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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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/*
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Bob Jervis
 *   Google Inc.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package com.google.javascript.rhino.jstype;

import com.google.javascript.rhino.ErrorReporter;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;

/**
 * The bottom Object type, representing the subclass of all objects.
 *
 * Although JavaScript programmers can't explicitly denote the bottom Object type, it comes up in
 * static analysis. For example, if we have: 
 * var x = function() {};
 * if (x instanceof Array) {
 *   f(x);
 * }
 *  We need to be able to assign {@code x} a type within the {@code f(x)} call. It has no
 * possible type, but {@code x} would not be legal if f expected a string. So we assign it the
 * {@code NoObjectType}.
 *
 * @see Bottom types
 */
public class NoObjectType extends FunctionType {
  private static final long serialVersionUID = 1L;

  NoObjectType(JSTypeRegistry registry) {
    super(
        FunctionType.builder(registry)
            .withKind(FunctionType.Kind.NONE)
            .withReturnsOwnInstanceType()
            .forNativeType());
    this.eagerlyResolveToSelf();
  }

  @Override
  JSTypeClass getTypeClass() {
    return JSTypeClass.NO_OBJECT;
  }

  @Override
  public final FunctionType toMaybeFunctionType() {
    return null;
  }

  @Override
  public boolean isNoObjectType() {
    return true;
  }

  @Override
  public final ObjectType getImplicitPrototype() {
    return null;
  }

  @Override
  public String getReferenceName() {
    return null;
  }
  @Override
  public final boolean matchesNumberContext() {
    return true;
  }

  @Override
  public final boolean matchesObjectContext() {
    return true;
  }

  @Override
  public final boolean matchesStringContext() {
    return true;
  }

  @Override
  public final boolean matchesSymbolContext() {
    return true;
  }

  @Override
  int recursionUnsafeHashCode() {
    return System.identityHashCode(this);
  }

  @Override
  final boolean defineProperty(String propertyName, JSType type,
      boolean inferred, Node propertyNode) {
    // nothing, all properties are defined
    return true;
  }

  @Override
  public final boolean removeProperty(String name) {
    return false;
  }

  @Override
  public final void setPropertyJSDocInfo(String propertyName, JSDocInfo info) {
    // Do nothing, specific properties do not have JSDocInfo.
  }

  @Override
  public  T visit(Visitor visitor) {
    return visitor.caseNoObjectType();
  }

  @Override  T visit(RelationshipVisitor visitor, JSType that) {
    return visitor.caseNoObjectType(that);
  }

  @Override
  void appendTo(TypeStringBuilder sb) {
    sb.append(sb.isForAnnotations() ? "?" : "NoObject");
  }

  @Override
  public final FunctionType getConstructor() {
    return null;
  }

  @Override
  final JSType resolveInternal(ErrorReporter reporter) {
    throw new AssertionError();
  }
}