fix: convert numeric types inside array/map union branches in Avro se…

[sagarkancharla19]

convertUnionField only handled primitive and named-schema (record, enum,
fixed) union branches. A branch of type array or map fell through to the
"return as-is" fallback, so the float64 values produced by the JSON
round-trip were never converted to int32/int64 for the nested int/long
fields inside the array/map elements.

As a result, any schema shaped like
{"name": "lines", "type": ["null", {"type": "array", "items": {...int fields...}}]}
failed to serialize with:
avro: unknown union type double

Recurse into array/map union branches via
convertFloat64ToIntForIntegerFields and return the value unwrapped,
since hamba/avro resolves unnamed composite branches by Go type.

fixes #408

[sagarkancharla19]

@mostafa please review.

[mostafa]

Review

The diagnosis is right, and this is the correct layer to fix #408.

["null","int"] itself already works in convertUnionField (see TestConvertUnionFieldPrimitiveInt). The failure in #408 is the parent field:

{"name": "lines", "type": ["null", {"type": "array", "items": {… int unions …}}]}

convertUnionField only handled primitives and named types, so the array/map branch fell through as-is. Nested float64 values from the JSON round-trip never became int32/int64, and hamba reported unknown union type double / float64 is unsupported for Avro int. Recursing with convertFloat64ToIntForIntegerFields and returning the value unwrapped matches how hamba resolves unnamed composites.

Please don't merge yet.

Blocking

1. No tests. This needs coverage in avro_conversion_test.go for the #408 shape, at least:

   • ["null", {"type":"array","items": record with ["null","int"]}] + bare lineNumber: 1
   • the same with wrapped {"int": 1}
   • ["null", {"type":"map","values":"int"}] (and/or a map of records with int unions)
   • a full AvroSerde.Serialize round-trip, not only convertUnionField

   Existing tests already cover plain arrays/maps and primitive unions. The missing case is those types as a union branch.

2. gofmt. The new block is space-indented; the rest of the file is tabs. CI lint will fail. Run gofmt (or golangci-lint fmt) on pkg/kafka/avro.go.

Non-blocking

• Link the PR to #408 (Fixes #408) if that is the intended close.
• Swallowing convertFloat64ToIntForIntegerFields errors with continue matches the named-schema path. If the only non-null branch is the array/map, a real conversion error (e.g. 1.5 for int) becomes "return as-is" and a later hamba error. Fine for consistency; returning the error would be clearer when there is no other branch.
• First matching []any / map[string]any wins. Ambiguous unions like ["null", array<int>, array<string>] can pick the wrong branch. Same first-match pattern as primitives; worth a comment if we keep it.

After tests + gofmt this looks good to merge.

[mostafa]

@sagarkancharla19 Will you address this? Or do you want me to take it from here?

[mostafa]

I'll fix them today.

[mostafa]

@sagarkancharla19 Thank you for your contribution.

I made some changes and will merge it now.