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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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package jdk.nashorn.internal.lookup;

import static jdk.nashorn.internal.runtime.ECMAErrors.typeError;
import static jdk.nashorn.internal.runtime.ScriptRuntime.UNDEFINED;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import jdk.nashorn.internal.runtime.JSType;
import jdk.nashorn.internal.runtime.ScriptRuntime;

MethodHandle Lookup management for Nashorn.
/**
 * MethodHandle Lookup management for Nashorn.
 */
public final class Lookup {

    
A global singleton that points to the MethodHandleFunctionality. This is basically a collection of wrappers to the standard methods in MethodHandle, MethodHandles and Lookup, but instrumentation and debugging purposes we need intercept points. 
 All method handle operations in Nashorn should go through this field, not directly to the classes in java.lang.invoke /**
     * A global singleton that points to the {@link MethodHandleFunctionality}. This is basically
     * a collection of wrappers to the standard methods in {@link MethodHandle}, {@link MethodHandles} and
     * {@link java.lang.invoke.MethodHandles.Lookup}, but instrumentation and debugging purposes we need
     * intercept points.
     * <p>
     * All method handle operations in Nashorn should go through this field, not directly to the classes
     * in {@code java.lang.invoke}
     */
    public static final MethodHandleFunctionality MH = MethodHandleFactory.getFunctionality();

    
Method handle to the empty getter /** Method handle to the empty getter */
    public static final MethodHandle EMPTY_GETTER = findOwnMH("emptyGetter", Object.class, Object.class);

    
Method handle to the empty setter /** Method handle to the empty setter */
    public static final MethodHandle EMPTY_SETTER = findOwnMH("emptySetter", void.class, Object.class, Object.class);

    
Method handle to a getter or setter that only throws type error /** Method handle to a getter or setter that only throws type error */
    public static final MethodHandle TYPE_ERROR_THROWER = findOwnMH("typeErrorThrower", Object.class, Object.class);

    
Method handle to the most generic of getters, the one that returns an Object /** Method handle to the most generic of getters, the one that returns an Object */
    public static final MethodType GET_OBJECT_TYPE = MH.type(Object.class, Object.class);

    
Method handle to the most generic of setters, the one that takes an Object /** Method handle to the most generic of setters, the one that takes an Object */
    public static final MethodType SET_OBJECT_TYPE = MH.type(void.class, Object.class, Object.class);

    
Method handle to the primitive getters, the one that returns an long/int/double /** Method handle to the primitive getters, the one that returns an long/int/double */
    public static final MethodType GET_PRIMITIVE_TYPE = MH.type(long.class, Object.class);

    
Method handle to the primitive getters, the one that returns an long/int/double /** Method handle to the primitive getters, the one that returns an long/int/double */
    public static final MethodType SET_PRIMITIVE_TYPE = MH.type(void.class, Object.class, long.class);

    private Lookup() {
    }

    
Empty getter implementation. Nop
Params:
self – self reference
Returns:
undefined/**
     * Empty getter implementation. Nop
     * @param self self reference
     * @return undefined
     */
    public static Object emptyGetter(final Object self) {
        return UNDEFINED;
    }

    
Empty setter implementation. Nop
Params:
self –  self reference
value – value (ignored)/**
     * Empty setter implementation. Nop
     * @param self  self reference
     * @param value value (ignored)
     */
    public static void emptySetter(final Object self, final Object value) {
        // do nothing!!
    }

    
Return a method handle to the empty getter, with a different
return type value. It will still be undefined cast to whatever
return value property was specified
Params:
type – return value type
Returns:
undefined as return value type/**
     * Return a method handle to the empty getter, with a different
     * return type value. It will still be undefined cast to whatever
     * return value property was specified
     *
     * @param type return value type
     *
     * @return undefined as return value type
     */
    public static MethodHandle emptyGetter(final Class<?> type) {
        return filterReturnType(EMPTY_GETTER, type);
    }

    
Getter function that always throws type error
Params:
self –  self reference
Returns:
undefined (but throws error before return point)/**
     * Getter function that always throws type error
     *
     * @param self  self reference
     * @return undefined (but throws error before return point)
     */
    public static Object typeErrorThrower(final Object self) {
        throw typeError("strict.getter.setter.poison", ScriptRuntime.safeToString(self));
    }

    
This method filters primitive argument types using JavaScript semantics. For example,
an (int) cast of a double in Java land is not the same thing as invoking toInt32 on it.
If you are returning values to JavaScript that have to be of a specific type, this is
the correct return value filter to use, as the explicitCastArguments just uses the
Java boxing equivalents
Params:
mh –   method handle for which to filter argument value
n –    argument index
from – old argument type, the new one is given by the sent method handle
Returns:
method handle for appropriate argument type conversion/**
     * This method filters primitive argument types using JavaScript semantics. For example,
     * an (int) cast of a double in Java land is not the same thing as invoking toInt32 on it.
     * If you are returning values to JavaScript that have to be of a specific type, this is
     * the correct return value filter to use, as the explicitCastArguments just uses the
     * Java boxing equivalents
     *
     * @param mh   method handle for which to filter argument value
     * @param n    argument index
     * @param from old argument type, the new one is given by the sent method handle
     * @return method handle for appropriate argument type conversion
     */
    public static MethodHandle filterArgumentType(final MethodHandle mh, final int n, final Class<?> from) {
        final Class<?> to = mh.type().parameterType(n);

        if (from == int.class) {
            //fallthru
        } else if (from == long.class) {
            if (to == int.class) {
                return MH.filterArguments(mh, n, JSType.TO_INT32_L.methodHandle());
            }
            //fallthru
        } else if (from == double.class) {
            if (to == int.class) {
                return MH.filterArguments(mh, n, JSType.TO_INT32_D.methodHandle());
            } else if (to == long.class) {
                return MH.filterArguments(mh, n, JSType.TO_UINT32_D.methodHandle());
            }
            //fallthru
        } else if (!from.isPrimitive()) {
            if (to == int.class) {
                return MH.filterArguments(mh, n, JSType.TO_INT32.methodHandle());
            } else if (to == long.class) {
                return MH.filterArguments(mh, n, JSType.TO_UINT32.methodHandle());
            } else if (to == double.class) {
                return MH.filterArguments(mh, n, JSType.TO_NUMBER.methodHandle());
            } else if (!to.isPrimitive()) {
                return mh;
            }

            assert false : "unsupported Lookup.filterReturnType type " + from + " -> " + to;
        }

        //use a standard cast - we don't need to check JavaScript special cases
        return MH.explicitCastArguments(mh, mh.type().changeParameterType(n, from));
    }

    
This method filters primitive return types using JavaScript semantics. For example,
an (int) cast of a double in Java land is not the same thing as invoking toInt32 on it.
If you are returning values to JavaScript that have to be of a specific type, this is
the correct return value filter to use, as the explicitCastArguments just uses the
Java boxing equivalents
Params:
mh –   method handle for which to filter return value
type – new return type
Returns:
method handle for appropriate return type conversion/**
     * This method filters primitive return types using JavaScript semantics. For example,
     * an (int) cast of a double in Java land is not the same thing as invoking toInt32 on it.
     * If you are returning values to JavaScript that have to be of a specific type, this is
     * the correct return value filter to use, as the explicitCastArguments just uses the
     * Java boxing equivalents
     *
     * @param mh   method handle for which to filter return value
     * @param type new return type
     * @return method handle for appropriate return type conversion
     */
    public static MethodHandle filterReturnType(final MethodHandle mh, final Class<?> type) {
        final Class<?> retType = mh.type().returnType();

        if (retType == int.class) {
            //fallthru
        } else if (retType == long.class) {
            if (type == int.class) {
                return MH.filterReturnValue(mh, JSType.TO_INT32_L.methodHandle());
            }
            //fallthru
        } else if (retType == double.class) {
            if (type == int.class) {
                return MH.filterReturnValue(mh, JSType.TO_INT32_D.methodHandle());
            } else if (type == long.class) {
                return MH.filterReturnValue(mh, JSType.TO_UINT32_D.methodHandle());
            }
            //fallthru
        } else if (!retType.isPrimitive()) {
            if (type == int.class) {
                return MH.filterReturnValue(mh, JSType.TO_INT32.methodHandle());
            } else if (type == long.class) {
                return MH.filterReturnValue(mh, JSType.TO_UINT32.methodHandle());
            } else if (type == double.class) {
                return MH.filterReturnValue(mh, JSType.TO_NUMBER.methodHandle());
            } else if (!type.isPrimitive()) {
                return mh;
            }

            assert false : "unsupported Lookup.filterReturnType type " + retType + " -> " + type;
        }

        //use a standard cast - we don't need to check JavaScript special cases
        return MH.explicitCastArguments(mh, mh.type().changeReturnType(type));
    }

    private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
        return MH.findStatic(MethodHandles.lookup(), Lookup.class, name, MH.type(rtype, types));
    }

}