code: func (b *BuildArgs) WarnOnUnusedBuildArgs(out io.Writer) {
  	var leftoverArgs []string
  	for arg := range b.argsFromOptions {
  		_, isReferenced := b.referencedArgs[arg]
  		_, isBuiltin := builtinAllowedBuildArgs[arg]
  		if !isBuiltin && !isReferenced {
  			leftoverArgs = append(leftoverArgs, arg)
  		}
  	}
  	if len(leftoverArgs) > 0 {
  		fmt.Fprintf(out, "[Warning] One or more build-args %v were not consumed\n", leftoverArgs)
  	}
  }
docs: // WarnOnUnusedBuildArgs checks if there are any leftover build-args that were
  // passed but not consumed during build. Print a warning, if there are any.