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https://issues.apache.org/jira/browse/SPARK-55681?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wenchen Fan reassigned SPARK-55681:
-----------------------------------
Assignee: Tim Lee
> Singleton DataType equality fails after deserialization
> -------------------------------------------------------
>
> Key: SPARK-55681
> URL: https://issues.apache.org/jira/browse/SPARK-55681
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 4.1.1
> Reporter: Tim Lee
> Assignee: Tim Lee
> Priority: Major
> Labels: pull-request-available
>
> When a singleton DataType (e.g., BinaryType, IntegerType) is deserialized by
> a framework that bypasses readResolve() — such as Kryo with certain
> configurations — a new instance of the class is created instead of returning
> the case object singleton. This non-singleton instance then fails pattern
> matching at every `case BinaryType =>` site in the codebase, because Scala
> case object matching relies on equals(), which defaults to reference equality.
> The failure manifests as silent match fallthrough, leading to errors like:
> {code:java}
> IllegalStateException: The data type 'binary' is not supported in generating
> a writer function... {code}
>
> The issue affects all 14 singleton DataType classes that use the `class +
> case object` pattern without an explicit equals() override:
>
> {code:java}
> BinaryType, BooleanType, ByteType, ShortType, IntegerType, LongType,
> FloatType, DoubleType, DateType, TimestampType, TimestampNTZType, NullType,
> CalendarIntervalType, VariantType {code}
>
> Other DataTypes already handle this correctly:
> # VarcharType, CharType, TimeType, GeometryType, GeographyType — matched by
> type (`case _: XType =>`) rather than value
> # StringType — has custom equals() comparing collationId
> # DecimalType, ArrayType, MapType, StructType — case classes with
> auto-generated equals()
> *Proposed fix:* Override equals() and hashCode() on the 14 affected
> classes:
> {code:java}
> override def equals(obj: Any): Boolean = obj.isInstanceOf[XType]
> override def hashCode(): Int = classOf[XType].getSimpleName.hashCode {code}
> getSimpleName is used because Scala's auto-generated hashCode for 0-arity
> case objects returns productPrefix.hashCode (the simple class name). This
> preserves the original hash values, avoiding any behavioral change for code
> that depends on DataType hashCodes (e.g., HashMap/HashSet lookups,
> canonicalization ordering).
> The change is strictly additive: singleton-to-singleton equality is
> unchanged; only the non-singleton edge case gains correct behavior. Although
> the constructors are private, this is a compile-time guard only –
> serialization frameworks bypass constructors at runtime.
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