os/dir: File.Readdir claims it will return an error on empty slice, but doesn't

[euank]

The current doc comment for File.Readdir here states that when n > 0, the error value will be populated if no FileInfo is returned. The reproduction I linked below clearly shows this isn't always the case, at least with the dir_unix.go implementation of it here.

It is trivial to reproduce this using the following example program: https://gist.github.com/euank/72cc2f1d13630eecd5459d8fe68e60b6

Should the documentation be changed, or should the implementation be fixed to error correctly if the implementation-specific method did not behave as the documentation suggests it should?
I'd be happy to submit a patch for this either way.

What version of Go are you using (go version)?

go version devel +e6f9f39 Mon Aug 29 18:25:33 2016 +0000 linux/amd64

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

amd64, linux

What did you do?

# Download the repro from https://gist.github.com/euank/72cc2f1d13630eecd5459d8fe68e60b6
$ go run readdir_bug.go | grep "this is a bug"
Observed err=<nil> and files=[]; this is a bug

[gopherbot]

CL https://golang.org/cl/28056 mentions this issue.