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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 2004 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.rhino.Node;
import java.util.logging.Logger;

/**
 * Gives anonymous function names. This makes it way easier to debug because
 * debuggers and stack traces use the function names. So if you have
 *
 * goog.string.htmlEscape = function(str) {
 * }
 *
 * It will become
 *
 * goog.string.htmlEscape = function $goog$string$htmlEscape$(str) {
 * }
 *
 */
class NameAnonymousFunctions implements CompilerPass {
  private static final Logger logger = Logger.getLogger(
      NameAnonymousFunctions.class.getName());

  static final char DELIMITER = '$';

  private final AbstractCompiler compiler;

  private int namedCount = 0;
  private int bytesUsed = 0;

  NameAnonymousFunctions(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    AnonymousFunctionNamingCallback namingCallback =
        new AnonymousFunctionNamingCallback(new AnonymousFunctionNamer());
    NodeTraversal.traverseEs6(compiler, root, namingCallback);
    logger.fine("Named " + namedCount + " anon functions using " +
        bytesUsed + " bytes");
  }

  /**
   * Names anonymous functions. The function names don't have to be globally
   * unique or even locally unique. We make them somewhat unique because of a
   * bug in IE (and there may be other bugs we haven't found). See unit test for
   * more info.
   */
  private class AnonymousFunctionNamer
      implements AnonymousFunctionNamingCallback.FunctionNamer {
    private final NodeNameExtractor nameExtractor;

    AnonymousFunctionNamer() {
      this.nameExtractor = new NodeNameExtractor(DELIMITER);
    }

    /**
     * Returns a likely not conflicting name to make IE happy. See unit test
     * for more info.
     */
    private String getLikelyNonConflictingName(String name) {
      return DELIMITER + name + DELIMITER;
    }

    @Override
    public final String getName(Node node) {
      return nameExtractor.getName(node);
    }

    @Override
    public final void setFunctionName(String name, Node fnNode) {
      Node fnNameNode = fnNode.getFirstChild();
      String uniqueName = getLikelyNonConflictingName(name);
      fnNameNode.setString(uniqueName);
      compiler.reportChangeToEnclosingScope(fnNameNode);
      namedCount++;
      bytesUsed += uniqueName.length();
    }

    @Override
    public final String getCombinedName(String lhs, String rhs) {
      return lhs + DELIMITER + rhs;
    }
  }
}