RemoveIdentityProjectionsBelowProjection.java

/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.facebook.presto.sql.planner.iterative.rule;

import com.facebook.presto.matching.Capture;
import com.facebook.presto.matching.Captures;
import com.facebook.presto.matching.Pattern;
import com.facebook.presto.spi.plan.ProjectNode;
import com.facebook.presto.sql.planner.iterative.Rule;
import com.facebook.presto.sql.relational.ProjectNodeUtils;
import com.google.common.collect.ImmutableList;

import static com.facebook.presto.matching.Capture.newCapture;
import static com.facebook.presto.sql.planner.plan.Patterns.project;
import static com.facebook.presto.sql.planner.plan.Patterns.source;

public class RemoveIdentityProjectionsBelowProjection
        implements Rule<ProjectNode>
{
    private static final Capture<ProjectNode> CHILD = newCapture();
    private static final Pattern<ProjectNode> PATTERN = project().with(source().matching(project().matching(ProjectNodeUtils::isIdentity).capturedAs(CHILD)));

    @Override
    public Pattern<ProjectNode> getPattern()
    {
        return PATTERN;
    }

    @Override
    public Result apply(ProjectNode node, Captures captures, Context context)
    {
        ProjectNode child = captures.get(CHILD);
        return Result.ofPlanNode(node.replaceChildren(ImmutableList.of(child.getSource())));
    }
}