timlee0119 opened a new pull request, #54475:
URL: https://github.com/apache/spark/pull/54475
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### What changes were proposed in this pull request?
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Override `equals()` and `hashCode()` on 14 singleton `DataType` classes so
that non-singleton instances compare equal to the case object singletons:
```
BinaryType, BooleanType, ByteType, ShortType, IntegerType, LongType,
FloatType, DoubleType, DateType, TimestampType, TimestampNTZType, NullType,
CalendarIntervalType, VariantType
```
For each type:
```
override def equals(obj: Any): Boolean = obj.isInstanceOf[XType]
override def hashCode(): Int = classOf[XType].getSimpleName.hashCode
```
`getSimpleName` is used because Scala's auto-generated hashCode for 0-arity
case objects returns `productPrefix.hashCode` (the simple class name). This
preserves the exact same hash values, avoiding any change in hash-dependent
code paths.
Other DataTypes did not need this change:
- VarcharType, CharType, TimeType, GeometryType, GeographyType — already
matched by type (case _: XType
=>) across the codebase
- StringType — has custom equals() comparing collationId
- DecimalType, ArrayType, MapType, StructType — case classes with
auto-generated equals()
### Why are the changes needed?
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Scala case object pattern matching (e.g., `case BinaryType =>`) relies on
`equals()`, which for case objects defaults to reference equality. If a
non-singleton instance of a DataType class is created at runtime — through any
serialization framework that bypasses `readResolve()` — every case `BinaryType`
=> match in the codebase silently falls through, leading to errors like ([code
pointer](https://github.com/apache/spark/blob/3e4df1c1c1e1d9f594a6afcf29b3bae05cc8a348/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/InterpretedUnsafeProjection.scala#L241)):
```
IllegalStateException: The data type 'binary' is not supported in generating
a writer function...
```
Although the constructors are private, this is a compile-time guard only —
serialization frameworks
bypass constructors at runtime, so non-singleton instances can be created.
### Does this PR introduce _any_ user-facing change?
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Yes. Before this change, if a non-singleton DataType instance was created
through deserialization, pattern matches like `case BinaryType =>` would
silently fail, leading to non-deterministic runtime errors. After this change,
non-singleton instances are correctly recognized as equal to the singleton, and
pattern matching works as expected.
### How was this patch tested?
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1. Unit test in DataTypeSuite (singleton DataType equality after
deserialization): creates non-singleton instances via reflection for all 14
types, verifies bidirectional equality with singletons, matching hashCode, and
correct PhysicalDataType resolution (no fallthrough to
UninitializedPhysicalType).
2. Also verified that ExpressionSetSuite passes unchanged (its magic
hashCode values are calibrated against IntegerType.hashCode, confirming hash
preservation).
### Was this patch authored or co-authored using generative AI tooling?
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Generated-by: Claude Code (Claude Opus 4.6)
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