AVRO-2518: Ruby Avro doesn't validate enum fields with default values

[kyleboyer-optum]

Jira

• My PR addresses the following Avro Jira issues and references them in the PR title. For example, "AVRO-1234: My Avro PR"
  • https://issues.apache.org/jira/browse/AVRO-2518

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  • test_enum_field_default

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  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • No new functionality - bug fix

[tjwp]

Thank you for the contribution.

I'm not surprised that the support for enum defaults is lacking in the Ruby implementation. The implementations in different languages do not move in lock-step.

I'm not convinced that this is the right change to make to the Ruby implementation. There is no other reference to defaults for any other field types in the SchemaValidator class. This class is used to verify that a datum is compatible with a writer's schema.

Defaults are used during resolution, and the default comes from the reader's schema if a value is not supplied, or in the case of an enum if the symbol is not part of the reader's schema.

I suspect there is a larger set of changes need to support enum defaults in the Ruby implementation.

[tjwp]

I don't think this is the right place in the code to special case the handling of enum. There is a line in validate_simple that handles enum. I think that any modification should be there:

https://github.com/apache/avro/pull/618/files#diff-a1c5bb746106005a7d7ef59a2b973cdbL137

[kyleboyer-optum]

@tjwp Thanks for the feedback! After debugging the (newly added in my PR) test, I traced it down to this point. The issue with validate_simple is that in the case of this test, the default is defined at the field level, which would get removed/stripped when recursively trying to validate the field.type in the next nested recursive iteration. I'm not 100% sure, but are you asking/would it be better/merge-able to refactor those two functions to call validate_simple against enums(maybe with an overloaded function)?

{
  "type": "record",
  "name": "enum_field_default",
  "fields": [
    {
      "name": "msg",
      "type": "string"
    },
    {
      "name": "logClass",
      "type": {
        "type": "enum",
        "name": "logClass",
        "symbols": [
          "UNCATEGORIZED",
          "E1",
          "E2",
          "E3",
          "E4",
          "E5",
          "E6",
          "E7",
          "E8",
          "E9",
          "E10"
        ]
      },
      "default": "UNCATEGORIZED"
    }
  ]
}