If you attempt to dir.walk on a fs.openDir without setting .{ .iterable = true } in fs.openDir you will get the error:
thread 42910 panic: reached unreachable code
/home/user/.zig/lib/std/posix.zig:5170:18: 0x14f21c9 in lseek_SET (build)
.BADF => unreachable, // always a race condition