1 /*
   2  * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.nashorn.internal.runtime;
  27 
  28 import static jdk.nashorn.internal.lookup.Lookup.MH;
  29 import static jdk.nashorn.internal.runtime.ECMAErrors.typeError;
  30 
  31 import java.lang.invoke.MethodHandle;
  32 import java.lang.invoke.MethodHandles;
  33 import jdk.internal.dynalink.CallSiteDescriptor;
  34 import jdk.internal.dynalink.linker.GuardedInvocation;
  35 import jdk.internal.dynalink.support.CallSiteDescriptorFactory;
  36 import jdk.internal.dynalink.support.Guards;
  37 import jdk.nashorn.internal.runtime.linker.NashornCallSiteDescriptor;
  38 
  39 /**
  40  * Unique instance of this class is used to represent JavaScript undefined.
  41  */
  42 public final class Undefined extends DefaultPropertyAccess {
  43 
  44     private Undefined() {
  45     }
  46 
  47     private static final Undefined UNDEFINED = new Undefined();
  48     private static final Undefined EMPTY     = new Undefined();
  49 
  50     // Guard used for indexed property access/set on the Undefined instance
  51     private static final MethodHandle UNDEFINED_GUARD = Guards.getIdentityGuard(UNDEFINED);
  52 
  53     /**
  54      * Get the value of {@code undefined}, this is represented as a global singleton
  55      * instance of this class. It can always be reference compared
  56      *
  57      * @return the undefined object
  58      */
  59     public static Undefined getUndefined() {
  60         return UNDEFINED;
  61     }
  62 
  63     /**
  64      * Get the value of {@code empty}. This is represented as a global singleton
  65      * instanceof this class. It can always be reference compared.
  66      * <p>
  67      * We need empty to differentiate behavior in things like array iterators
  68      * <p>
  69      * @return the empty object
  70      */
  71     public static Undefined getEmpty() {
  72         return EMPTY;
  73     }
  74 
  75     /**
  76      * Get the class name of Undefined
  77      * @return "Undefined"
  78      */
  79     @SuppressWarnings("static-method")
  80     public String getClassName() {
  81         return "Undefined";
  82     }
  83 
  84     @Override
  85     public String toString() {
  86         return "undefined";
  87     }
  88 
  89     /**
  90      * Lookup the appropriate method for an invoke dynamic call.
  91      * @param desc The invoke dynamic callsite descriptor.
  92      * @return GuardedInvocation to be invoked at call site.
  93      */
  94     public static GuardedInvocation lookup(final CallSiteDescriptor desc) {
  95         final String operator = CallSiteDescriptorFactory.tokenizeOperators(desc).get(0);
  96 
  97         switch (operator) {
  98         case "new":
  99         case "call": {
 100             final String name = NashornCallSiteDescriptor.getFunctionDescription(desc);
 101             final String msg = name != null? "not.a.function" : "cant.call.undefined";
 102             throw typeError(msg, name);
 103         }
 104 
 105         case "callMethod":
 106             throw lookupTypeError("cant.read.property.of.undefined", desc);
 107         // NOTE: we support getElem and setItem as JavaScript doesn't distinguish items from properties. Nashorn itself
 108         // emits "dyn:getProp:identifier" for "<expr>.<identifier>" and "dyn:getElem" for "<expr>[<expr>]", but we are
 109         // more flexible here and dispatch not on operation name (getProp vs. getElem), but rather on whether the
 110         // operation has an associated name or not.
 111         case "getProp":
 112         case "getElem":
 113         case "getMethod":
 114             if (desc.getNameTokenCount() < 3) {
 115                 return findGetIndexMethod(desc);
 116             }
 117             return findGetMethod(desc);
 118         case "setProp":
 119         case "setElem":
 120             if (desc.getNameTokenCount() < 3) {
 121                 return findSetIndexMethod(desc);
 122             }
 123             return findSetMethod(desc);
 124         default:
 125             break;
 126         }
 127 
 128         return null;
 129     }
 130 
 131     private static ECMAException lookupTypeError(final String msg, final CallSiteDescriptor desc) {
 132         final String name = desc.getNameToken(2);
 133         return typeError(msg, name != null && !name.isEmpty()? name : null);
 134     }
 135 
 136     private static final MethodHandle GET_METHOD = findOwnMH("get", Object.class, Object.class);
 137     private static final MethodHandle SET_METHOD = MH.insertArguments(findOwnMH("set", void.class, Object.class, Object.class, int.class), 3, NashornCallSiteDescriptor.CALLSITE_STRICT);
 138 
 139     private static GuardedInvocation findGetMethod(final CallSiteDescriptor desc) {
 140         return new GuardedInvocation(MH.insertArguments(GET_METHOD, 1, desc.getNameToken(2)), UNDEFINED_GUARD).asType(desc);
 141     }
 142 
 143     private static GuardedInvocation findGetIndexMethod(final CallSiteDescriptor desc) {
 144         return new GuardedInvocation(GET_METHOD, UNDEFINED_GUARD).asType(desc);
 145     }
 146 
 147     private static GuardedInvocation findSetMethod(final CallSiteDescriptor desc) {
 148         return new GuardedInvocation(MH.insertArguments(SET_METHOD, 1, desc.getNameToken(2)), UNDEFINED_GUARD).asType(desc);
 149     }
 150 
 151     private static GuardedInvocation findSetIndexMethod(final CallSiteDescriptor desc) {
 152         return new GuardedInvocation(SET_METHOD, UNDEFINED_GUARD).asType(desc);
 153     }
 154 
 155     @Override
 156     public Object get(final Object key) {
 157         throw typeError("cant.read.property.of.undefined", ScriptRuntime.safeToString(key));
 158     }
 159 
 160     @Override
 161     public void set(final Object key, final Object value, final int flags) {
 162         throw typeError("cant.set.property.of.undefined", ScriptRuntime.safeToString(key));
 163     }
 164 
 165     @Override
 166     public boolean delete(final Object key, final boolean strict) {
 167         throw typeError("cant.delete.property.of.undefined", ScriptRuntime.safeToString(key));
 168     }
 169 
 170     @Override
 171     public boolean has(final Object key) {
 172         return false;
 173     }
 174 
 175     @Override
 176     public boolean hasOwnProperty(final Object key) {
 177         return false;
 178     }
 179 
 180     private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
 181         return MH.findVirtual(MethodHandles.lookup(), Undefined.class, name, MH.type(rtype, types));
 182     }
 183 }
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