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Byte Buddy is a Java library for creating Java classes at run time. This artifact is a build of Byte Buddy with a remaining dependency onto ASM. You should never depend on this module without repackaging Byte Buddy and ASM into your own namespace.
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/*
 * Copyright 2014 - Present Rafael Winterhalter
 *
 * Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.bytebuddy.implementation.bind.annotation;

import net.bytebuddy.description.annotation.AnnotationDescription;
import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.description.method.ParameterDescription;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.implementation.Implementation;
import net.bytebuddy.implementation.bind.MethodDelegationBinder;
import net.bytebuddy.implementation.bytecode.StackManipulation;
import net.bytebuddy.implementation.bytecode.assign.Assigner;
import net.bytebuddy.implementation.bytecode.constant.NullConstant;
import net.bytebuddy.implementation.bytecode.member.MethodVariableAccess;

import java.lang.annotation.*;

import static net.bytebuddy.matcher.ElementMatchers.named;

/**
 * 
 * Parameters that are annotated with this annotation will be assigned a reference to the instrumented object, if
 * the instrumented method is not static. Otherwise, the method with this parameter annotation will be excluded from
 * the list of possible binding candidates of the static source method.
 * 
 * 
 * Important: Don't confuse this annotation with {@link net.bytebuddy.asm.Advice.This} or
 * {@link net.bytebuddy.asm.MemberSubstitution.This}. This annotation should be used with
 * {@link net.bytebuddy.implementation.MethodDelegation} only.
 * 
 *
 * @see net.bytebuddy.implementation.MethodDelegation
 * @see net.bytebuddy.implementation.bind.annotation.TargetMethodAnnotationDrivenBinder
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
public @interface This {

    /**
     * Determines if the annotated parameter should be bound to {@code null} when intercepting a {@code static} method.
     *
     * @return {@code true} if the annotated parameter should be bound to {@code null} as a fallback.
     */
    boolean optional() default false;

    /**
     * A binder for handling the
     * {@link net.bytebuddy.implementation.bind.annotation.This}
     * annotation.
     *
     * @see TargetMethodAnnotationDrivenBinder
     */
    enum Binder implements TargetMethodAnnotationDrivenBinder.ParameterBinder {

        /**
         * The singleton instance.
         */
        INSTANCE;

        /**
         * A description of the {@link Pipe#serializableProxy()} method.
         */
        private static final MethodDescription.InDefinedShape OPTIONAL = TypeDescription.ForLoadedType.of(This.class)
                .getDeclaredMethods()
                .filter(named("optional"))
                .getOnly();

        /**
         * {@inheritDoc}
         */
        public Class getHandledType() {
            return This.class;
        }

        /**
         * {@inheritDoc}
         */
        public MethodDelegationBinder.ParameterBinding bind(AnnotationDescription.Loadable annotation,
                                                               MethodDescription source,
                                                               ParameterDescription target,
                                                               Implementation.Target implementationTarget,
                                                               Assigner assigner,
                                                               Assigner.Typing typing) {
            if (target.getType().isPrimitive()) {
                throw new IllegalStateException(target + " uses a primitive type with a @This annotation");
            } else if (target.getType().isArray()) {
                throw new IllegalStateException(target + " uses an array type with a @This annotation");
            } else if (source.isStatic() && !annotation.getValue(OPTIONAL).resolve(Boolean.class)) {
                return MethodDelegationBinder.ParameterBinding.Illegal.INSTANCE;
            }
            return new MethodDelegationBinder.ParameterBinding.Anonymous(source.isStatic()
                    ? NullConstant.INSTANCE
                    : new StackManipulation.Compound(MethodVariableAccess.loadThis(),
                    assigner.assign(implementationTarget.getInstrumentedType().asGenericType(), target.getType(), typing)));
        }
    }
}