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
    GoMod     string        `json:",omitempty"` // path to go.mod file describing module, if any
    GoVersion string        `json:",omitempty"` // go version used in module
    Error     *ModuleError  `json:",omitempty"` // error loading module
}