/*

 * Copyright (c) 2008, 2016, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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 *

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package java.lang.invoke;

import java.lang.reflect.*;

import java.util.*;

import sun.invoke.util.ValueConversions;

import sun.invoke.util.VerifyAccess;

import sun.invoke.util.Wrapper;

import sun.reflect.CallerSensitive;

import sun.reflect.Reflection;

import sun.reflect.misc.ReflectUtil;

import sun.security.util.SecurityConstants;

import java.lang.invoke.LambdaForm.BasicType;

import static java.lang.invoke.MethodHandleStatics.*;

import static java.lang.invoke.MethodHandleImpl.Intrinsic;

import static java.lang.invoke.MethodHandleNatives.Constants.*;

import java.util.concurrent.ConcurrentHashMap;

import java.util.stream.Collectors;

import java.util.stream.Stream;

/**

 * This class consists exclusively of static methods that operate on or return

 * method handles. They fall into several categories:

 * <ul>

 * <li>Lookup methods which help create method handles for methods and fields.

 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.

 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.

 * </ul>

 *

 * @author John Rose, JSR 292 EG

 * @since 1.7

 */

public class MethodHandles {

    private MethodHandles() { }  // do not instantiate

    private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();

    // See IMPL_LOOKUP below.

    //// Method handle creation from ordinary methods.

    /**

     * Returns a {@link Lookup lookup object} with

     * full capabilities to emulate all supported bytecode behaviors of the caller.

     * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.

     * Factory methods on the lookup object can create

     * <a href="MethodHandleInfo.html#directmh">direct method handles</a>

     * for any member that the caller has access to via bytecodes,

     * including protected and private fields and methods.

     * This lookup object is a <em>capability</em> which may be delegated to trusted agents.

     * Do not store it in place where untrusted code can access it.

     * <p>

     * This method is caller sensitive, which means that it may return different

     * values to different callers.

     * <p>

     * For any given caller class {@code C}, the lookup object returned by this call

     * has equivalent capabilities to any lookup object

     * supplied by the JVM to the bootstrap method of an

     * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>

     * executing in the same caller class {@code C}.

     * @return a lookup object for the caller of this method, with private access

     */

    @CallerSensitive

    public static Lookup lookup() {

        return new Lookup(Reflection.getCallerClass());

    }

    /**

     * Returns a {@link Lookup lookup object} which is trusted minimally.

     * It can only be used to create method handles to

     * publicly accessible fields and methods.

     * <p>

     * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}

     * of this lookup object will be {@link java.lang.Object}.

     *

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * The lookup class can be changed to any other class {@code C} using an expression of the form

     * {@link Lookup#in publicLookup().in(C.class)}.

     * Since all classes have equal access to public names,

     * such a change would confer no new access rights.

     * A public lookup object is always subject to

     * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.

     * Also, it cannot access

     * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.

     * @return a lookup object which is trusted minimally

     */

    public static Lookup publicLookup() {

        return Lookup.PUBLIC_LOOKUP;

    }

    /**

     * Performs an unchecked "crack" of a

     * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.

     * The result is as if the user had obtained a lookup object capable enough

     * to crack the target method handle, called

     * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}

     * on the target to obtain its symbolic reference, and then called

     * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}

     * to resolve the symbolic reference to a member.

     * <p>

     * If there is a security manager, its {@code checkPermission} method

     * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.

     * @param <T> the desired type of the result, either {@link Member} or a subtype

     * @param target a direct method handle to crack into symbolic reference components

     * @param expected a class object representing the desired result type {@code T}

     * @return a reference to the method, constructor, or field object

     * @exception SecurityException if the caller is not privileged to call {@code setAccessible}

     * @exception NullPointerException if either argument is {@code null}

     * @exception IllegalArgumentException if the target is not a direct method handle

     * @exception ClassCastException if the member is not of the expected type

     * @since 1.8

     */

    public static <T extends Member> T

    reflectAs(Class<T> expected, MethodHandle target) {

        SecurityManager smgr = System.getSecurityManager();

        if (smgr != null)  smgr.checkPermission(ACCESS_PERMISSION);

        Lookup lookup = Lookup.IMPL_LOOKUP;  // use maximally privileged lookup

        return lookup.revealDirect(target).reflectAs(expected, lookup);

    }

    // Copied from AccessibleObject, as used by Method.setAccessible, etc.:

    private static final java.security.Permission ACCESS_PERMISSION =

        new ReflectPermission("suppressAccessChecks");

    /**

     * A <em>lookup object</em> is a factory for creating method handles,

     * when the creation requires access checking.

     * Method handles do not perform

     * access checks when they are called, but rather when they are created.

     * Therefore, method handle access

     * restrictions must be enforced when a method handle is created.

     * The caller class against which those restrictions are enforced

     * is known as the {@linkplain #lookupClass lookup class}.

     * <p>

     * A lookup class which needs to create method handles will call

     * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.

     * When the {@code Lookup} factory object is created, the identity of the lookup class is

     * determined, and securely stored in the {@code Lookup} object.

     * The lookup class (or its delegates) may then use factory methods

     * on the {@code Lookup} object to create method handles for access-checked members.

     * This includes all methods, constructors, and fields which are allowed to the lookup class,

     * even private ones.

     *

     * <h1><a name="lookups"></a>Lookup Factory Methods</h1>

     * The factory methods on a {@code Lookup} object correspond to all major

     * use cases for methods, constructors, and fields.

     * Each method handle created by a factory method is the functional

     * equivalent of a particular <em>bytecode behavior</em>.

     * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)

     * Here is a summary of the correspondence between these factory methods and

     * the behavior of the resulting method handles:

     * <table border=1 cellpadding=5 summary="lookup method behaviors">

     * <tr>

     *     <th><a name="equiv"></a>lookup expression</th>

     *     <th>member</th>

     *     <th>bytecode behavior</th>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>

     *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>

     *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>

     *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>

     *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>

     *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>

     *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>

     *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>

     *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>

     *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>

     *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>

     *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>

     *     <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>

     *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>

     * </tr>

     * <tr>

     *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>

     *     <td>{@code class C { ... }}</td><td>{@code C.class;}</td>

     * </tr>

     * </table>

     *

     * Here, the type {@code C} is the class or interface being searched for a member,

     * documented as a parameter named {@code refc} in the lookup methods.

     * The method type {@code MT} is composed from the return type {@code T}

     * and the sequence of argument types {@code A*}.

     * The constructor also has a sequence of argument types {@code A*} and

     * is deemed to return the newly-created object of type {@code C}.

     * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.

     * The formal parameter {@code this} stands for the self-reference of type {@code C};

     * if it is present, it is always the leading argument to the method handle invocation.

     * (In the case of some {@code protected} members, {@code this} may be

     * restricted in type to the lookup class; see below.)

     * The name {@code arg} stands for all the other method handle arguments.

     * In the code examples for the Core Reflection API, the name {@code thisOrNull}

     * stands for a null reference if the accessed method or field is static,

     * and {@code this} otherwise.

     * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand

     * for reflective objects corresponding to the given members.

     * <p>

     * The bytecode behavior for a {@code findClass} operation is a load of a constant class,

     * as if by {@code ldc CONSTANT_Class}.

     * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.

     * <p>

     * In cases where the given member is of variable arity (i.e., a method or constructor)

     * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.

     * In all other cases, the returned method handle will be of fixed arity.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * The equivalence between looked-up method handles and underlying

     * class members and bytecode behaviors

     * can break down in a few ways:

     * <ul style="font-size:smaller;">

     * <li>If {@code C} is not symbolically accessible from the lookup class's loader,

     * the lookup can still succeed, even when there is no equivalent

     * Java expression or bytecoded constant.

     * <li>Likewise, if {@code T} or {@code MT}

     * is not symbolically accessible from the lookup class's loader,

     * the lookup can still succeed.

     * For example, lookups for {@code MethodHandle.invokeExact} and

     * {@code MethodHandle.invoke} will always succeed, regardless of requested type.

     * <li>If there is a security manager installed, it can forbid the lookup

     * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).

     * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}

     * constant is not subject to security manager checks.

     * <li>If the looked-up method has a

     * <a href="MethodHandle.html#maxarity">very large arity</a>,

     * the method handle creation may fail, due to the method handle

     * type having too many parameters.

     * </ul>

     *

     * <h1><a name="access"></a>Access checking</h1>

     * Access checks are applied in the factory methods of {@code Lookup},

     * when a method handle is created.

     * This is a key difference from the Core Reflection API, since

     * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}

     * performs access checking against every caller, on every call.

     * <p>

     * All access checks start from a {@code Lookup} object, which

     * compares its recorded lookup class against all requests to

     * create method handles.

     * A single {@code Lookup} object can be used to create any number

     * of access-checked method handles, all checked against a single

     * lookup class.

     * <p>

     * A {@code Lookup} object can be shared with other trusted code,

     * such as a metaobject protocol.

     * A shared {@code Lookup} object delegates the capability

     * to create method handles on private members of the lookup class.

     * Even if privileged code uses the {@code Lookup} object,

     * the access checking is confined to the privileges of the

     * original lookup class.

     * <p>

     * A lookup can fail, because

     * the containing class is not accessible to the lookup class, or

     * because the desired class member is missing, or because the

     * desired class member is not accessible to the lookup class, or

     * because the lookup object is not trusted enough to access the member.

     * In any of these cases, a {@code ReflectiveOperationException} will be

     * thrown from the attempted lookup.  The exact class will be one of

     * the following:

     * <ul>

     * <li>NoSuchMethodException &mdash; if a method is requested but does not exist

     * <li>NoSuchFieldException &mdash; if a field is requested but does not exist

     * <li>IllegalAccessException &mdash; if the member exists but an access check fails

     * </ul>

     * <p>

     * In general, the conditions under which a method handle may be

     * looked up for a method {@code M} are no more restrictive than the conditions

     * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.

     * Where the JVM would raise exceptions like {@code NoSuchMethodError},

     * a method handle lookup will generally raise a corresponding

     * checked exception, such as {@code NoSuchMethodException}.

     * And the effect of invoking the method handle resulting from the lookup

     * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>

     * to executing the compiled, verified, and resolved call to {@code M}.

     * The same point is true of fields and constructors.

     * <p style="font-size:smaller;">

     * <em>Discussion:</em>

     * Access checks only apply to named and reflected methods,

     * constructors, and fields.

     * Other method handle creation methods, such as

     * {@link MethodHandle#asType MethodHandle.asType},

     * do not require any access checks, and are used

     * independently of any {@code Lookup} object.

     * <p>

     * If the desired member is {@code protected}, the usual JVM rules apply,

     * including the requirement that the lookup class must be either be in the

     * same package as the desired member, or must inherit that member.

     * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)

     * In addition, if the desired member is a non-static field or method

     * in a different package, the resulting method handle may only be applied

     * to objects of the lookup class or one of its subclasses.

     * This requirement is enforced by narrowing the type of the leading

     * {@code this} parameter from {@code C}

     * (which will necessarily be a superclass of the lookup class)

     * to the lookup class itself.

     * <p>

     * The JVM imposes a similar requirement on {@code invokespecial} instruction,

     * that the receiver argument must match both the resolved method <em>and</em>

     * the current class.  Again, this requirement is enforced by narrowing the

     * type of the leading parameter to the resulting method handle.

     * (See the Java Virtual Machine Specification, section 4.10.1.9.)

     * <p>

     * The JVM represents constructors and static initializer blocks as internal methods

     * with special names ({@code "<init>"} and {@code "<clinit>"}).

     * The internal syntax of invocation instructions allows them to refer to such internal

     * methods as if they were normal methods, but the JVM bytecode verifier rejects them.

     * A lookup of such an internal method will produce a {@code NoSuchMethodException}.

     * <p>

     * In some cases, access between nested classes is obtained by the Java compiler by creating

     * an wrapper method to access a private method of another class

     * in the same top-level declaration.

     * For example, a nested class {@code C.D}

     * can access private members within other related classes such as

     * {@code C}, {@code C.D.E}, or {@code C.B},

     * but the Java compiler may need to generate wrapper methods in

     * those related classes.  In such cases, a {@code Lookup} object on

     * {@code C.E} would be unable to those private members.

     * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,

     * which can transform a lookup on {@code C.E} into one on any of those other

     * classes, without special elevation of privilege.

     * <p>

     * The accesses permitted to a given lookup object may be limited,

     * according to its set of {@link #lookupModes lookupModes},

     * to a subset of members normally accessible to the lookup class.

     * For example, the {@link MethodHandles#publicLookup publicLookup}

     * method produces a lookup object which is only allowed to access

     * public members in public classes.

     * The caller sensitive method {@link MethodHandles#lookup lookup}

     * produces a lookup object with full capabilities relative to

     * its caller class, to emulate all supported bytecode behaviors.

     * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object

     * with fewer access modes than the original lookup object.

     *

     * <p style="font-size:smaller;">

     * <a name="privacc"></a>

     * <em>Discussion of private access:</em>

     * We say that a lookup has <em>private access</em>

     * if its {@linkplain #lookupModes lookup modes}

     * include the possibility of accessing {@code private} members.

     * As documented in the relevant methods elsewhere,

     * only lookups with private access possess the following capabilities:

     * <ul style="font-size:smaller;">

     * <li>access private fields, methods, and constructors of the lookup class

     * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,

     *     such as {@code Class.forName}

     * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions

     * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>

     *     for classes accessible to the lookup class

     * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes

     *     within the same package member

     * </ul>

     * <p style="font-size:smaller;">

     * Each of these permissions is a consequence of the fact that a lookup object

     * with private access can be securely traced back to an originating class,

     * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions

     * can be reliably determined and emulated by method handles.

     *

     * <h1><a name="secmgr"></a>Security manager interactions</h1>

     * Although bytecode instructions can only refer to classes in

     * a related class loader, this API can search for methods in any

     * class, as long as a reference to its {@code Class} object is

     * available.  Such cross-loader references are also possible with the

     * Core Reflection API, and are impossible to bytecode instructions

     * such as {@code invokestatic} or {@code getfield}.

     * There is a {@linkplain java.lang.SecurityManager security manager API}

     * to allow applications to check such cross-loader references.

     * These checks apply to both the {@code MethodHandles.Lookup} API

     * and the Core Reflection API

     * (as found on {@link java.lang.Class Class}).

     * <p>

     * If a security manager is present, member and class lookups are subject to

     * additional checks.

     * From one to three calls are made to the security manager.

     * Any of these calls can refuse access by throwing a

     * {@link java.lang.SecurityException SecurityException}.

     * Define {@code smgr} as the security manager,

     * {@code lookc} as the lookup class of the current lookup object,

     * {@code refc} as the containing class in which the member

     * is being sought, and {@code defc} as the class in which the

     * member is actually defined.

     * (If a class or other type is being accessed,

     * the {@code refc} and {@code defc} values are the class itself.)

     * The value {@code lookc} is defined as <em>not present</em>

     * if the current lookup object does not have

     * <a href="MethodHandles.Lookup.html#privacc">private access</a>.

     * The calls are made according to the following rules:

     * <ul>

     * <li><b>Step 1:</b>

     *     If {@code lookc} is not present, or if its class loader is not

     *     the same as or an ancestor of the class loader of {@code refc},

     *     then {@link SecurityManager#checkPackageAccess

     *     smgr.checkPackageAccess(refcPkg)} is called,

     *     where {@code refcPkg} is the package of {@code refc}.

     * <li><b>Step 2a:</b>

     *     If the retrieved member is not public and

     *     {@code lookc} is not present, then

     *     {@link SecurityManager#checkPermission smgr.checkPermission}

     *     with {@code RuntimePermission("accessDeclaredMembers")} is called.

     * <li><b>Step 2b:</b>

     *     If the retrieved class has a {@code null} class loader,

     *     and {@code lookc} is not present, then

     *     {@link SecurityManager#checkPermission smgr.checkPermission}

     *     with {@code RuntimePermission("getClassLoader")} is called.

     * <li><b>Step 3:</b>

     *     If the retrieved member is not public,

     *     and if {@code lookc} is not present,

     *     and if {@code defc} and {@code refc} are different,

     *     then {@link SecurityManager#checkPackageAccess

     *     smgr.checkPackageAccess(defcPkg)} is called,

     *     where {@code defcPkg} is the package of {@code defc}.

     * </ul>

     * Security checks are performed after other access checks have passed.

     * Therefore, the above rules presuppose a member or class that is public,

     * or else that is being accessed from a lookup class that has

     * rights to access the member or class.

     *

     * <h1><a name="callsens"></a>Caller sensitive methods</h1>

     * A small number of Java methods have a special property called caller sensitivity.

     * A <em>caller-sensitive</em> method can behave differently depending on the

     * identity of its immediate caller.

     * <p>

     * If a method handle for a caller-sensitive method is requested,

     * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,

     * but they take account of the lookup class in a special way.

     * The resulting method handle behaves as if it were called