// Union struct-literal initialization — a union may be built with a struct
// literal that sets a SINGLE arm: one direct member, or several promoted
// members of the same anonymous-struct arm. Equivalent to the `--- `+per-field
// form, and the two views stay consistent (type-punning still works).
//
// Regression (issue 0158): a union literal previously fell through the generic
// struct-literal path (getStructFields returns empty for a union), building a
// malformed structInit whose overlapping zero-fill clobbered the named member —
// `b : Overlay = .{ f = 3.14 }` silently read back 0.0. Now it lowers like the
// `--- `+member-write form: each named member is written into a union-sized slot.
#import "modules/std.sx";

Overlay :: union { f: f32; i: i32; }
Vec2 :: union { data: [2]f32; struct { x, y: f32; }; }

main :: () {
    // Single-member literal — the bug case. Reads back the value, and a
    // type-punning read of the other member sees the same bytes.
    b : Overlay = .{ f = 3.14 };
    print("b.f={} b.i={}\n", b.f, b.i);

    // Equivalence: the `--- `+member-write form produces identical bytes.
    a : Overlay = ---;
    a.f = 3.14;
    print("a.f={} a.i={}\n", a.f, a.i);

    // Promoted members of the anonymous-struct arm: both belong to the same
    // arm (offsets 0 and 4), so naming both is valid; the `data` view overlays.
    v : Vec2 = .{ x = 1.0, y = 2.0 };
    print("v.x={} v.y={} d0={} d1={}\n", v.x, v.y, v.data[0], v.data[1]);

    // Empty literal → undefined union (same as `---`); set a member after.
    e : Overlay = .{};
    e.i = 9;
    print("e.i={}\n", e.i);
}