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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 2009 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 static com.google.common.base.Preconditions.checkState;

import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;
import java.util.HashSet;
import java.util.Set;

/**
 * External references of the form: "window['xx']" indicate names that must
 * be reserved when variable renaming to avoid conflicts.
 */
class GatherRawExports extends AbstractPostOrderCallback
    implements CompilerPass {

  private final AbstractCompiler compiler;

  // TODO(johnlenz): "goog$global" should be part of a coding convention.
  // Note: GatherRawExports runs after property renaming and
  // collapse properties, so the two entries here protect goog.global in the
  // two common cases "collapse properties and renaming on" or both off
  // but not the case where only property renaming is on.
  private static final String[] GLOBAL_THIS_NAMES = {
    "window", "top", "goog$global", "goog.global" };

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

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

  @Override
  public void process(Node externs, Node root) {
    checkState(compiler.getLifeCycleStage().isNormalized());
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    Node sibling = n.getNext();
    if (sibling != null && sibling.isString() && NodeUtil.isGet(parent)
        && isGlobalThisObject(t, n)) {
      exportedVariables.add(sibling.getString());
    }
  }

  private static boolean isGlobalThisObject(NodeTraversal t, Node n) {
    if (n.isThis()) {
      return t.inGlobalHoistScope();
    } else if (n.isQualifiedName()) {
      int items = GLOBAL_THIS_NAMES.length;
      for (int i = 0; i < items; i++) {
        if (n.matchesQualifiedName(GLOBAL_THIS_NAMES[i])) {
          return true;
        }
      }
    }
    return false;
  }

  public Set getExportedVariableNames() {
    return exportedVariables;
  }
}