AVRO-4133: Support default enum value in Protobuf to Avro

[zenfenan]

What is the purpose of the change

This PR creates enum Schema with the default symbol when converting Protobuf descriptor to Avro schema.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Documentation

• Does this pull request introduce a new feature? (yes)
• If yes, how is the feature documented? (not applicable)

[martin-g]

https://protobuf.dev/programming-guides/proto3/#default - 👍🏻

[zenfenan]

@martin-g Could you also merge this?

[nandorKollar]

@zenfenan Would you mind add an extra test case to demonstrate this change? It seems that at the moment nothing tests enum schema conversions, I think TestProbuf would be a good place for an extra test case. It appears, that we didn't handle default tags in the past either, like the example in test.proto: optional A enum = 16 [default = Z];. Probably we should raise a separate Jira to handle default tags properly.

[opwvhk]

The change itself looks good, but it lacks a test case.
Preferably with the link @martin-g provided: https://protobuf.dev/programming-guides/proto3/#default

[zenfenan]

@nandorKollar & @opwvhk

Thanks for your reviews! I realised that you can actually have default value in your protobuf schema until proto2. It is only removed in proto3. Refer:

• https://protobuf.dev/programming-guides/proto2/#enum-default
• https://protobuf.dev/programming-guides/proto3/#enum-default

So I updated the code to handle that, and also added a test (with new proto3 schema). Let me know if the commits need to be squashed into a single commit.

BTW, the CodeQL violations are on the protobuf generated code. I couldn't find any exclusion config in the project. Let me know if this needs to be handled or not!

[opwvhk]

I like this test. Especially the overridden default. What i don't see, however, is the field default values in the first two cases.

An opinion on the CodeQL comments on generated code: as its generated code, by a generator outside or control, I place little to no importance to these style comments. I'd mark them as "won't fix".

[zenfenan]

@opwvhk I am unable to mark the CodeQL warnings as "Won't fix". I also don't have the permission to merge. Possibly because I am not part of the committers list for this repo.

If there is nothing else pending, could you resolve the CodeQL warnings and also merge the PR? Thanks!