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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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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):
 *   John Lenz
 *   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;

/**
 * A "can cast to" relationship visitor.
 */
class CanCastToVisitor implements RelationshipVisitor {

  @Override
  public Boolean caseUnknownType(JSType thisType, JSType thatType) {
    return true;
  }

  @Override
  public Boolean caseNoType(JSType thatType) {
    return true;
  }

  @Override
  public Boolean caseNoObjectType(JSType thatType) {
    return true; // TODO(johnlenz): restrict to objects
  }

  @Override
  public Boolean caseAllType(JSType thatType) {
    return true;
  }

  boolean canCastToUnion(JSType thisType, UnionType unionType) {
    for (JSType type : unionType.getAlternates()) {
      if (thisType.visit(this, type)) {
        return true;
      }
    }
    return false;
  }

  boolean canCastToFunction(JSType thisType, FunctionType functionType) {
    if (thisType.isFunctionType()) {
      // TODO(johnlenz): visit function parts
      return true;
    } else {
      return thisType.isSubtypeOf(functionType)
          || functionType.isSubtype(thisType);
    }
  }

  private boolean isInterface(JSType type) {
    ObjectType objType = type.toObjectType();
    if (objType != null) {
      JSType constructor = objType.getConstructor();
      return constructor != null && constructor.isInterface();
    }
    return false;
  }

  Boolean castCastToHelper(JSType thisType, JSType thatType) {
    if (thatType.isUnknownType()
        || thatType.isAllType()
        || thatType.isNoObjectType() // TODO(johnlenz): restrict to objects
        || thatType.isNoType()) {
      return true;
    } else if (thisType.isRecordType() || thatType.isRecordType()) {
      return true;  // TODO(johnlenz): are there any misuses we can catch?
    } else if (isInterface(thisType) || isInterface(thatType)) {
      return true;  // TODO(johnlenz): are there any misuses we can catch?
    } else if (thatType.isEnumElementType()) {
      return thisType.visit(this,
          thatType.toMaybeEnumElementType().getPrimitiveType());
    } else if (thatType.isUnionType()) {
      return canCastToUnion(thisType, thatType.toMaybeUnionType());
    } else if (thatType.isFunctionType()) {
      return canCastToFunction(thisType, thatType.toMaybeFunctionType());
    } else if (thatType.isTemplatizedType()) {
      // TODO(johnlenz): once the templated type work is finished,
      // restrict the type parameters.
      return thisType.visit(this,
          thatType.toMaybeTemplatizedType().getReferencedTypeInternal());
    }

    return thisType.isSubtypeOf(thatType) || thatType.isSubtypeOf(thisType);
  }

  @Override
  public Boolean caseValueType(ValueType thisType, JSType thatType) {
    return castCastToHelper(thisType, thatType);
  }

  @Override
  public Boolean caseObjectType(ObjectType thisType, JSType thatType) {
    return castCastToHelper(thisType, thatType);
  }

  @Override
  public Boolean caseFunctionType(FunctionType thisType, JSType thatType) {
    return castCastToHelper(thisType, thatType);
  }

  @Override
  public Boolean caseUnionType(UnionType thisType, JSType thatType) {
    boolean visited = false;
    for (JSType type : thisType.getAlternates()) {
      if (type.isVoidType() || type.isNullType()) {
        // Don't allow if the only match between the types is null or void,
        // otherwise any nullable type would be castable to any other nullable
        // type and we don't want that.
      } else {
        visited = true;
        if (type.visit(this, thatType)) {
          return true;
        }
      }
    }

    // Special case the "null|undefined" union and allow it to be cast
    // to any cast to any type containing allowing either null|undefined.
    if (!visited) {
      JSType NULL_TYPE = thisType.getNativeType(JSTypeNative.NULL_TYPE);
      JSType VOID_TYPE = thisType.getNativeType(JSTypeNative.VOID_TYPE);
      return NULL_TYPE.visit(this, thatType) || VOID_TYPE.visit(this, thatType);
    }

    return false;
  }

  @Override
  public Boolean caseTemplatizedType(
      TemplatizedType thisType, JSType thatType) {
    // TODO(johnlenz): once the templated type work is finished,
    // restrict the type parameters.
    return thisType.getReferencedTypeInternal().visit(this, thatType);
  }

  @Override
  public Boolean caseTemplateType(TemplateType thisType, JSType thatType) {
    return true;
  }

  @Override
  public Boolean caseEnumElementType(
      EnumElementType typeType, JSType thatType) {
    return typeType.getPrimitiveType().visit(this, thatType);
  }
}