Invalid cast error when printing extern unions

[nikneym]

Zig Version

0.14.0-dev.3357+c44f4501e

Steps to Reproduce and Observed Behavior

It seems printing a union with at least 2 void fields results in unexpected errors. To reproduce:

const std = @import("std");

const Union = extern struct {
    data: extern union {
        first: void,
        second: void,
    },
};

pub fn main() !void {
    const a = Union{
        .data = .{
            .first = {},
        },
    };

    std.debug.print("{}\n", .{a});
}

This creates regular unexpected error output. However, you can get a fancy LLVM one too if you also provide an enum with explicit tag type:

const std = @import("std");

const EnumAndUnion = extern struct {
    enumeration: enum(u8) { first, second },
    data: extern union {
        first: void,
        second: void,
    },
};

pub fn main() !void {
    const a = EnumAndUnion{
        .enumeration = .first,
        .data = .{
            .first = {},
        },
    };

    std.debug.print("{}\n", .{a});
}

run
└─ run repro
   └─ install
      └─ install repro
         └─ zig build-exe repro Debug native failure
error: error: Invalid cast (Producer: 'zig 0.14.0' Reader: 'LLVM 19.1.7')

Expected Behavior

It should print out correctly.