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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2021 The Closure Compiler Authors.
 *
 * 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.google.javascript.jscomp;

import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.Node;

/** Replaces the ES2020 `||=`, `&&=`, and `??=` operators. */
public final class RewriteLogicalAssignmentOperatorsPass
    implements NodeTraversal.Callback, CompilerPass {

  private final AbstractCompiler compiler;
  private final RewriteLogicalAssignmentOperatorsHelper rewriteLogicalAssignmentOperatorsHelper;

  public RewriteLogicalAssignmentOperatorsPass(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.rewriteLogicalAssignmentOperatorsHelper =
        new RewriteLogicalAssignmentOperatorsHelper(
            compiler, compiler.createAstFactory(), compiler.getUniqueIdSupplier());
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, this);
    TranspilationPasses.maybeMarkFeatureAsTranspiledAway(
        compiler, root, Feature.LOGICAL_ASSIGNMENT);
  }

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    if (n.isScript()) {
      FeatureSet scriptFeatures = NodeUtil.getFeatureSetOfScript(n);
      // runs only if logical assignment present
      return scriptFeatures == null || scriptFeatures.contains(Feature.LOGICAL_ASSIGNMENT);
    }
    return true;
  }

  @Override
  public void visit(NodeTraversal t, Node logicalAssignment, Node parent) {
    switch (logicalAssignment.getToken()) {
      case ASSIGN_OR:
      case ASSIGN_AND:
      case ASSIGN_COALESCE:
        rewriteLogicalAssignmentOperatorsHelper.visitLogicalAssignmentOperator(
            t, logicalAssignment);
        break;
      default:
        break;
    }
  }
}