for _, m := range ms {
		if mainModulePaths[m.Path] {
			base.Errorf("go: module %s appears multiple times in workspace", m.Path)
		}
		mainModulePaths[m.Path] = true
	}
	replacedByWorkFile := make(map[string]bool)
	replacements := make(map[module.Version]module.Version)
	for _, r := range workFileReplaces {
		if mainModulePaths[r.Old.Path] && r.Old.Version == "" {