func runInDir()

in mockgen/reflect.go [134:180]
40 lines of code
9 McCabe index (conditional complexity)

func runInDir(program []byte, dir string) (*model.Package, error) {
	// We use TempDir instead of TempFile so we can control the filename.
	tmpDir, err := ioutil.TempDir(dir, "gomock_reflect_")
	if err != nil {
		return nil, err
	}
	defer func() {
		if err := os.RemoveAll(tmpDir); err != nil {
			log.Printf("failed to remove temp directory: %s", err)
		}
	}()
	const progSource = "prog.go"
	var progBinary = "prog.bin"
	if runtime.GOOS == "windows" {
		// Windows won't execute a program unless it has a ".exe" suffix.
		progBinary += ".exe"
	}

	if err := ioutil.WriteFile(filepath.Join(tmpDir, progSource), program, 0600); err != nil {
		return nil, err
	}

	cmdArgs := []string{}
	cmdArgs = append(cmdArgs, "build")
	if *buildFlags != "" {
		cmdArgs = append(cmdArgs, strings.Split(*buildFlags, " ")...)
	}
	cmdArgs = append(cmdArgs, "-o", progBinary, progSource)

	// Build the program.
	buf := bytes.NewBuffer(nil)
	cmd := exec.Command("go", cmdArgs...)
	cmd.Dir = tmpDir
	cmd.Stdout = os.Stdout
	cmd.Stderr = io.MultiWriter(os.Stderr, buf)
	if err := cmd.Run(); err != nil {
		sErr := buf.String()
		if strings.Contains(sErr, `cannot find package "."`) &&
			strings.Contains(sErr, "github.com/golang/mock/mockgen/model") {
			fmt.Fprint(os.Stderr, "Please reference the steps in the README to fix this error:\n\thttps://github.com/golang/mock#reflect-vendoring-error.\n")
			return nil, err
		}
		return nil, err
	}

	return run(filepath.Join(tmpDir, progBinary))
}