[Misc] Improve error message for `is_multimodal` (#30483)

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

vllm/model_executor/models/interfaces.py

@@ -53,6 +53,22 @@ The output embeddings must be one of the following formats:
 """
 
 
+def _require_is_multimodal(is_multimodal: Tensor | None) -> Tensor:
+    """
+    A helper function to be used in the context of
+    [vllm.model_executor.models.interfaces.SupportsMultiModal.embed_input_ids][]
+    to provide a better error message.
+    """
+    if is_multimodal is None:
+        raise ValueError(
+            "`embed_input_ids` now requires `is_multimodal` arg, "
+            "please update your model runner according to "
+            "https://github.com/vllm-project/vllm/pull/16229."
+        )
+
+    return is_multimodal
+
+
 @runtime_checkable
 class SupportsMultiModal(Protocol):
     """The interface required for all multi-modal models."""
@@ -190,12 +206,10 @@ class SupportsMultiModal(Protocol):
         if multimodal_embeddings is None or len(multimodal_embeddings) == 0:
             return inputs_embeds
 
-        assert is_multimodal is not None
-
         return _merge_multimodal_embeddings(
             inputs_embeds=inputs_embeds,
             multimodal_embeddings=multimodal_embeddings,
-            is_multimodal=is_multimodal,
+            is_multimodal=_require_is_multimodal(is_multimodal),
         )
 
 

vllm/model_executor/models/phi3v.py

@@ -64,6 +64,7 @@ from .interfaces import (
     SupportsMultiModal,
     SupportsPP,
     SupportsQuant,
+    _require_is_multimodal,
 )
 from .utils import (
     AutoWeightsLoader,
@@ -687,12 +688,10 @@ class Phi3VForCausalLM(nn.Module, SupportsMultiModal, SupportsPP, SupportsQuant)
         if multimodal_embeddings is None or len(multimodal_embeddings) == 0:
             return inputs_embeds
 
-        assert is_multimodal is not None
-
         return _merge_multimodal_embeddings(
             inputs_embeds=inputs_embeds,
             multimodal_embeddings=multimodal_embeddings,
-            is_multimodal=is_multimodal,
+            is_multimodal=_require_is_multimodal(is_multimodal),
         )
 
     def forward(

vllm/model_executor/models/qwen3_vl.py

@@ -93,6 +93,7 @@ from .interfaces import (
     SupportsMRoPE,
     SupportsMultiModal,
     SupportsPP,
+    _require_is_multimodal,
 )
 from .qwen2_5_vl import (
     Qwen2_5_VisionAttention,
@@ -1572,7 +1573,7 @@ class Qwen3VLForConditionalGeneration(
         if multimodal_embeddings is None or len(multimodal_embeddings) == 0:
             return inputs_embeds
 
-        assert is_multimodal is not None
+        is_multimodal = _require_is_multimodal(is_multimodal)
 
         if self.use_deepstack:
             (