> AFK right now, but files opened with os.Open will be automatically closed once all its references have been collected.

No, they're not. The idiomatic usage is to defer a Close() call after checking that Open succeeded, like so:

  file, err := os.Open("/etc/hostname")
  if err != nil {
    doSomethingWith(err)
  }
  defer file.Close()
  doSomethingWith(file)

But you'd be forgiven for not knowing that: To my own surprise, I could not find the need for this idiom explained in the package documentation for os.Open, though you can see it in action throughout the std implementation. For example: https://cs.opensource.google/go/go/+/refs/tags/go1.20.4:src/...