You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: unmount.go
    path of file: ./repos/nanobox/processors/env
    
    the code of the file until where you have to start completion: package env

import (
	"path/filepath"

	"github.com/nanobox-i
    
func UnmountEngine(env *models.Env, engineDir string) error {
	// unmount the engine if it's a local directory
	if engineDir != "" {
		src := engineDir                                                // local directory
		dst := filepath.Join(provider.HostShareDir(), env.ID, "engine") // b2d "global zone"

		// unmount the env on the provider
		if err := provider.RemoveMount(src, dst); err != nil {
			display.ErrorTask()
			return util.ErrorAppend(err, "failed to cleanup old engine mount")
		}
	}
	return nil
}