[SPARK-26706] Fix Cast$mayTruncate for bytes

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Resolved
• Affects Version/s: 1.6.3, 2.0.2, 2.1.3, 2.2.3, 2.3.2, 2.4.0
• Fix Version/s: 2.3.3, 2.4.1
• Component/s: SQL
• Labels: correctness
• Assignee: Anton Okolnychyi
• Reporter: Anton Okolnychyi
• Created: 23/Jan/19 13:48
• Updated: 24/Jan/19 06:01
• Resolved: 24/Jan/19 06:01

Description

The logic in Cast$mayTruncate is broken for bytes.

Right now, mayTruncate(ByteType, LongType) returns false while mayTruncate(ShortType, LongType) returns true. Consequently, spark.range(1, 3).as[Byte] and spark.range(1, 3).as[Short] will behave differently.

Potentially, this bug can lead to silently corrupting someone's data.

// executes silently even though Long is converted into Byte
spark.range(Long.MaxValue - 10, Long.MaxValue).as[Byte]
  .map(b => b - 1)
  .show()
+-----+
|value|
+-----+
|  -12|
|  -11|
|  -10|
|   -9|
|   -8|
|   -7|
|   -6|
|   -5|
|   -4|
|   -3|
+-----+
// throws an AnalysisException: Cannot up cast `id` from bigint to smallint as it may truncate
spark.range(Long.MaxValue - 10, Long.MaxValue).as[Short]
  .map(s => s - 1)
  .show()

Issue Links

• links to: GitHub Pull Request #23632