Type error on server-side unary-unary handler code

[sublee]

Summary

Incompatible type error on generated unary-unary handler code.

Reproduction Steps

Write reproduce.proto:

syntax = "proto3";
package reproduce;

service X {
  rpc Y(Z) returns (Z) {}
}

message Z {}

Generate code with betterproto==2.0.0b6:

$ protoc -I . --python_betterproto_out=. reproduce.proto

Verify type error by mypy==1.8.0:

$ mypy reproduce/__init__.py

Expected Results

No mypy error

Actual Results

reproduce/__init__.py:55: error: Argument 1 to "y" of "XBase" has incompatible type "Z | None"; expected "Z"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

Here's a chunk of the generated code which has the type error:

class XBase(ServiceBase):
    async def __rpc_y(self, stream: "grpclib.server.Stream[Z, Z]") -> None:
        request = await stream.recv_message()
        response = await self.y(request)
        #                       ^^^^^^^ Argument 1 to "y" of "XBase" has incompatible type "Z | None"; expected "Z"  [arg-type]
        await stream.send_message(response)

stream.recv_message() returns Optional[Z] so request might be None when the connection closes. But self.y() doesn't accept None because it's parameter type is Z but not Optional[Z].

System Information

libprotoc 25.3
Python 3.11.6

Name: betterproto
Version: 2.0.0b6
Summary: A better Protobuf / gRPC generator & library
Home-page: https://github.com/danielgtaylor/python-betterproto
Author: Daniel G. Taylor
Author-email: [email protected]
License: MIT
Location: .../.venv/lib/python3.11/site-packages
Requires: grpclib, python-dateutil
Required-by:

Name: grpclib
Version: 0.4.7
Summary: Pure-Python gRPC implementation for asyncio
Home-page: https://github.com/vmagamedov/grpclib
Author: Vladimir Magamedov
Author-email: [email protected]
License: BSD-3-Clause
Location: .../.venv/lib/python3.11/site-packages
Requires: h2, multidict
Required-by: betterproto

Name: mypy
Version: 1.8.0
Summary: Optional static typing for Python
Home-page: https://www.mypy-lang.org/
Author: Jukka Lehtosalo
Author-email: [email protected]
License: MIT
Location: .../.venv/lib/python3.11/site-packages
Requires: mypy-extensions, typing-extensions
Required-by:

Checklist

• [X] I have searched the issues for duplicates.
• [X] I have shown the entire traceback, if possible.
• [X] I have verified this issue occurs on the latest prelease of betterproto which can be installed using pip install -U --pre betterproto, if possible.