Comment 1:

Labels changed: added repo-main, release-go1.3.

Comment 2:

line 19:
bytes := make([]byte, 0, 1048576)
is wrong. the slice provided to Stack has length of 0, so the only number Stack
could return 0.

Status changed to WorkingAsIntended.

Comment 3 by james.jdunne:

That's C semantics, not  Go semantics. You have an allocated buffer with plenty
capacity. Length should be zero. The Stack function should fill the buffer up to
capacity at most, not its length. This would remove the need for the nonstandard int
return value representing the new length of the buffer.

Comment 4:

It is Go semantics. see also io.Reader.
API should generally not change len of a slice passed in (for example,
consider that, before the introduction of three index slides, what if
you have a custom []byte allocator that allocates from a big []byte?
Writing past the length might corrupt the memory of others unrelated
byte slices).