go version go1.19.1 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

amd64, intel i7

If you use mmap to map a file of 0 length, any future usage of the mapped file results in an error mmap: closed

The offending code is:

	size := fi.Size()
	if size == 0 {
		return &ReaderAt{}, nil
	}

in mmap_unix.go, in func Open(filename string) (*ReaderAt, error) - lines 92-95.

I don't think this is correct or expected behavior. You should be able to mmap a zero length file and use it.