[jira] [Created] (CALCITE-5705) Generalize RemoveEmptySingleRule to work with arbitrary relations and pruning configurations

["Stamatis Zampetakis (Jira)" <ji...@apache.org>]

Stamatis Zampetakis created CALCITE-5705:
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             Summary: Generalize RemoveEmptySingleRule to work with arbitrary relations and pruning configurations
                 Key: CALCITE-5705
                 URL: https://issues.apache.org/jira/browse/CALCITE-5705
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Stamatis Zampetakis
            Assignee: Stamatis Zampetakis
             Fix For: 1.35.0


Currently [RemoveEmptySingleRule|https://github.com/apache/calcite/blob/b0b27e8872b33c5ab203e0e2365d267a594c80be/core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java#LL285C23-L285C44] can only transform {{SingleRel}} relations to empty. However, the logic inside the {{matches}} method is at the most part capable of handling any kind of relation including those that have multiple children.

By generalizing the {{RemoveEmptySingleRule}} to work with arbitrary relations we can refactor other pruning rules such as those created by [CorrelateLeftEmptyRuleConfig|https://github.com/apache/calcite/blob/b0b27e8872b33c5ab203e0e2365d267a594c80be/core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java#L588] without the need for creating more classes and duplicating code.

Moreover by changing the constructor to accept {{PruneEmptyRule.Config}} instead of {{RemoveEmptySingleRuleConfig}} we can reduce code duplication further since configurations such as {{ZeroMaxRowsRuleConfig}} and {{SortFetchZeroRuleConfig}} could be modified to create instances of {{RemoveEmptySingleRule}}.

This is mainly a refactoring to simplify pruning rules and remove duplicate logic. The change is fully backwards compatible.



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