type ModuleError struct {
	Err string // error text
}

type ModulePublic struct {
	Path     string        `json:",omitempty"` // module path
	Version  string        `json:",omitempty"` // module version
	Versions []string      `json:",omitempty"` // available module versions
	Replace  *ModulePublic `json:",omitempty"` // replaced by this module
	Time     *time.Time    `json:",omitempty"` // time version was created
	Update   *ModulePublic `json:",omitempty"` // available update (with -u)
	Main     bool          `json:",omitempty"` // is this the main module?
	Indirect bool          `json:",omitempty"` // module is only indirectly needed by main module
	Dir      string        `json:",omitempty"` // directory holding local copy of files, if any
	Error    *ModuleError  `json:",omitempty"` // error loading module
}