Missing import in generated code when using well known types

Summary

When compiling a proto file which references well known types, protoc should generate the line import betterproto.lib.google.protobuf as betterproto_lib_google_protobuf. This does not happen in the following edge case.

Reproduction Steps

Create a file foo.proto whith the following content

syntax = "proto3";
import "google/protobuf/empty.proto";

service foo {
    rpc foo (google.protobuf.Empty) returns (MyEmpty);
}

message MyEmpty {}

and compile it by running python -m grpc_tools.protoc -I . --python_betterproto_out=lib foo.proto.

Expected Results

The generated file __init__.py references a module betterproto_lib_google_protobuf, so it should import betterproto.lib.google.protobuf as betterproto_lib_google_protobuf.

Note that it actually would be imported if I had used google.protobuf.Empty as the return value of the RPC above.

Actual Results

The generated file __init__.py does not import betterproto.lib.google.protobuf as betterproto_lib_google_protobuf

System Information

libprotoc 25.0
Python 3.10.12
betterproto 2.0.0b6 (tested with released version and github master branch)

Checklist

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

首先使用 foo.proto 和所述的 python -m grpc_tools.protoc 命令复现问题，然后检查生成的 init.py。比较将 google.protobuf.Empty 用作 RPC 返回值时的输出。当边界情况的输出在所引用的别名下导入 betterproto.lib.google.protobuf，且生成的代码能够成功编译时，即表示完成。