fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/MergeGenerates.java

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//   http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.doris.nereids.rules.rewrite;

import org.apache.doris.nereids.rules.Rule;
import org.apache.doris.nereids.rules.RuleType;
import org.apache.doris.nereids.trees.expressions.Slot;
import org.apache.doris.nereids.trees.expressions.functions.Function;
import org.apache.doris.nereids.trees.plans.Plan;
import org.apache.doris.nereids.trees.plans.logical.LogicalGenerate;

import com.google.common.collect.Lists;

import java.util.List;
import java.util.Set;

/**
 * merge two generate into one if the top one's input slot with no bottom's generate output.
 */
public class MergeGenerates extends OneRewriteRuleFactory {
    @Override
    public Rule build() {
        return logicalGenerate(logicalGenerate()).then(top -> {
            LogicalGenerate<Plan> bottom = top.child();
            Set<Slot> topGeneratorSlots = top.getInputSlots();
            if (bottom.getGeneratorOutput().stream().anyMatch(topGeneratorSlots::contains)) {
                // top generators use bottom's generator's output, cannot merge.
                return top;
            }
            List<Function> generators = Lists.newArrayList(bottom.getGenerators());
            generators.addAll(top.getGenerators());
            List<Slot> generatorsOutput = Lists.newArrayList(bottom.getGeneratorOutput());
            generatorsOutput.addAll(top.getGeneratorOutput());
            return new LogicalGenerate<>(generators, generatorsOutput, bottom.child());
        }).toRule(RuleType.MERGE_GENERATES);
    }
}