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sglang/test/registered/unit/model_loader/test_transformers_fallback.py
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"""Unit tests for the shared Transformers-fallback loader path in SGLang."""
import unittest
from types import SimpleNamespace
from unittest.mock import patch
from sglang.srt.models.transformers import TransformersBase
from sglang.srt.runtime_context import get_parallel
from sglang.test.ci.ci_register import register_cpu_ci
from sglang.test.test_utils import CustomTestCase
register_cpu_ci(est_time=11, suite="base-a-test-cpu")
class TestTransformersFallbackWeightMapper(CustomTestCase):
def test_gpt_neox_prefix_rewrites(self):
# GPT-NeoX checkpoints (Pythia, gpt-neox-20b) wrap the backbone under
# `gpt_neox.` and expose the LM head as `embed_out.`. `AutoModel`
# returns the backbone as `self.model` and `CausalMixin` installs a
# `ParallelLMHead` at `self.lm_head`, so the fallback mapper must
# rewrite both prefixes. Without these rules, `load_weights` raises
# unexpected-key errors on every `gpt_neox.*` / `embed_out.*` entry.
mapped = TransformersBase.hf_to_sglang_mapper.apply_list(
[
"gpt_neox.embed_in.weight",
"gpt_neox.layers.0.mlp.dense_h_to_4h.weight",
"gpt_neox.final_layer_norm.weight",
"embed_out.weight",
]
)
self.assertEqual(
mapped,
[
"model.embed_in.weight",
"model.layers.0.mlp.dense_h_to_4h.weight",
"model.final_layer_norm.weight",
"lm_head.weight",
],
)
class TestTransformersFallbackSkipSubstrs(CustomTestCase):
def test_init_registers_attention_bias_skip(self):
# Older GPT-NeoX checkpoints (pythia-1.4b, gpt-neox-20b) ship a
# persistent `attention.bias` causal-mask buffer. Newer transformers
# builds register it as `persistent=False`, so it is absent from the
# constructed module tree and `AutoWeightsLoader` raises on the
# unexpected key unless the fallback tells it to skip. The pre-existing
# `.attn.bias` covers GPT-2, not NeoX, so `.attention.bias` must be its
# own entry.
stub = TransformersBase.__new__(TransformersBase)
class _Stop(RuntimeError):
pass
with (
# `__init__` only stashes the pipeline group, so an empty
# stand-in carries it past the read.
get_parallel().override(pp_group=SimpleNamespace()),
patch(
"sglang.srt.models.transformers.get_hf_text_config",
return_value=SimpleNamespace(),
),
patch(
"sglang.srt.models.transformers._resolve_attention_backend_model_cls",
side_effect=_Stop,
),
self.assertRaises(_Stop),
):
TransformersBase.__init__(stub, config=SimpleNamespace())
self.assertIn(".attention.bias", stub.skip_substrs)
if __name__ == "__main__":
unittest.main()