rayokota opened a new pull request, #4019:
URL: https://github.com/apache/avro/pull/4019
…ility
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## What is the purpose of the change
When a reader swaps or rotates field names using aliases (for example `b`
aliased `a`, and `a` aliased `b`), `SchemaCompatibility` throws
`AvroRuntimeException` ("Reader record
field b ... matches multiple fields in writer record schema"). The decoder
reads the same schemas correctly. This fixes AVRO-XXXX.
`lookupWriterField` collects the writer field with the reader field's own
name, plus each writer field named by one of its aliases, and throws when it
finds more than one. The
decoder instead goes through `Schema.applyAliases`, which renames the
writer's `a` to `b` and its `b` to `a`, so each reader field reads the writer
field its alias names. Record
name swaps already work in both, because the checker compares type names
at each location.
The record-fields check now uses a new package-private
`lookupWriterField(writer, reader, readerField)`, which can see the whole
reader record. If the writer field with the
reader field's own name is claimed by another reader field's alias, the
reader field takes the writer field its own alias names. That is exactly when
`applyAliases` renames that
writer field away.
Every other case falls through to the existing `lookupWriterField(Schema,
Field)`, whose behavior is unchanged:
- A reader field aliasing a writer field that no other alias frees still
throws. The decoder fails there too, with "Duplicate field".
- Renaming a field and reusing its old name for a new field is checked as
before.
## Verifying this change
This change added tests to `TestSchemaCompatibility`:
- A two-field swap is compatible, and decoding with `GenericDatumReader`
gives the same pairing.
- A three-field rotation is compatible.
- A swap inside a nested record is compatible.
- Swapped fields are compared against the writer fields their aliases
name, so a type swapped as well is reported as `TYPE_MISMATCH`.
- A reader field aliasing a writer field that no other alias frees still
throws.
The swap and rotation tests fail without the change. All
`TestSchemaCompatibility*` tests pass (82).
## Documentation
- Does this pull request introduce a new feature? no
- If yes, how is the feature documented? not applicable
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