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vllm/tests/v1/spec_decode/test_dflash_causality.py

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Python

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
"""Config-only resolution of DFlash draft attention causality.
``dflash_has_any_non_causal`` decides pre-build whether the draft needs a
non-causal-capable backend, so its branch table (explicit override, SWA-derived
per-layer causality, and the no-``layer_types`` fallback) is worth pinning.
"""
from types import SimpleNamespace
import pytest
from vllm.model_executor.models.qwen3_dflash import (
_dflash_layer_causal,
dflash_has_any_non_causal,
)
def _config(num_hidden_layers, layer_types=None, causal_override=None):
dflash_config = None if causal_override is None else {"causal": causal_override}
return SimpleNamespace(
num_hidden_layers=num_hidden_layers,
layer_types=layer_types,
dflash_config=dflash_config,
)
@pytest.mark.parametrize(
"config,expected",
[
# Override forces causality on every layer, ignoring layer_types.
(_config(2, layer_types=["full_attention"] * 2, causal_override=True), False),
# Override forces non-causal on every layer.
(
_config(2, layer_types=["sliding_attention"] * 2, causal_override=False),
True,
),
# SWA-derived: full-attention layers are non-causal.
(_config(2, layer_types=["sliding_attention", "full_attention"]), True),
# SWA-derived: all-sliding is fully causal.
(_config(2, layer_types=["sliding_attention", "sliding_attention"]), False),
# No layer_types -> non-causal fallback.
(_config(2, layer_types=None), True),
(_config(2, layer_types=[]), True),
],
)
def test_dflash_has_any_non_causal(config, expected):
assert dflash_has_any_non_causal(config) is expected
def test_dflash_layer_causal_is_per_layer():
config = _config(2, layer_types=["sliding_attention", "full_attention"])
assert _dflash_layer_causal(config, 0) is True
assert _dflash_layer_causal(config, 1) is False