fix(serve-grpc): clearer error when given a new-SDK service

src/bentoml/serving.py

@@ -590,6 +590,18 @@ def serve_grpc_production(
     svc = load(bento_identifier, working_dir=working_dir)
 
     if not isinstance(svc, Service):
+        try:
+            from _bentoml_sdk import Service as NewService
+        except ImportError:
+            NewService = None  # type: ignore[assignment]
+        if NewService is not None and isinstance(svc, NewService):
+            raise BentoMLException(
+                "gRPC serving is not supported for services defined with the "
+                "`@bentoml.service` decorator (the bentoml>=1.2 programming "
+                "model). Use `bentoml serve` to run the service over HTTP, or "
+                "rewrite it using the legacy `bentoml.Service` API if gRPC is "
+                "required."
+            )
         raise BentoMLException(f"{type(svc)} type doesn't support gRPC serving")
 
     from circus.sockets import CircusSocket  # type: ignore

tests/unit/test_serve_grpc_new_sdk_error.py

@@ -0,0 +1,50 @@
+"""Regression test for bentoml#5607.
+
+`serve-grpc` used to fail with the unhelpful message::
+
+    <class '_bentoml_sdk.service.factory.Service'> type doesn't support gRPC serving
+
+when pointed at a service defined with the `@bentoml.service` decorator
+(the bentoml>=1.2 programming model). gRPC is only implemented for the
+legacy `bentoml.Service` API, so this case should raise a clear error
+that tells the user what to do instead.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from bentoml.exceptions import BentoMLException
+from bentoml.serving import serve_grpc_production
+
+NEW_SDK_SERVICE = """
+from __future__ import annotations
+
+import bentoml
+
+
+@bentoml.service(name="grpc_smoke")
+class Supervisor:
+    @bentoml.api
+    def greet(self, name: str = "world") -> str:
+        return f"hello {name}"
+"""
+
+
+def test_serve_grpc_rejects_new_sdk_service_with_clear_message(
+    tmp_path: Path,
+) -> None:
+    (tmp_path / "service.py").write_text(NEW_SDK_SERVICE)
+
+    with pytest.raises(BentoMLException) as exc_info:
+        serve_grpc_production(
+            "service.py:Supervisor",
+            working_dir=str(tmp_path),
+        )
+
+    message = str(exc_info.value)
+    assert "gRPC serving is not supported" in message
+    assert "@bentoml.service" in message
+    assert "bentoml serve" in message