polsinello opened a new pull request, #27999:
URL: https://github.com/apache/flink/pull/27999
## What is the purpose of the change
In embedded (thread) mode, Pemja's JNI bridge auto-converts Python
`datetime`/`date`/`time` objects to `java.sql.Timestamp`/`Date`/`Time`, but
Flink's `ExternalSerializer` and `DataFormatConverters.RowConverter` expect the
modern `java.time.*` bridge classes (`LocalDateTime`, `LocalDate`, `LocalTime`,
`Instant`). This mismatch causes `ClassCastException` at serialization
boundaries for any UDF that returns or receives temporal types. Process mode is
unaffected because its Beam-based `runnerOutputTypeSerializer` resolves to the
correct `java.time.*` serializers via `LegacyTypeInfoDataTypeConverter`.
This patch fixes several related type-conversion bugs in the embedded Python
execution path so that all Flink-supported types work correctly in thread mode.
## Brief change log
- Add bridge-aware `DataConverter` implementations for all temporal types
(`TIMESTAMP`, `DATE`, `TIME`, `TIMESTAMP_LTZ`) on both the Table API
(`PythonTypeUtils` in `flink-table-runtime`) and DataStream (`PythonTypeUtils`
in `flink-streaming-java`) paths
- Replace `IdentityDataConverter` for temporal types where it silently
passed `java.sql.*` objects through without conversion
- Fix `ROW`/`TUPLE` buffer reuse in `ArrayDataConverter` that caused
silent data corruption in `ARRAY<ROW<...>>` results
- Widen numeric `DataConverter` generics from `Long`/`Double` to `Number`
to avoid bridge-method `ClassCastException` when Pemja returns
`Integer`/`Float` for small values
- Cache the original Java `ExternalTypeInfo` in the Python
`ExternalTypeInfo` wrapper to prevent lossy `DECIMAL` precision round-trips
through legacy `TypeInfo` conversion
## Verifying this change
This change is already covered by existing tests — the existing PyFlink
Table API and DataStream test suites exercise all affected type paths.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): no
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: no
- The serializers: no (fixes type conversion *before* values reach the
serializer)
- The runtime per-record code paths (performance sensitive): yes — the
embedded Python UDF execution path now performs explicit type conversions for
temporal/numeric types instead of relying on identity pass-through. The
overhead is minimal (one `java.time.*` factory call per value).
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
- The S3 file system connector: no
## Documentation
- Does this pull request introduce a new feature? no
- If yes, how is the feature documented? not applicable
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