code: func (p *Plugin) Open(fn *function.Function) error {
  	if fn.Runtime != "" {
  		return nil
  	}
  
  	fn.Log.Debug("inferring runtime")
  
  	for name, runtime := range p.Files {
  		if _, err := os.Stat(filepath.Join(fn.Path, name)); err == nil {
  			fn.Log.WithField("runtime", runtime).Debug("inferred runtime")
  			fn.Runtime = runtime
  			return nil
  		}
  	}
  
  	return nil
  }
docs: // Open checks for files in the function directory to infer its runtime.