Unexpected behavior for #shared_nil on union of pointer types

[nb-ohad]

Context

A union of pointers of types, tagged with #shared_nil, treats a pointer to an empty struct type (pointer to struct {}) as a normalized nil value for the union.

This behavior is unexpected, and in my opinion contradicts the definition of the #shared_nil tag. My reasoning is that given type definition T :: struct {} the value ^T{} is not a pointer nil value nor a zero value for ^T

Operating System: macOS 14.5 (23F79)
Odin: dev-2025-01-nightly:2aae4cf
OS: macOS Unknown
CPU: Apple M1 Pro
RAM: 32768 MiB
Backend: LLVM 18.1.8

Expected Behavior

The following program should be able to run to a successful termination

package main

Type_A :: struct { value : int }
Type_B :: struct { }

Union_Of_Pointers :: union #shared_nil {
    ^Type_A,
    ^Type_B,
}

main :: proc() {
    p : Union_Of_Pointers
    assert(p == nil)

    p = new(Type_A) 
    assert(p != nil)

    p = new(Type_B)
    assert(p != nil)
}

Current Behavior

The first and second assertions checks passes but the third assertion fails where it should not

Steps to Reproduce

1. Copy the code snippet form the expected behavior section into a new odin file
2. run odin run .

[nb-ohad]

Might be related to: #1202