proto3 optional feature

[Opa-]

Hello,

I'm currently converting some services to Temporal workers. These services already defines Protobuf files and sometimes rely on optional fields.

I'm getting warning message when using those proto messages. Here is a simple example :

syntax = "proto3";

package foo.v1;

import "temporal/v1/temporal.proto";

service FooService {
    option (temporal.v1.service) = {
        task_queue: "foo-queue"
    };

    rpc Foo (FooInput) returns (FooOutput) {
        option (temporal.v1.workflow) = {};
        option (temporal.v1.activity) = {
            start_to_close_timeout: {seconds: 2}
        };
    }
}

message FooInput {
    optional string bar = 1;
}

message FooOutput {
    optional string bar = 1;
}

WARN	plugin "protoc-gen-go_temporal" does not support required features.
  Feature "proto3 optional" is required by 1 file(s):
    foo/v1/foo.proto

The generated code do not work either as the generated UnmarshalCliFlagsToFooInput will consider the field to be oneof (here https://github.com/cludden/protoc-gen-go-temporal/blob/main/internal/plugin/cli.go#L944) and use unresolved references XBar and unresolved type FooInput_Bar :

if cmd.IsSet("bar") {
    hasValues = true
    result.XBar = &FooInput_Bar{Bar: cmd.String("bar")}
}

Resulting in the following error :

gen/foo/v1/foo_temporal.pb.go:1181:10: result.XBar undefined (type FooInput has no field or method XBar)
gen/foo/v1/foo_temporal.pb.go:1181:18: undefined: FooInput_Bar

If using proto2 there's not warning, the field is not considered as oneof (here https://github.com/cludden/protoc-gen-go-temporal/blob/main/internal/plugin/cli.go#L947) but the generated code do not work either as cmd.String is returning a string where the field is actually a *string.

if cmd.IsSet("bar") {
    hasValues = true
    result.Bar = cmd.String("bar")
}

gen/foo/v1/foo_temporal.pb.go:1181:16: cannot use cmd.String("bar") (value of type string) as *string value in assignment

Is there any technical reason/limitation or design philosophy not to support optional feature ? And if not would you think it would be possible to add support for it ?

Note that the issue seems to be only related to the generated CLI as buf with option cli-enabled=false do not generate any invalid code.

Thanks