json.Marshal returns {} for a struct when struct vars start with lowercase

[gopherbot]

by hendrik.demolder:

What steps will reproduce the problem?:

package main 
import (
        "json"
        "fmt" 
) 
type Message struct { 
        test string
        test2 string
}


func main() {  
        var m  = Message{"t1", "t22"}
        output, _ := json.Marshal(m) 
        fmt.Println(string(output))
} 




What is the expected output?:

{"Test":"t1","Test2":"t22"}


What do you see instead?:
{}

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

Which operating system are you using?
linux/Fedora 

Which revision are you using?  (hg identify)
d5785050f61d (release-branch.r59) release/release.r59

Additional remarks:

By changing Message to:

type Message struct { 
        Test string
        Test2 string
}

It works correclty: {"Test":"t1","Test2":"t22"}

[rsc]

Comment 1:

Because Unmarshal cannot write to lower case fields,
Marshal ignores them for symmetry.  They are only
exposed by reflect for easier debugging with fmt.Print.
If you need a field with a lower-case name in the
json output you can write
type Message struct {
    Test string  `json:"test"`
}
Russ

Status changed to WorkingAsIntended.