code: func ApplyToSource(fileExtension string,
  	ignoredSubdirectories []string,
  	commandParts ...string) error {
  	if len(commandParts) <= 0 {
  		return errors.New("applyToSource requires a command to apply to source files")
  	}
  	eligibleSourceFiles, eligibleSourceFilesErr := sourceFilesOfType(fileExtension, ignoredSubdirectories)
  	if eligibleSourceFilesErr != nil {
  		return eligibleSourceFilesErr
  	}
  
  	Log(header)
  	Log("Applying `%s` to %d `*.%s` source files", commandParts[0], len(eligibleSourceFiles), fileExtension)
  	Log(header)
  
  	commandArgs := []string{}
  	if len(commandParts) > 1 {
  		commandArgs = append(commandArgs, commandParts[1:]...)
  	}
  	for _, eachFile := range eligibleSourceFiles {
  		applyArgs := append(commandArgs, eachFile)
  		applyErr := sh.Run(commandParts[0], applyArgs...)
  		if applyErr != nil {
  			return applyErr
  		}
  	}
  	return nil
  }
docs: // ApplyToSource is a mage compatible function that applies a
  // command to your source tree