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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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;

import com.google.javascript.rhino.Node;

/**
 * Scope contains information about a variable scope in JavaScript.
 * Scopes can be nested, a scope points back to its parent scope.
 * A Scope contains information about variables defined in that scope.
 *
 * @see NodeTraversal
 */
public abstract class Scope extends AbstractScope {

  Scope(Node rootNode) {
    super(rootNode);
  }

  @Override
  public Scope untyped() {
    return this;
  }

  static Scope createGlobalScope(Node rootNode) {
    return new Scope.Simple(rootNode);
  }

  static Scope createChildScope(Scope parent, Node rootNode) {
    return new Scope.Simple(parent, rootNode);
  }

  /**
   * Declares a variable.
   *
   * @param name name of the variable
   * @param nameNode the NAME node declaring the variable
   * @param input the input in which this variable is defined.
   */
  // Non-final for PersisteneScope.
  Var declare(String name, Node nameNode, CompilerInput input) {
    checkArgument(!name.isEmpty());
    // Make sure that it's declared only once
    checkState(getOwnSlot(name) == null);
    Var var = new Var(name, nameNode, this, getVarCount(), input);
    declareInternal(name, var);
    return var;
  }

  @Override
  Var makeImplicitVar(ImplicitVar var) {
    return new Var(var.name, null /* nameNode */, this, -1 /* index */, null /* input */);
  }

  private static final class Simple extends Scope {
    final Scope parent;
    final int depth;

    Simple(Scope parent, Node rootNode) {
      super(rootNode);
      checkChildScope(parent);
      this.parent = parent;
      this.depth = parent.getDepth() + 1;
    }

    Simple(Node rootNode) {
      super(rootNode);
      checkRootScope();
      this.parent = null;
      this.depth = 0;
    }

    @Override
    public int getDepth() {
      return depth;
    }

    @Override
    public Scope getParent() {
      return parent;
    }
  }
}