omitempty doesn't work for pointer types and msgpack

[akalin-keybase]

Repro test:

package main

import (
	"testing"

	"github.com/ugorji/go/codec"
)

type V struct {
	A int  `codec:"a"`
	B *int `codec:"b,omitempty"`
	C int  `codec:"c,omitempty"`
}

func TestPacketEncode(t *testing.T) {
	var v V
	var mh codec.MsgpackHandle
	var encoded []byte
	e := codec.NewEncoderBytes(&encoded, &mh)
	err := e.Encode(v)
	if err != nil {
		t.Fatal(err)
	}

	t.Logf("Encoded to %#v", encoded)
	if encoded[0] != 0x81 {
		t.Fatalf("Expected first byte of %#v to be 0x81", encoded)
	}
}

prints:

go test .
--- FAIL: TestPacketEncode (0.00s)
	msgpack_test.go:25: Encoded to []byte{0x82, 0xa1, 0x61, 0x0, 0xa1, 0x62, 0xc0}
	msgpack_test.go:27: Expected first byte of []byte{0x82, 0xa1, 0x61, 0x0, 0xa1, 0x62, 0xc0} to be 0x81
FAIL

on master and v1.1.

I'll see if I can bisect it...

[akalin-keybase]

git bisect points to d41456c

[ugorji]

Why should the first character be 0x81?

[akalin-keybase]

Sorry for not being clear, that's the marker for a map with one element: https://github.com/msgpack/msgpack/blob/master/spec.md#map-format-family . 0x82 is the marker for a map with two elements (since B is erroneously encoded).