[Model] Prioritize Transformers fallback over suffix matching (#21719)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/models/multimodal/generation/test_common.py

@@ -222,6 +222,7 @@ VLM_TEST_SETTINGS = {
         },
         marks=[large_gpu_mark(min_gb=32)],
     ),
+    # Check "auto" with fallback to transformers
     "internvl-transformers": VLMTestInfo(
         models=["OpenGVLab/InternVL3-1B-hf"],
         test_type=(VLMTestType.IMAGE, VLMTestType.MULTI_IMAGE),
@@ -231,7 +232,7 @@ VLM_TEST_SETTINGS = {
         use_tokenizer_eos=True,
         image_size_factors=[(0.25, 0.5, 1.0)],
         vllm_runner_kwargs={
-            "model_impl": "transformers",
+            "model_impl": "auto",
         },
         auto_cls=AutoModelForImageTextToText,
         marks=[pytest.mark.core_model],

vllm/model_executor/models/registry.py

@@ -586,18 +586,6 @@ class _ModelRegistry:
 
         return architecture
 
-    def _normalize_archs(
-        self,
-        architectures: list[str],
-        model_config: ModelConfig,
-    ) -> list[str]:
-        if not architectures:
-            logger.warning("No model architectures are specified")
-
-        return [
-            self._normalize_arch(arch, model_config) for arch in architectures
-        ]
-
     def inspect_model_cls(
         self,
         architectures: Union[str, list[str]],
@@ -605,8 +593,8 @@ class _ModelRegistry:
     ) -> tuple[_ModelInfo, str]:
         if isinstance(architectures, str):
             architectures = [architectures]
-
-        normalized_archs = self._normalize_archs(architectures, model_config)
+        if not architectures:
+            raise ValueError("No model architectures are specified")
 
         # Require transformers impl
         if model_config.model_impl == ModelImpl.TRANSFORMERS:
@@ -617,13 +605,26 @@ class _ModelRegistry:
                 if model_info is not None:
                     return (model_info, arch)
 
-        for arch, normalized_arch in zip(architectures, normalized_archs):
+        # Fallback to transformers impl (after resolving convert_type)
+        if (all(arch not in self.models for arch in architectures)
+                and model_config.model_impl == ModelImpl.AUTO
+                and getattr(model_config, "convert_type", "none") == "none"):
+            arch = self._try_resolve_transformers(architectures[0],
+                                                  model_config)
+            if arch is not None:
+                model_info = self._try_inspect_model_cls(arch)
+                if model_info is not None:
+                    return (model_info, arch)
+
+        for arch in architectures:
+            normalized_arch = self._normalize_arch(arch, model_config)
             model_info = self._try_inspect_model_cls(normalized_arch)
             if model_info is not None:
                 return (model_info, arch)
 
-        # Fallback to transformers impl
-        if model_config.model_impl in (ModelImpl.AUTO, ModelImpl.TRANSFORMERS):
+        # Fallback to transformers impl (before resolving runner_type)
+        if (all(arch not in self.models for arch in architectures)
+                and model_config.model_impl == ModelImpl.AUTO):
             arch = self._try_resolve_transformers(architectures[0],
                                                   model_config)
             if arch is not None:
@@ -640,8 +641,8 @@ class _ModelRegistry:
     ) -> tuple[type[nn.Module], str]:
         if isinstance(architectures, str):
             architectures = [architectures]
-
-        normalized_archs = self._normalize_archs(architectures, model_config)
+        if not architectures:
+            raise ValueError("No model architectures are specified")
 
         # Require transformers impl
         if model_config.model_impl == ModelImpl.TRANSFORMERS:
@@ -652,13 +653,26 @@ class _ModelRegistry:
                 if model_cls is not None:
                     return (model_cls, arch)
 
-        for arch, normalized_arch in zip(architectures, normalized_archs):
+        # Fallback to transformers impl (after resolving convert_type)
+        if (all(arch not in self.models for arch in architectures)
+                and model_config.model_impl == ModelImpl.AUTO
+                and getattr(model_config, "convert_type", "none") == "none"):
+            arch = self._try_resolve_transformers(architectures[0],
+                                                  model_config)
+            if arch is not None:
+                model_cls = self._try_load_model_cls(arch)
+                if model_cls is not None:
+                    return (model_cls, arch)
+
+        for arch in architectures:
+            normalized_arch = self._normalize_arch(arch, model_config)
             model_cls = self._try_load_model_cls(normalized_arch)
             if model_cls is not None:
                 return (model_cls, arch)
 
-        # Fallback to transformers impl
-        if model_config.model_impl in (ModelImpl.AUTO, ModelImpl.TRANSFORMERS):
+        # Fallback to transformers impl (before resolving runner_type)
+        if (all(arch not in self.models for arch in architectures)
+                and model_config.model_impl == ModelImpl.AUTO):
             arch = self._try_resolve_transformers(architectures[0],
                                                   model_config)
             if arch is not None: