encoding/asn1: cannot unmarshal SET if its fields have different ordering

[hirochachacha]

Please answer these questions before submitting your issue. Thanks!

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

package main

import (
	"encoding/asn1"
	"fmt"
)

type A struct {
	Name string
	Int  int
}

type B struct {
	Int  int
	Name string
}

func main() {
	bs, err := asn1.Marshal(A{Name: "foo", Int: 5})
	if err != nil {
		panic(err)
	}

	bs[0] = asn1.TagSet | 0x20

	var b B

	rest, err := asn1.UnmarshalWithParams(bs, &b, "set")
	if err != nil {
		panic(err)
	}
	if len(rest) != 0 {
		panic("invalid length")
	}

	fmt.Println(b)
}

What did you expect to see?

{5 foo}

What did you see instead?

panic: asn1: structure error: tags don't match (2 vs {class:0 tag:19 length:3 isCompound:false}) {optional:false explicit:false application:false defaultValue: tag: stringType:0 timeType:0 set:false omitEmpty:false} int @2

goroutine 1 [running]:
main.main()
/Users/hiro/set.go:42 +0x24a
exit status 2

Does this issue reproduce with the latest release (go1.8)?

yes

System details

go version devel +5cadc91b3c Tue Apr 4 02:40:11 2017 +0000 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/hiro/.go"
GORACE=""
GOROOT="/Users/hiro/go"
GOTOOLDIR="/Users/hiro/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/wq/dwn8hs0x7njbzty9f68y61700000gn/T/go-build019140017=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOROOT/bin/go version: go version devel +5cadc91b3c Tue Apr 4 02:40:11 2017 +0000 darwin/amd64
GOROOT/bin/go tool compile -V: compile version devel +5cadc91b3c Tue Apr 4 02:40:11 2017 +0000 X:framepointer
uname -v: Darwin Kernel Version 16.5.0: Fri Mar  3 16:52:33 PST 2017; root:xnu-3789.51.2~3/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.12.4
BuildVersion:	16E195
lldb --version: lldb-370.0.37
  Swift-3.1
gdb --version: GNU gdb (GDB) 7.12.1

[bradfitz]

I'm not sure whether this is a bug, but even if it is, I think encoding/asn1 is on life support and mostly frozen. It exists in the standard library just to serve crypto/tls via crypto/x509.

I'll let @agl decide.