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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.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.rhino.Node;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.logging.Logger;

/**
 * Gives anonymous function names that are optimized to be small and provides a
 * mapping back to the original 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 $qv(str) {
 * }
 *
 * And there will be mapping from $qv to goog.string.htmlEscape
 */
class NameAnonymousFunctionsMapped implements CompilerPass {

  private static final Logger logger =
      Logger.getLogger(NameAnonymousFunctionsMapped.class.getName());

  static final char PREFIX = '$';
  static final String PREFIX_STRING = "$";

  private final AbstractCompiler compiler;
  private final NameGenerator nameGenerator;
  private final VariableMap previousMap;
  private final Map renameMap;

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

  NameAnonymousFunctionsMapped(
      AbstractCompiler compiler, VariableMap previousMap) {
    this.compiler = compiler;
    Set reserved =
        previousMap != null
            ? previousMap.getNewNameToOriginalNameMap().keySet()
            : ImmutableSet.of();
    this.nameGenerator = new DefaultNameGenerator(reserved, PREFIX_STRING, null);
    this.previousMap = previousMap;
    this.renameMap = new HashMap<>();
  }

  @Override
  public void process(Node externs, Node root) {
    AnonymousFunctionNamingCallback namingCallback =
        new AnonymousFunctionNamingCallback(new MappedFunctionNamer());
    NodeTraversal.traverse(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 MappedFunctionNamer
      implements AnonymousFunctionNamingCallback.FunctionNamer {
    static final char DELIMITER = '.';

    @Override
    public final String getName(Node node) {
      switch (node.getToken()) {
        case NAME:
        case STRING:
        case STRING_KEY:
          return node.getString();
        case COMPUTED_PROP:
          return getName(node.getFirstChild());
        default:
          return compiler.toSource(node);
      }
    }

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

    String getAlternateName(String name) {
      String newName = renameMap.get(name);
      if (newName == null) {
        // Use the previously used name, if possible.
        if (previousMap != null) {
          newName = previousMap.lookupNewName(name);
        }
        if (newName == null) {
          // otherwise generate a new name.
          newName = nameGenerator.generateNextName();
        }
        renameMap.put(name, newName);
      }
      return newName;
    }

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

  /**
   * Gets the function renaming map (the "answer key").
   *
   * @return A mapping from original names to new names
   */
  VariableMap getFunctionMap() {
    return new VariableMap(ImmutableMap.copyOf(renameMap));
  }
}