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.dynalink.CallSiteDescriptor;
  34 import jdk.dynalink.NamedOperation;
  35 import jdk.dynalink.linker.GuardedInvocation;
  36 import jdk.dynalink.linker.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         switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
  96         case CALL:
  97         case NEW:
  98             final String name = NashornCallSiteDescriptor.getOperand(desc);
  99             final String msg = name != null? "not.a.function" : "cant.call.undefined";
 100             throw typeError(msg, name);
 101         case GET:
 102             // NOTE: we support GET:ELEMENT and SET:ELEMENT as JavaScript doesn't distinguish items from properties. Nashorn itself
 103             // emits "GET:PROPERTY|ELEMENT|METHOD:identifier" for "<expr>.<identifier>" and "GET:ELEMENT|PROPERTY|METHOD" for "<expr>[<expr>]", but we are
 104             // more flexible here and dispatch not on operation name (getProp vs. getElem), but rather on whether the
 105             // operation has an associated name or not.
 106             if (!(desc.getOperation() instanceof NamedOperation)) {
 107                 return findGetIndexMethod(desc);
 108             }
 109             return findGetMethod(desc);
 110         case SET:
 111             if (!(desc.getOperation() instanceof NamedOperation)) {
 112                 return findSetIndexMethod(desc);
 113             }
 114             return findSetMethod(desc);
 115         case REMOVE:
 116             if (!(desc.getOperation() instanceof NamedOperation)) {
 117                 return findDeleteIndexMethod(desc);
 118             }
 119             return findDeleteMethod(desc);
 120         default:
 121         }
 122         return null;
 123     }
 124 
 125     private static ECMAException lookupTypeError(final String msg, final CallSiteDescriptor desc) {
 126         final String name = NashornCallSiteDescriptor.getOperand(desc);
 127         return typeError(msg, name != null && !name.isEmpty()? name : null);
 128     }
 129 
 130     private static final MethodHandle GET_METHOD = findOwnMH("get", Object.class, Object.class);
 131     private static final MethodHandle SET_METHOD = MH.insertArguments(findOwnMH("set", void.class, Object.class, Object.class, int.class), 3, NashornCallSiteDescriptor.CALLSITE_STRICT);
 132     private static final MethodHandle DELETE_METHOD = MH.insertArguments(findOwnMH("delete", boolean.class, Object.class, boolean.class), 2, false);
 133 
 134     private static GuardedInvocation findGetMethod(final CallSiteDescriptor desc) {
 135         return new GuardedInvocation(MH.insertArguments(GET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
 136     }
 137 
 138     private static GuardedInvocation findGetIndexMethod(final CallSiteDescriptor desc) {
 139         return new GuardedInvocation(GET_METHOD, UNDEFINED_GUARD).asType(desc);
 140     }
 141 
 142     private static GuardedInvocation findSetMethod(final CallSiteDescriptor desc) {
 143         return new GuardedInvocation(MH.insertArguments(SET_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
 144     }
 145 
 146     private static GuardedInvocation findSetIndexMethod(final CallSiteDescriptor desc) {
 147         return new GuardedInvocation(SET_METHOD, UNDEFINED_GUARD).asType(desc);
 148     }
 149 
 150     private static GuardedInvocation findDeleteMethod(final CallSiteDescriptor desc) {
 151         return new GuardedInvocation(MH.insertArguments(DELETE_METHOD, 1, NashornCallSiteDescriptor.getOperand(desc)), UNDEFINED_GUARD).asType(desc);
 152     }
 153 
 154     private static GuardedInvocation findDeleteIndexMethod(final CallSiteDescriptor desc) {
 155         return new GuardedInvocation(DELETE_METHOD, UNDEFINED_GUARD).asType(desc);
 156     }
 157 
 158 
 159     @Override
 160     public Object get(final Object key) {
 161         throw typeError("cant.read.property.of.undefined", ScriptRuntime.safeToString(key));
 162     }
 163 
 164     @Override
 165     public void set(final Object key, final Object value, final int flags) {
 166         throw typeError("cant.set.property.of.undefined", ScriptRuntime.safeToString(key));
 167     }
 168 
 169     @Override
 170     public boolean delete(final Object key, final boolean strict) {
 171         throw typeError("cant.delete.property.of.undefined", ScriptRuntime.safeToString(key));
 172     }
 173 
 174     @Override
 175     public boolean has(final Object key) {
 176         return false;
 177     }
 178 
 179     @Override
 180     public boolean hasOwnProperty(final Object key) {
 181         return false;
 182     }
 183 
 184     private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
 185         return MH.findVirtual(MethodHandles.lookup(), Undefined.class, name, MH.type(rtype, types));
 186     }
 187 }