fix: ArrayInsert evaluation for null source arrays

[peterxcli]

Which issue does this PR close?

No issue for this, relate to: #4716

Rationale for this change

Comet previously evaluated all ArrayInsert children for the full batch. This differed from Spark, which evaluates arguments left-to-right and does not evaluate the position or inserted item when the source array is NULL.

This caused expressions such as element_at(array(1), 0) to be evaluated even though Spark would short-circuit and return NULL for the row.

This patch uses DataFusion’s evaluate_selection in the native ArrayInsert implementation to skip evaluating pos and item for rows where the source array is NULL. It also adds regression coverage for both array_insert and array_prepend, since Spark rewrites array_prepend to array_insert(..., 1, ...).

What changes are included in this PR?

argument parsing logic in array_insert batch execution.

How are these changes tested?

• ./mvnw test -Dsuites="org.apache.comet.CometSqlFileTestSuite array_prepend" -Dtest=none
• ./mvnw test -Dsuites="org.apache.comet.CometSqlFileTestSuite array_insert" -Dtest=none

[peterxcli]

sorry let me fix the test error.

[andygrove]

Nice fix. The short-circuit logic matches Spark's ArrayInsert.eval exactly, and evaluating src before pos also lines up error precedence with Spark when more than one argument can throw.

One suggestion on test coverage. The new test_array_insert_short_circuit case nicely exercises skipping pos (and item) when src is NULL. There's a second, distinct path that the new && pos_value.is_valid(row) guard on evaluate_item protects: src non-null, pos NULL, and an item that would throw if evaluated. Spark short-circuits item there too (the inner if (value2 != null) check), so it returns NULL rather than raising. It might be worth pinning that down with something like:

statement
INSERT INTO test_array_insert_short_circuit VALUES
  (NULL, 0),
  (array(1), 1),
  (array(1), 2)

query
SELECT array_insert(arr, CAST(NULL AS INT), element_at(array(1), idx))
FROM test_array_insert_short_circuit

Here pos is NULL for every row, so item = element_at(array(1), idx) should never be evaluated, including the idx = 0 and idx = 2 rows that would otherwise throw. Without the pos validity check on evaluate_item this would error, so it guards that branch directly.