SPARK-53968 SQLViewSuite: decimal arithmetic returns ~10x smaller values through view CTE on Spark 4.1.1

[andygrove]

Describe the bug

The new Spark 4.1 test SPARK-53968 reading the view after allowPrecisionLoss is changed in SQLViewSuite fails with Comet enabled. The test stores DECIMAL(38, 18) values and computes unit_price + COALESCE(shipping_price, 0) through a CTE wrapped in a view. Comet returns values approximately 10x smaller than expected:

Row	Expected	Actual (with Comet)
part1	100.00000000000000000	10.00000000000000000
part2	100.00000000000000000	10.00000000000000000
part3	300.23000000000000000	30.02300000000000000

The plan involves CometBroadcastHashJoin → CometProject(unit_price + COALESCE(shipping_price, 0E-18)) → CometExchange(rangepartitioning) → CometSort.

Steps to reproduce

Run Spark 4.1.1's SQLViewSuite with Comet enabled. The reproducer is the test body itself (see sql/core/src/test/scala/org/apache/spark/sql/execution/SQLViewSuite.scala SPARK-53968 reading the view after allowPrecisionLoss is changed).

Expected behavior

unit_price + shipping_price should match Spark's result (100, 100, 300.23).

Workaround

The test is currently tagged IgnoreComet(...) in dev/diffs/4.1.1.diff.

Additional context

PR #4093 enables Spark 4.1.1 in the Spark SQL Tests workflow. The 10x discrepancy and the DECIMAL(38, 18) schema strongly suggest a precision/scale handling bug in Comet's decimal addition or in the view-resolution path that drops 1 digit of scale.