code: func FileDescriptorName(protoFile string, importDirs []string) string {
  	isAbs := path.IsAbs(protoFile)
  	for _, imp := range importDirs {
  		// Handle import dirs of "." - the FileDescriptorProtos don't have the "./" prefix.
  		if imp == "." && !isAbs {
  			if strings.HasPrefix(protoFile, "./") {
  				return protoFile[2:]
  			}
  			return protoFile
  		}
  		if strings.HasPrefix(protoFile, imp) {
  			name := protoFile[len(imp):]
  			if strings.HasPrefix(name, "/") && imp != "/" {
  				return name[1:]
  			}
  			return name
  		}
  	}
  	panic(fmt.Sprintf("Unable to find import dir for %q", protoFile))
  }
docs: // FileDescriptorName computes the import-dir-relative Name that the
  // FileDescriptor for a full filename will have.