IssueTracker

Problem you have encountered:

I have a Pub/Sub topic that uses Protobuf as its schema. I cannot create new revision of schema with a value added to the enum in that field.

What you expected to happen:

We can add the value to enum.

Steps to reproduce:

1. Create a topic schema with the following schama as the initial revision:

syntax = "proto3";
package com.example;

message UserAuthLog {
  enum Method {
    METHOD_UNKNOWN = 0;
    PASSWORD = 1;
  }
  Method method = 1;
}

2. Press "create revision" button, change the schema as follows and press the "commit" button:.

syntax = "proto3";
package com.example;

message UserAuthLog {
  enum Method {
    METHOD_UNKNOWN = 0;
    PASSWORD = 1;
    SSO = 2; // added
  }
  Method method = 1;
}

3. Produces error:

The schema definition is incompatible with a previous revision: 41dcefb9. com.example.UserAuthLog.SSO = 2 is missing in com.example.UserAuthLog.Method.

Other information (workarounds you have tried, documentation consulted, etc):

In our system, we write data to BigQuery from subscriber.

Assuming that enum is equivalent to int32 in the binary representation of protobuf. https://protobuf.dev/programming-guides/encoding/#structure

Therefore, it is possible to publish the message with method as int32 and the value as 999999, and when we experimented with this, I observed that the default value of 0 is written to BigQuery (reasonable behaiviour).

The error message about incompatibility with older versions is correct, but I think not being able to add values to an enumerated type would be much less extensible.

I think falling back to default for unknown enum values in older versions is enough

We take the workaround of changing the method field to int32.