Compatibility error on adding sub message type in existing proto file

[Komal Kamble]

Hello ProtocolBufferSupport team,

If I have a proto file with multiple sub-message types defined and If I want to add more sub-message types in the same file I am getting BACKWARD and FORWARD compatibility errors.

I am using com.github.os72:protoc-jar-maven-plugin:3.11.4 plugin in java module to compile proto files and kafka-protobuf-provider:6.1.6 for ProtobufSchema object. 

The query is getting compatibility errors is it correct behavior or not?

I didn't find any documentation in protocol-buffer user guide regarding adding more sub-message types in the existing proto file. 

Could you please help me to understand the standard behavior of the protocol buffer? 

[Adam Cozzette]

Adding more message types to the proto file is fine and has no compatibility issues. Can you say more about the error you're getting?

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[Komal Kamble]

Hello Adam Cozzette,

We are getting Found incompatibility change error of type MESSAGE_REMOVED.

On 02-Nov-2022, at 11:41 PM, Adam Cozzette <acoz...@google.com> wrote:



[Adam Cozzette]

I don't think we maintain any code that returns that kind of error. Do you know where that error is coming from? Is it from some external protobuf compatibility checker?

[Robert Yokota]

Hi,

I believe this is coming from the Confluent compatibility checker.  (I work for Confluent.)

A forward compatibility check is just a backward compatibility check with the arguments reversed.  Since removing a message is not backward compatible, adding a message is not forward compatible.

Hope that helps,

Robert

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[Komal Kamble]

Hello Robert,

Could you please elaborate on reason of having check for message_removed? 

Adding new message doesn’t mean compatibility is lost. 

Sent from my iPhone

On 04-Dec-2022, at 9:41 AM, Robert Yokota <rayo...@gmail.com> wrote:



[Robert Yokota]

Hi Komal,

Forward compatibility is broken as older consumers won't understand the new message.

Regards,

Robert

[Marc Gravell]

That is ... contextual, though; an unexpected sub-message can still, depending on the implementation, be round-tripped and potentially even inspected via reflection. It won't usually *break* code, just like adding any new field. It really depends how strict you're being in you'd definitions of compatibility.

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