Embedded structs' fields are not omitted

[khpeek]

Unlike Go's encoding/json, it would appear that go-plist still marshals the fields of embedded structs even if those structs are nil and the omitempty tag is specified. Consider the following example program:

package main

import (
    "fmt"
    "log"

    "howett.net/plist"
)

type Location struct {
    Name        string
    Type        string
    *Restaurant `plist:",omitempty"`
    *Store      `plist:",omitempty"`
}

type Restaurant struct {
    Menu string
}

type Store struct {
    Merchandise string
}

func main() {
    location := Location{
        Name: "Taqueria Cancun",
        Type: "Restaurant",
        Restaurant: &Restaurant{
            Menu: "Tacos",
        },
    }

    locationPlist, err := plist.MarshalIndent(&location, plist.XMLFormat, "\t")
    if err != nil {
        log.Fatalf("marshal location: %v", err)
    }

    fmt.Println(string(locationPlist))
}

The resulting property list is

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Menu</key>
        <string>Tacos</string>
        <key>Merchandise</key>
        <string/>
        <key>Name</key>
        <string>Taqueria Cancun</string>
        <key>Type</key>
        <string>Restaurant</string>
    </dict>
</plist>

This plist representation contains an empty Merchandise string which is not pertinent to a Restaurant and which I'd like to omit. The encoding/json library does this as seen from the example below:

package main

import (
    "encoding/json"
    "fmt"
    "log"
)

type Location struct {
    Name string
    Type string
    *Restaurant
    *Store
}

type Restaurant struct {
    Menu string
}

type Store struct {
    Merchandise string
}

func main() {
    location := Location{
        Name: "Taqueria Cancun",
        Type: "Restaurant",
        Restaurant: &Restaurant{
            Menu: "Tacos",
        },
    }

    locationJSON, err := json.Marshal(&location)
    if err != nil {
        log.Fatalf("marshal location: %v", err)
    }

    fmt.Println(string(locationJSON))
}

Running this (and piping the output to jq) results in

{
  "Name": "Taqueria Cancun",
  "Type": "Restaurant",
  "Menu": "Tacos"
}

where the Merchandise key is absent. Should the go-plist library not also have this behavior?

[khpeek]

One way to work around this (which is probably better pattern in general) is to embed the Location struct into the Restaurant and Store structs rather than vice versa:

package main

import (
    "fmt"
    "log"

    "howett.net/plist"
)

type Location struct {
    Name string
    Type string
}

type Restaurant struct {
    Location
    Menu string
}

type Store struct {
    Location
    Merchandise string
}

func main() {
    restaurant := Restaurant{
        Location: Location{
            Name: "Taqueria Cancun",
            Type: "Restaurant",
        },
        Menu: "Tacos",
    }

    locationPlist, err := plist.MarshalIndent(&restaurant, plist.XMLFormat, "\t")
    if err != nil {
        log.Fatalf("marshal location: %v", err)
    }

    fmt.Println(string(locationPlist))
}

This results in the desired output,

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Menu</key>
        <string>Tacos</string>
        <key>Name</key>
        <string>Taqueria Cancun</string>
        <key>Type</key>
        <string>Restaurant</string>
    </dict>
</plist>

However, my point still stands that go-plist's behavior deviates from that of encoding/json in this regard.

[DHowett]

Thanks for the report, and comprehensive investigation! I'm a bit behind on my personal repositories, but I'll try to get to this this week. You're right - this should work like encoding/json. There's a chance that this behavior has changed over time and I missed it, or I never mimicked encoding/json properly. :smile: