1const U = union {
 2    a: void,
 3    b: u64,
 4};
 5comptime {
 6    var u: U = .{ .a = {} };
 7    const v = u.b;
 8    _ = &u;
 9    _ = v;
10}
11
12// error
13//
14// :7:16: error: access of union field 'b' while field 'a' is active
15// :1:11: note: union declared here