Support additional protoc parameters

[stephanpelikan]

I want to use the "optional" attribute which is an experimental feature (https://github.com/protocolbuffers/protobuf/blob/master/docs/field_presence.md) and has to be enabled using the protoc parameter "--experimental_allow_proto3_optional".

As far as I could figure out, there is no way to add additional protoc parameters using this Maven plugin. Something like

<configuration>
  <additionalParameters>--experimental_allow_proto3_optional</additionalParameters>
</configuration>

would be great. Could you please add this feature!?

[os72]

Are you using the project professionally? I'm trying to garner some support (sponsorship) for it..

[stephanpelikan]

We're evaluating Apache Flink which recommends using protobuf. As we're using Maven I found your plugin useful. Anyway, if we start to rely on it I could ask my supervisor. Until then I also can provide a pull request to support your project.

[nwbirnie]

I just ran into this as well.

The latest protoc RC (3.15.0-rc1) supports proto3 optional without requiring the command line flag.

[JHahnHRO]

Nevertheless would it be very useful to have a way to specify additional command line parameters for the protoc invocation.