encoding/json: json encoder fails for embedded non-struct fields

[gopherbot]

by tkappler:

What steps will reproduce the problem?

1. Run the following program using Go tip. Go 1, and therefore play.golang.org, will not
work since their JSON encoder ignores embedded fields in a struct.

----------------------------------------
package main

import (
    "encoding/json"
    "fmt"
)

type IntType int

type MyStruct struct {
    IntType
    Name string
}

func main() {
    var i IntType = 11
    a := MyStruct{i, "test"}

    jsonStr, err := json.Marshal(a)
    fmt.Println(string(jsonStr), err)
}
----------------------------------------


What is the expected output?

A JSON serialization of a, something like {"IntType": 11, "Name":
"test"}.


What do you see instead?

----------------------------------------
panic: reflect: NumField of non-struct type [recovered]
    panic: interface conversion: string is not error: missing method Error

goroutine 1 [running]:
----- stack segment boundary -----
encoding/json.func·002(0x101d0e90, 0x101d0100)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:220 +0x92
----- stack segment boundary -----
reflect.(*rtype).NumField(0x86878, 0xc, 0xc, 0x86878)
    /Users/thomas.kappler/software/go/src/pkg/reflect/type.go:623 +0x7e
encoding/json.typeFields(0xc200042000, 0xb7868, 0xc200042000, 0xb7868, 0x0, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:607 +0x3a9
encoding/json.cachedTypeFields(0xc200042000, 0xb7868, 0x192, 0xc200042000, 0xb7868, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:694 +0xcb
encoding/json.(*encodeState).reflectValueQuoted(0xc200068000, 0xb7868, 0xc200043400,
0x192, 0x0, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:346 +0x19b5
encoding/json.(*encodeState).reflectValue(0xc200068000, 0xb7868, 0xc200043400, 0x192)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:252 +0x48
encoding/json.(*encodeState).marshal(0xc200068000, 0xb7868, 0xc200043400, 0x0, 0x0, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:223 +0x89
encoding/json.Marshal(0xb7868, 0xc200043400, 0xcd8e8, 0x4, 0xb7868, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:117 +0x60
main.main()
    /Users/thomas.kappler/jsonEmbedded.go:19 +0x7f
----------------------------------------


Which compiler are you using (5g, 6g, 8g, gccgo)?

$ go env
GOARCH="amd64"
GOBIN=""
GOCHAR="6"
GOEXE=""
GOGCCFLAGS="-g -O2 -fPIC -m64 -pthread -fno-common"
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="EDITED/go"
GOROOT="EDITED/go"
GOTOOLDIR="EDITED/go/pkg/tool/darwin_amd64"
CGO_ENABLED="1"


Which operating system are you using?

Mac OS X 10.6.8


Which version are you using?  (run 'go version')

go version devel +697f36fec52c Fri Nov 30 20:02:30 2012 +1100


Please provide any additional information below.

[gopherbot]

Comment 1 by tkappler:

Sorry, part of my stack trace is off by three lines because I inserted some println()s
in encode.go. It should be:
----- stack segment boundary -----
reflect.(*rtype).NumField(0x86778, 0xc200043480, 0xc200042000, 0x86778)
    /Users/thomas.kappler/software/go/src/pkg/reflect/type.go:623 +0x7e
encoding/json.typeFields(0xc200042000, 0xb7768, 0xc200042000, 0xb7768, 0x0, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:604 +0x335
encoding/json.cachedTypeFields(0xc200042000, 0xb7768, 0x192, 0xc200042000, 0xb7768, ...)
    /Users/thomas.kappler/software/go/src/pkg/encoding/json/encode.go:691 +0xcb

[rsc]

Comment 3:

Labels changed: added size-m.

[rsc]

Comment 4:

Labels changed: added suggested.

[davecheney]

Comment 5:

https://golang.org/cl/6938045 fixes the double panic due to the incorrect type
assertion. It does not fix the overall issue.

[rsc]

Comment 6:

Labels changed: added priority-later, removed priority-triage.

Status changed to Accepted.

[rsc]

Comment 7:

This issue was closed by revision cdec085.

Status changed to Fixed.