[Bug] Fix TypeError when hf_config.architectures is None during model loading (#38849)

Signed-off-by: Tihomir Elek <tiho.elek@gmail.com>

tests/test_config.py

@@ -4,12 +4,14 @@
 import logging
 import os
 from dataclasses import MISSING, Field, asdict, dataclass, field
+from types import SimpleNamespace
 from unittest.mock import patch
 
 import pydantic
 import pytest
 from pydantic import ValidationError
 
+import vllm.config.vllm as vllm_config_module
 from vllm.compilation.backends import VllmBackend
 from vllm.config import (
     CompilationConfig,
@@ -45,6 +47,81 @@ def test_compile_config_repr_succeeds():
     assert "inductor_passes" in val
 
 
+@pytest.mark.skip_global_cleanup
+def test_with_hf_config_populates_missing_architectures_from_causal_lm_mapping(
+    monkeypatch,
+):
+    monkeypatch.setattr(
+        vllm_config_module,
+        "replace",
+        lambda self, **kwargs: SimpleNamespace(**kwargs),
+    )
+    cfg = SimpleNamespace(
+        model_config=SimpleNamespace(
+            is_multimodal_model=False,
+            hf_config=SimpleNamespace(),
+            get_model_arch_config=lambda: "arch-config",
+        )
+    )
+    hf_config = SimpleNamespace(model_type="mistral", architectures=None)
+
+    updated = VllmConfig.with_hf_config(cfg, hf_config)
+
+    assert updated.model_config.hf_config.architectures == ["MistralForCausalLM"]
+    assert hf_config.architectures is None
+
+
+@pytest.mark.skip_global_cleanup
+def test_with_hf_config_preserves_explicit_architectures_override(monkeypatch):
+    monkeypatch.setattr(
+        vllm_config_module,
+        "replace",
+        lambda self, **kwargs: SimpleNamespace(**kwargs),
+    )
+    cfg = SimpleNamespace(
+        model_config=SimpleNamespace(
+            is_multimodal_model=False,
+            hf_config=SimpleNamespace(),
+            get_model_arch_config=lambda: "arch-config",
+        )
+    )
+    hf_config = SimpleNamespace(model_type="mistral", architectures=None)
+
+    updated = VllmConfig.with_hf_config(
+        cfg,
+        hf_config,
+        architectures=["Ministral3ForCausalLM"],
+    )
+
+    assert updated.model_config.hf_config.architectures == ["Ministral3ForCausalLM"]
+
+
+@pytest.mark.skip_global_cleanup
+def test_with_hf_config_leaves_unknown_model_type_without_architectures(
+    monkeypatch,
+):
+    monkeypatch.setattr(
+        vllm_config_module,
+        "replace",
+        lambda self, **kwargs: SimpleNamespace(**kwargs),
+    )
+    cfg = SimpleNamespace(
+        model_config=SimpleNamespace(
+            is_multimodal_model=False,
+            hf_config=SimpleNamespace(),
+            get_model_arch_config=lambda: "arch-config",
+        )
+    )
+    hf_config = SimpleNamespace(
+        model_type="not_a_real_model",
+        architectures=None,
+    )
+
+    updated = VllmConfig.with_hf_config(cfg, hf_config)
+
+    assert updated.model_config.hf_config.architectures is None
+
+
 def test_async_scheduling_with_pipeline_parallelism_is_allowed():
     cfg = VllmConfig(
         scheduler_config=SchedulerConfig(

vllm/config/vllm.py

@@ -559,6 +559,16 @@ class VllmConfig:
         if architectures is not None:
             hf_config = copy.deepcopy(hf_config)
             hf_config.architectures = architectures
+        elif hf_config.architectures is None:
+            from transformers.models.auto.modeling_auto import (
+                MODEL_FOR_CAUSAL_LM_MAPPING_NAMES,
+            )
+
+            if hf_config.model_type in MODEL_FOR_CAUSAL_LM_MAPPING_NAMES:
+                hf_config = copy.deepcopy(hf_config)
+                hf_config.architectures = [
+                    MODEL_FOR_CAUSAL_LM_MAPPING_NAMES[hf_config.model_type]
+                ]
 
         model_config = copy.deepcopy(self.model_config)
 

vllm/model_executor/model_loader/utils.py

@@ -175,7 +175,7 @@ _MODEL_ARCH_BY_HASH = dict[int, tuple[type[nn.Module], str]]()
 def _get_model_architecture(model_config: ModelConfig) -> tuple[type[nn.Module], str]:
     from vllm.model_executor.models.adapters import as_embedding_model, as_seq_cls_model
 
-    architectures = getattr(model_config.hf_config, "architectures", [])
+    architectures = getattr(model_config.hf_config, "architectures", None) or []
 
     model_cls, arch = model_config.registry.resolve_model_cls(
         architectures,
@@ -215,7 +215,7 @@ def get_model_architecture(model_config: ModelConfig) -> tuple[type[nn.Module],
             model_config.runner_type,
             model_config.trust_remote_code,
             model_config.model_impl,
-            tuple(getattr(model_config.hf_config, "architectures", [])),
+            tuple(getattr(model_config.hf_config, "architectures", None) or []),
         )
     )
     if key in _MODEL_ARCH_BY_HASH: