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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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/*
 * Copyright 2014 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.common.collect.HashBasedTable;
import com.google.common.collect.Table;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.Node;
import java.util.HashSet;
import java.util.Set;

/**
 * Renames declarations and references in function bodies to avoid shadowing
 * names referenced in the parameter list, in default values or computed properties.
 */
public final class Es6RenameVariablesInParamLists extends AbstractPostOrderCallback
    implements HotSwapCompilerPass {

  private final AbstractCompiler compiler;
  private static final FeatureSet transpiledFeatures =
      FeatureSet.BARE_MINIMUM.with(Feature.DEFAULT_PARAMETERS, Feature.COMPUTED_PROPERTIES);

  public Es6RenameVariablesInParamLists(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    // Arrow functions without blocked body cannot have declarations in the body
    if (!n.isFunction() || !n.getLastChild().isBlock()) {
      return;
    }

    Node paramList = n.getSecondChild();
    final CollectReferences collector = new CollectReferences();
    NodeTraversal.traverse(compiler, paramList, new NodeTraversal.AbstractPreOrderCallback() {
      @Override
      public final boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
        if (parent == null) {
          return true;
        }

        if ((parent.isDefaultValue() && n == parent.getLastChild())
            || (parent.isComputedProp() && n == parent.getFirstChild())) {
          NodeTraversal.traverse(compiler, n, collector);
          return false;
        }
        return true;
      }
    });

    Node block = paramList.getNext();
    SyntacticScopeCreator creator = new SyntacticScopeCreator(compiler);
    Scope fScope = creator.createScope(n, t.getScope());
    Scope fBlockScope = creator.createScope(block, fScope);
    Table renameTable = HashBasedTable.create();
    for (Var var : fBlockScope.getVarIterable()) {
      String oldName = var.getName();
      if (collector.currFuncReferences.contains(oldName)
          && !renameTable.contains(fBlockScope.getRootNode(), oldName)) {
        renameTable.put(fBlockScope.getRootNode(),
            oldName, oldName + "$" + compiler.getUniqueNameIdSupplier().get());
      }
    }
    new NodeTraversal(
            compiler, new Es6RenameReferences(renameTable), new SyntacticScopeCreator(compiler))
        .traverseInnerNode(block, block.getParent(), fScope);
  }

  @Override
  public void process(Node externs, Node root) {
    TranspilationPasses.processTranspile(compiler, root, transpiledFeatures, this);
  }

  @Override
  public void hotSwapScript(Node scriptRoot, Node originalRoot) {
    TranspilationPasses.hotSwapTranspile(compiler, scriptRoot, transpiledFeatures, this);
  }

  /**
   * Collects all references in a naive way.
   */
  private static class CollectReferences extends NodeTraversal.AbstractPostOrderCallback {

    private final Set currFuncReferences = new HashSet<>();

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (!NodeUtil.isReferenceName(n)) {
        return;
      }
      currFuncReferences.add(n.getString());
    }
  }
}