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from dataclasses import dataclass

import pytest
import torch

import cutlass
import cutlass.cute as cute
from cutlass.cute.runtime import from_dlpack


@dataclass
class A:
    pass


@dataclass
class B:
    pass


@cute.kernel
def _test_empty_dataclass_kernel(out: cute.Tensor, tag: A | B):
    tidx, _, _ = cute.arch.thread_idx()
    if tidx == 0:
        match tag:
            case A():
                out[0] = 0
            case B():
                out[0] = 1


@cute.jit
def _test_empty_dataclass_host(out: cute.Tensor, tag: A | B):
    _test_empty_dataclass_kernel(out, tag).launch(grid=[1, 1, 1], block=[1, 1, 1])


@pytest.mark.parametrize("tag,expected", [(A(), 0), (B(), 1)])
def test_empty_dataclass_union(tag, expected):
    out = torch.zeros(1, device="cuda", dtype=torch.int32)
    out_cute = from_dlpack(out).mark_layout_dynamic()
    compiled_fn = cute.compile(_test_empty_dataclass_host, out_cute, tag)
    compiled_fn(out_cute, tag)
    torch.cuda.synchronize()
    assert out.item() == expected