[CALCITE-6089] EnumerableSortedAggregate fails with ClassCastException: class X cannot be cast to class org.apache.calcite.runtime.FlatLists$ComparableList

[1fanwang]

Jira Link

CALCITE-6089

Changes Proposed

Counting rows over a UNION ALL failed at runtime when the sorted aggregate was
used:

java.lang.ClassCastException: class java.lang.Integer cannot be cast to class
org.apache.calcite.runtime.FlatLists$ComparableList

The query now returns c=4.

The aggregate has no group key. The rule used to convert it anyway, and
comparing the zero-length keys threw. CALCITE-6087 made the rule decline an
empty group set, so no sorted aggregate is produced, the planner uses the
regular aggregate, and the query succeeds. That fix therefore closed this issue
too, so this PR adds only the regression tests requested when #5202 merged.

Two tests, following the pattern that patch established. One forces the sorted
rule and asserts the planner now rejects the plan; the other runs the query with
the usual rule set and asserts the result.

Testing

Running the suite on this branch, which is current main plus the two new tests:

$ ./gradlew :core:test --tests '*EnumerableSortedAggregateTest'
15 completed, 0 failed, 0 skipped
BUILD SUCCESSFUL

Reverting only the one-line rule change from CALCITE-6087, and keeping the new
tests, reproduces the original failure:

$ git checkout bd65b15fc6^ -- core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableSortedAggregateRule.java
$ ./gradlew :core:test --tests '*EnumerableSortedAggregateTest.sortedAggCountUnion*'
FAILURE sortedAggCountUnionRejectsEmptyGroupSet()
  but: was "java.sql.SQLException: Error while executing SQL ...:
  class java.lang.Integer cannot be cast to class
  org.apache.calcite.runtime.FlatLists$ComparableList"
2 completed, 1 failed

Are there any user-facing changes?

No. Tests only.

[mihaibudiu]

I approved, but please simplify the useless comments.

[mihaibudiu]

I don't think we care about what used to happen previously. We are not keeping a log of all past bugs.

[mihaibudiu]

please squash the commits for merging

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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