raminqaf opened a new pull request, #29279:
URL: https://github.com/apache/flink/pull/29279
## What is the purpose of the change
In the Table API, a `CAST` to a target written with `.notNull()` was planned
as `NOT NULL` even when the input may be null. The `CAST` type strategy already
derives a nullable result, but `CastConverter` built the RexNode from the
literal target type. The optimizer trusted the wrong `NOT NULL` and could fold
null checks away. For example, `$("i").cast(BIGINT().notNull())` over a
nullable `i` followed by `.filter($("c").isNull())` returned no rows instead of
the null row.
FLINK-40672 fixed this only for a top-level `VARIANT` input. Nested inputs
such as `ARRAY<VARIANT>` and plain nullable scalars were still affected. SQL is
not affected: a SQL `CAST` cannot declare `NOT NULL` on the target, and
`SqlCastFunction.deriveType` takes the nullability from the input.
## Brief change log
- `CastConverter` uses the resolved output type of the call instead of the
literal target type, which aligns the Table API with SQL for all casts.
- The `cast()` Javadoc states that the top-level nullability of the target
type is ignored.
## Verifying this change
This change added tests and can be verified as follows:
- Added cases to `ExpressionConverterTest` for a nullable input cast to a
`NOT NULL` target, a nested `VARIANT` input, and a `NOT NULL` input cast to a
nullable target. All three fail without the fix.
- Existing planner plan, expression, cast and runtime Table API tests pass
unchanged.
## 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. Only the Javadoc of `cast()` changes.
- The serializers: no
- The runtime per-record code paths (performance sensitive): no
- 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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