[SPARK-9286] [SQL] Methods in Unevaluable should be final and AlgebraicAggregate should extend Unevaluable.

[JoshRosen]

This patch marks the Unevaluable.eval() and UnevaluablegenCode() methods as final and fixes two cases where they were overridden. It also updates AggregateFunction2 to extend Unevaluable.

[JoshRosen]

Hold on one sec... going to update this so that AggregateFunction2 also extends Unevaluable.

[JoshRosen]

Did we need this?

[yhuai]

I think we do not need it.

[JoshRosen]

/cc @yhuai for review.

[yhuai]

AggregateFunction2 should extend Unevaluable. => AlgebraicAggregate should extend Unevaluable.

[JoshRosen]

Good catch; updated.

[SparkQA]

Test build #38267 has finished for PR 7627 at commit 65329c2.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • abstract class AggregateFunction1 extends LeafExpression with Serializable

[yhuai]

LGTM. Merging it to master.

[SparkQA]

Test build #38275 has finished for PR 7627 at commit 8d9ed22.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • abstract class AlgebraicAggregate extends AggregateFunction2 with Serializable with Unevaluable
  • abstract class AggregateFunction1 extends LeafExpression with Serializable