JSON encoder fails for embedded non-struct fields

[Thomas Kappler]

If I define a type that's not a struct, like "type foo int", and embed this type into a struct, the JSON encoder panics on it. This might be a bug. If not, please educate me about what I'm doing wrong!

Here's a minimal example:

---------------------------
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)
}
---------------------------

Running this, I get

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


Looking at encoding/json/encode.go line 604, function typeFields, it calls NumField() without checking whether f.typ is actually a struct.


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

$ 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"

[minux]

please file an issue.

--
 
 

[Thomas Kappler]

Thanks, filed http://code.google.com/p/go/issues/detail?id=4474.

[Rémy Oudompheng]

On 2013/2/22 <frederic...@gmail.com> wrote:
> I have a similar problem, though without panic.
> http://play.golang.org/p/ihWKpTZ8mq
>
> Will the fix also address this or should I open a new issue?

The problme is not similar, your example is about embedded structs
(issues 3069, 4632).
It's fixed for Go 1.1 and your program will print:

{"Source":54,"Date":"2013-02-22T13:35:12.000679436+01:00"}

for example.

Rémy.

[Frédéric Donckels]

> The problme is not similar, your example is about embedded structs
> (issues 3069, 4632).
> It's fixed for Go 1.1 and your program will print:
>
> {"Source":54,"Date":"2013-02-22T13:35:12.000679436+01:00"}
>

Perfect! I can't wait for Go 1.1

Frédéric