[api] Make generated encode and size entry points type erased (#19015)

tests/integration/fixtures/api_empty_message_roundtrip.yaml

@@ -0,0 +1,11 @@
+esphome:
+  name: api-empty-message-test
+host:
+api:
+logger:
+  level: DEBUG
+
+switch:
+  - platform: template
+    name: "Empty Message Switch"
+    optimistic: true

tests/integration/test_api_empty_message_roundtrip.py

@@ -0,0 +1,37 @@
+"""Messages without fields go through the shared ProtoMessage entry points on both directions."""
+
+from __future__ import annotations
+
+from aioesphomeapi import api_pb2
+import pytest
+
+from .raw_api_client import MESSAGE_TYPE_OF, RawApiClient
+from .types import RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_api_empty_message_roundtrip(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    unused_tcp_port: int,
+) -> None:
+    async with run_compiled(yaml_config), RawApiClient(unused_tcp_port) as client:
+        await client.connect()
+
+        # Field free request and reply on the plain send path
+        await client.send_message(api_pb2.PingRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.PingResponse])
+
+        # Field free request answered by a message with fields, and a list that ends with
+        # the field free ListEntitiesDoneResponse through the batching path
+        await client.send_message(api_pb2.DeviceInfoRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.DeviceInfoResponse])
+        await client.send_message(api_pb2.ListEntitiesRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.ListEntitiesDoneResponse])
+        assert (
+            client.frame_counts[MESSAGE_TYPE_OF[api_pb2.ListEntitiesSwitchResponse]]
+            == 1
+        )
+
+        await client.send_message(api_pb2.DisconnectRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.DisconnectResponse])

tests/unit_tests/components/api/test_api_proto.py

@@ -194,17 +194,17 @@ def test_superseded_device_info_fields_still_declared_in_header() -> None:
 
 def test_superseded_device_info_fields_still_encoded_and_sized() -> None:
     """Each superseded field must still be touched by DeviceInfoResponse's
-    generated encode() and calculate_size(), i.e. it is still put on the wire.
+    generated encode_msg() and calc_size_msg(), i.e. it is still put on the wire.
     """
-    encode_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::encode")
-    size_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::calculate_size")
+    encode_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::encode_msg")
+    size_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::calc_size_msg")
     for field_name in SUPERSEDED_FIELDS:
-        assert f"this->{field_name}" in encode_body, (
-            f"DeviceInfoResponse::encode() no longer references {field_name}. "
+        assert f"msg.{field_name}" in encode_body, (
+            f"DeviceInfoResponse::encode_msg() no longer references {field_name}. "
             f"{DEPRECATED_FIELD_TRAP}"
         )
-        assert f"this->{field_name}" in size_body, (
-            f"DeviceInfoResponse::calculate_size() no longer references "
+        assert f"msg.{field_name}" in size_body, (
+            f"DeviceInfoResponse::calc_size_msg() no longer references "
             f"{field_name}. {DEPRECATED_FIELD_TRAP}"
         )