Union fields overwritten in an unexpected way

[HulluKana]

Zig Version

0.13.0

Steps to Reproduce and Observed Behavior

main.zig:

const std = @import("std");

const Struct = struct { a: u32, b: u32 };
const Union = union { x: u32, y: Struct };

pub fn main() !void {
    var example = Union{ .x = 1 };
    example = .{ .y = .{ .a = 2, .b = example.x } };
    std.debug.print("{d}\n", .{example.y.b});
}

run zig build run and get 2 as output

Below is a link to the compiler explorer page containing the same code in both zig and c++ alongside the outputted assembly and printed result.
https://godbolt.org/z/bTYGqWqE9
You can see that c++ outputs 1 whereas zig outputs 2. Taking a look at the assembly, gcc achieves this result by saving the previous value of the example union to eax before overwriting the memory in that address. Zig, however, overwrites the address of the previous value before saving it anywhere, giving the unexpected result of 2.

Expected Behavior

The expected behavior is exactly what gcc does in the linked compiler explorer page. However, if zig overwriting the previous result without saving it is intentional, I would have expected there to be a compiler error. Instead, zig failed silently.

[cryptocode]

See #12251 and linked issues

[HulluKana]

I see. I didn't notice that when looking for duplicates. Well, I guess I can close this issue then.