Problem with multiple msgp:shim variables.

[jchv]

Consider the following:

//go:generate msgp
//msgp:shim SpecialID as:[]byte using:toBytes/fromBytes

package main

import (
	"bytes"

	"github.com/tinylib/msgp/msgp"
)

type SpecialID string
type TestObj struct{ ID1, ID2 SpecialID }

func toBytes(id SpecialID) []byte   { return []byte(string(id)) }
func fromBytes(id []byte) SpecialID { return SpecialID(string(id)) }

func main() {
	buf := bytes.Buffer{}
	test := TestObj{}

	msgp.Encode(&buf, &TestObj{ID1: "1", ID2: "2"})
	msgp.Decode(&buf, &test)

	println(test.ID1 + ":" + test.ID2)
}

The output should be 1:2, but instead... it's :2.

This seems to be a result of an interesting, but very consistent bug in the generated code:

// MarshalMsg implements msgp.Marshaler
func (z *TestObj) MarshalMsg(b []byte) (o []byte, err error) {
	o = msgp.Require(b, z.Msgsize())
	// map header, size 2
	// string "ID1"
	o = append(o, 0x82, 0xa3, 0x49, 0x44, 0x31)
	o = msgp.AppendBytes(o, toBytes(z.ID2))
	// string "ID2"
	o = append(o, 0xa3, 0x49, 0x44, 0x32)
	o = msgp.AppendBytes(o, toBytes(z.ID2))
	return
}

(Needless to say, when I noticed that IDs were missing, it took me a very long time to even realize something was wrong.)

I haven't narrowed down what is going on, I just figured I'd file a bug report after a few solid hours of trying to figure out where my bug was in the first place :)

[philhofer]

Ouch, that's a subtle one! Thanks for the bug report. #169 should fix this; let me know if you have any other issues.

Thanks!