Optional fields not supported in proto3 syntax

[jesseduffield]

If I try to generate code with protoc-gen-rust i.e. with the command: protoc --rust_out=out test.proto I get the following error:

test.proto: is a proto3 file that contains optional fields, but code generator protoc-gen-rust hasn't been updated to support optional fields in proto3. Please ask the owner of this code generator to support proto3 optional.--rust_out:

Here's my test.proto file:

syntax = "proto3";

message Test {
  optional string value = 1;
}

Without the optional keyword the command does not raise an error. Likewise, if I change the syntax to proto2, the command does not raise an error.

I installed protoc-gen-rust via cargo install protobuf-codegen (version v3.0.2 was installed).

OS version:

uname -a
Linux 78ae9044ec23 5.10.104-linuxkit #1 SMP Wed Mar 9 19:05:23 UTC 2022 x86_64 Linux

Looking through the docs, it seems that optional fields should be supported, so I'm not sure if I'm doing something wrong or not. My goal is to end up with an Option in the generated rust code.

Thanks :)

[stepancheg]

Interesting. Optional fields work, but when using protobuf-codegen crate, and I didn't test with protoc binary.

If you need to run protoc manually, this need to be implemented (in rust-protobuf): https://github.com/protocolbuffers/protobuf/blob/main/docs/implementing_proto3_presence.md#signaling-that-your-code-generator-supports-proto3-optional

[jesseduffield]

Thanks for the quick response. When you say it needs to be implemented: are you referring to actually implementing support for proto3 optional fields, or do you just mean telling protoc that we already do have support?

[stepancheg]

are you referring to actually implementing support for proto3 optional fields, or do you just mean telling protoc that we already do have support?

The latter, only need to signal to protoc.

proto3 optional is implemented, test.

[jesseduffield]

I believe #626 will do the trick

[stepancheg]

Reopening until it is released.

[stepancheg]

3.0.3