(1)
 	}
 
 	// Fall back to Ruby in case of problems reading the config, but issue a
@@ -52,7 +53,7 @@ func main() {
 	config, err := config.NewFromDir(rootDir)
 	if err != nil {
 		fmt.Fprintln(readWriter.ErrOut, "Failed to read config, falling back to gitlab-shell-ruby")
-		execRuby(readWriter)
+		execRuby(rootDir, readWriter)
 	}
 
 	cmd, err := command.New(os.Args, config)

go/internal/command/command.go

@@ -24,7 +24,7 @@ func New(arguments []string, config *config.Config) (Command, error) {
 		return buildCommand(args, config), nil
 	}
 
-	return &fallback.Command{}, nil
+	return &fallback.Command{RootDir: config.RootDir, Args: arguments}, nil
 }
 
 func buildCommand(args *commandargs.CommandArgs, config *config.Config) Command {

go/internal/command/fallback/fallback.go

@@ -8,14 +8,25 @@ import (
 	"gitlab.com/gitlab-org/gitlab-shell/go/internal/command/readwriter"
 )
 
-type Command struct{}
+type Command struct {
+	RootDir string
+	Args    []string
+}
 
 var (
-	binDir = filepath.Dir(os.Args[0])
+	// execFunc is overridden in tests
+	execFunc = syscall.Exec
+)
+
+const (
+	RubyProgram = "gitlab-shell-ruby"
 )
 
-func (c *Command) Execute(_ *readwriter.ReadWriter) error {
-	rubyCmd := filepath.Join(binDir, "gitlab-shell-ruby")
-	execErr := syscall.Exec(rubyCmd, os.Args, os.Environ())
-	return execErr
+func (c *Command) Execute(*readwriter.ReadWriter) error {
+	rubyCmd := filepath.Join(c.RootDir, "bin", RubyProgram)
+
+	// Ensure rubyArgs[0] is the full path to gitlab-shell-ruby
+	rubyArgs := append([]string{rubyCmd}, c.Args[1:]...)
+
+	return execFunc(rubyCmd, rubyArgs, os.Environ())
 }

go/internal/command/fallback/fallback_test.go

+package fallback
+
+import (
+	"errors"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type fakeExec struct {
+	OldExec func(string, []string, []string) error
+	Error   error
+	Called  bool
+
+	Filename string
+	Args     []string
+	Env      []string
+}
+
+var (
+	fakeArgs = []string{"./test", "foo", "bar"}
+)
+
+func (f *fakeExec) Exec(filename string, args []string, env []string) error {
+	f.Called = true
+
+	f.Filename = filename
+	f.Args = args
+	f.Env = env
+
+	return f.Error
+}
+
+func (f *fakeExec) Setup() {
+	f.OldExec = execFunc
+	execFunc = f.Exec
+}
+
+func (f *fakeExec) Cleanup() {
+	execFunc = f.OldExec
+}
+
+func TestExecuteExecsCommandSuccesfully(t *testing.T) {
+	cmd := &Command{RootDir: "/tmp", Args: fakeArgs}
+
+	// Override the exec func
+	fake := &fakeExec{}
+	fake.Setup()
+	defer fake.Cleanup()
+
+	require.NoError(t, cmd.Execute(nil))
+	require.True(t, fake.Called)
+	require.Equal(t, fake.Filename, "/tmp/bin/gitlab-shell-ruby")
+	require.Equal(t, fake.Args, []string{"/tmp/bin/gitlab-shell-ruby", "foo", "bar"})
+	require.Equal(t, fake.Env, os.Environ())
+}
+
+func TestExecuteExecsCommandOnError(t *testing.T) {
+	cmd := &Command{RootDir: "/test", Args: fakeArgs}
+
+	// Override the exec func
+	fake := &fakeExec{Error: errors.New("Test error")}
+	fake.Setup()
+	defer fake.Cleanup()
+
+	require.Error(t, cmd.Execute(nil))
+	require.True(t, fake.Called)
+}
+
+func TestExecuteGivenNonexistentCommand(t *testing.T) {
+	cmd := &Command{RootDir: "/tmp/does/not/exist", Args: fakeArgs}
+
+	require.Error(t, cmd.Execute(nil))
+}