JSON package doesn't roundtrip null values

[spahnke]

Context

Odin:    dev-2025-02-nightly:584fdc0
OS:      macOS Sequoia 15.3.1 (build 24D70, kernel 24.3.0)
CPU:     Apple M4
RAM:     24576 MiB
Backend: LLVM 18.1.8

I needed a small tool to combine several JSON files into one that I wanted to try Odin for, but got met with a marshaling error "Unsupported type". This is because the original files contain objects with fields of value null that need to be roundtripped (see code example below). I suspect this is because the parsed value is a json.Null union variant, especially because using nil works, but directly using json.Null {} does not. The unsupported type error gets raised here

Odin/core/encoding/json/marshal.odin

Line 178 in f390598

case runtime.Type_Info_Pointer:

Let me know should there be a setting I haven't found.

Expected Behavior

null values can be roundtripped when first parsed and then marshaled.

Current Behavior

Unsupported type error.

Example

The original roundtripping code I wanted to write is in the last example block. The first 2 showcase the error when manually building a JSON object where nil works but json.Null {} doesn't.

package main

import "core:fmt"
import "core:encoding/json"

main :: proc() {
	// works
	{
		parsed: json.Object
		parsed["id"] = 234
		parsed["title"] = "asdf"
		parsed["runtime"] = 56.9
		parsed["creator"] = nil
		bytes, err := json.marshal(parsed)
		assert(err == nil)
		str := cast(string)bytes
		fmt.println(str)
	}

	// does not work
	{
		parsed: json.Object
		parsed["id"] = 234
		parsed["title"] = "asdf"
		parsed["runtime"] = 56.9
		parsed["creator"] = json.Null {} // this is what you get when parsing null
		bytes, err := json.marshal(parsed)
		assert(err == nil)
		str := cast(string)bytes
		fmt.println(str)
	}

	// does not work - original roundtripping code I wanted to write
	{
		content := `
{
	"id": 234,
	"title": "asdf",
	"runtime": 56.9,
	"creator": null
}
`
		parsed, _ := json.parse(transmute([]u8)content)
		bytes, err := json.marshal(parsed)
		assert(err == nil)
		str := cast(string)bytes
		fmt.println(str)
	}
}

[cstrachan88]

Null values are being parsed in as json.Null which is a distinct rawptr. I updated the json.marshal_to_writer proc to recognize null pointers. Your example is now working as expected.