Export generated code in module

[qxxxb]

I was wondering if there a way to export code generated from a parseProto call. Currently I can do something like this:

syntax = "proto3";
// client_msg.proto

message ClientMsg {
    enum Kind {
        RequestInfo = 0;
        Connect = 1;
        Disconnect = 2;
        GameInput = 3;
    }

    enum GameInput {
        MoveLeft = 0;
        MoveRight = 1;
        MoveUp = 2;
        MoveDown = 3;
    }

    Kind kind = 1;
    repeated GameInput gameInputs = 2;
}

# client_msg.nim
import protobuf

parseProtoFile("client_msg.proto")

export initClientMsg
export ClientMsgKind
export ClientMsg
export write
export readClientMsg
export has
type GameInput* = ClientMsg_GameInput

In another module, when I use the client_msg module, some things work, and others don't.

# client.nim
import streams, ./client_msg

var msg = initClientMsg(
  kind = ClientMsgKind.GameInput,
  gameInputs = @[GameInput.MoveLeft, GameInput.MoveUp]
)

var stream = newStringStream()
stream.write(msg) # Compile error: type mismatch: got <ClientMsg>

var readMsg = stream.readClientMsg()
if readMsg.has(kind):
  echo readMsg.kind # Compile error: expression '.' cannot be called

[PMunch]

This has to do with how this protobuf implementation masks the fields. If you look at -d:echoProtobuf you can see the code that's actually generated. This code calls the makeDot helper that creates . and .= operators that will verify that the field is actually initialised in the object. I don't quite remember why I didn't use the Option type for this, but it might've been because options can be clunky to work with (at least without using my optionsutils package :)), but it might've been a better reason for it as well.

So the problem here is that you aren't exporting everything that protobuf needs to properly access that objects fields. If you include

export `.`
export `getField`

in your client_msg.nim file it should work fine. You might also want to add a stream.setPosition(0) after your stream.write call however if you actually want to read the object back in ;)

It might be worth adding a exportType macro or template to protobuf that creates a block like this automatically so this process is easier. Or at least a exportProtobuf template that exports the common procedures like ., .=, write, has, etc.

[PMunch]

Created the exportMessage macro to make things easier, https://github.com/PMunch/protobuf-nim#exporting-message-definitions. So your client_msg.nim file can now be simplified as:

# client_msg.nim
import protobuf

parseProtoFile("client_msg.proto")

exportMessage ClientMsg

export ClientMsgKind
type GameInput* = ClientMsg_GameInput

[qxxxb]

Wow thanks! I'll try this out