[core:encoding/json] Incorrect bit_set Value When Unmarshalling

[dozn]

Context

package main
import "core:encoding/json"
import "core:fmt"
main :: proc() {
  Entity :: bit_set[EntityFlag; u64]
  EntityFlag :: enum { Player }
  save_data := Entity{.Player}
  fmt.println("original: ", save_data)

  bytes, err_marshal := json.marshal(save_data)
  if err_marshal != nil { fmt.panicf("%s", err_marshal) }
  fmt.println("marshal:  ", string(bytes))

  save_data = {}
  if err_unmarshal := json.unmarshal(bytes, &save_data); err_unmarshal != nil {
    fmt.panicf("%s", err_unmarshal)
  }
  fmt.println("unmarshal:", save_data)
}

Expected Behavior

original:  bit_set[EntityFlag; u64]{Player}
marshal:   1
unmarshal: bit_set[EntityFlag; u64]{Player}

Current Behavior

original:  bit_set[EntityFlag; u64]{Player}
marshal:   1
unmarshal: bit_set[EntityFlag; u64]{56}

Notes

• cbor works
• works when i/u8, broken with 16/32/64
• it's hitting the byte_swaps at

  Odin/core/encoding/json/unmarshal.odin

  Lines 130 to 136 in 6572a52

  	x^ = do_byte_swap ? intrinsics.byte_swap(u16(i)) : u16(i)
  	case 32:
  	x := (^u32)(v.data)
  	x^ = do_byte_swap ? intrinsics.byte_swap(u32(i)) : u32(i)
  	case 64:
  	x := (^u64)(v.data)
  	x^ = do_byte_swap ? intrinsics.byte_swap(u64(i)) : u64(i)

  which messes up the values (see comment by Barinzaya), because it's hitting

  Odin/core/reflect/reflect.odin

  Line 1021 in 6572a52

  case .Platform: return ODIN_ENDIAN == .Big

  and thinks it's big endian

---

Odin: dev-2025-01:bca016ae9
OS: Windows 11 Professional (version: 23H2), build 22631.4751
CPU: AMD Ryzen 7 3700X 8-Core Processor
RAM: 65457 MiB
Backend: LLVM 18.1.8

[Barinzaya]

It doesn't look like the problem is that it thinks the bit_set is big endian, it looks like the logic for when to swap bytes is wrong.

do_byte_swap := !reflect.bit_set_is_big_endian(v)

This swaps the bytes whenever the bit_set isn't big endian--meaning it always makes the bit_set big endian swaps the bytes when the bit set is little endian, regardless of the platform. Seems like it should be:

do_byte_swap := reflect.bit_set_is_big_endian(v) != (ODIN_ENDIAN == .Big)

or equivalent. Basically, swap the bytes when the bit_set's endianness is different from the platform's.