Cannot compile protobuf definition with edition syntax

Question

I am trying to compile the following .proto file:

edition = "2023";
package example_proto;
import "google/protobuf/cpp_features.proto";
message BidAsk {
 required double bid = 1;
 required double ask = 2;
 required string timestamp = 3 [features.(pb.cpp).string_type = VIEW];
}

As far as I am aware, this matches the requirements specified in this documentation page.

• https://protobuf.dev/editions/overview/

I am aware that required is not usually recommended, however in this case it does not make sense to have a BidAsk message without all of the fields populated, and this message will never change or be extended.

When I run protoc on this file, I get the following error.

$ protoc bid_ask.proto --cpp_out=test
[libprotobuf WARNING google/protobuf/compiler/parser.cc:646] No syntax specified for the proto file: bid_ask.proto. Please use 'syntax = "proto2";' or 'syntax = "proto3";' to specify a syntax version. (Defaulted to proto2 syntax.)
bid_ask.proto:1:1: Expected top-level statement (e.g. "message").

Update: I think this is caused by an out-of-date protobuf compiler.

$ protoc --version
libprotoc 3.21.12

I think this is too old to support the edition syntax.

This is a bit surprising since I installed protoc via apt install protobuf-compiler. The host OS is Ubuntu 24.10, which is quite recent. I'm not sure why the version of protoc supplied via the package manager is so old.

I will ask a seperate question about how to update it.

• user2138149: @drescherjm That appears to be an error itself. edition is not compatiable with syntax, according to the documentation. I have tried it, but adding either option made no difference.

Answer 1

I have now confirmed that the issue was caused by an out-of-date protoc and protobuf development libraries.

Ubuntu 24.10 ships with a version of the protobuf development libs which does not support this more recent protobuf syntax.

To solve the issue, I used a combination of vcpkg with my C++ project to obtain access to a more recent version of the protobuf dev libs.