os: document form of returned errors

[bradfitz]

As a newcomer to Go, I remember struggling with trying to find os.ENOENT, buried in a
PathError, buried in an os.Error.  This keeps coming up on the list too.

The docs don't even say what type of errors Open or Stat might return:

http://golang.org/pkg/os/#File.Open
http://golang.org/pkg/os/#File.Stat

(I remember first going on a mission to find a pretty printing function, eventually
finding fmt %T and %#v)

It might be worth calling out at least os.PathError there, and perhaps something like
"If the file doesn't exist, the returned error will be of type *os.PathError, with
a PathError.Error value of ENOENT".

[rsc]

Comment 1:

Owner changed to @rsc.

Status changed to Accepted.

[rsc]

Comment 2:

Labels changed: added priority-later.

[rsc]

Comment 3:

Labels changed: added priority-go1.

[hanwen]

Comment 4:

For writing go-fuse I only need the errno error, since that is the only I can pass back.
I ended up writing a function that tries to unpack the various errors and extract the
error number.  It's fragile though, since it depends on what error types the os package
creates.  
I would very much welcome something that converts os errors to either an errno int
(preferred) or a syscall.Errno error.

[bradfitz]

Comment 5:

Re comment #4, that's going the wrong direction, from portable to non-portable.

[robpike]

Comment 6:

Owner changed to builder@golang.org.

[rsc]

Comment 8:

Labels changed: added go1-must.

[robpike]

Comment 9:

This issue was closed by revision be0f6fe.

Status changed to Fixed.