/*
 * Copyright (c) 2003, 2019, 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,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javac.code;

import java.lang.ref.SoftReference;
import java.util.HashSet;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.function.BiPredicate;
import java.util.function.Function;
import java.util.stream.Collector;

import javax.tools.JavaFileObject;

import com.sun.tools.javac.code.Attribute.RetentionPolicy;
import com.sun.tools.javac.code.Lint.LintCategory;
import com.sun.tools.javac.code.Source.Feature;
import com.sun.tools.javac.code.Type.UndetVar.InferenceBound;
import com.sun.tools.javac.code.TypeMetadata.Entry.Kind;
import com.sun.tools.javac.comp.AttrContext;
import com.sun.tools.javac.comp.Check;
import com.sun.tools.javac.comp.Enter;
import com.sun.tools.javac.comp.Env;
import com.sun.tools.javac.util.*;

import static com.sun.tools.javac.code.BoundKind.*;
import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Kinds.Kind.*;
import static com.sun.tools.javac.code.Scope.*;
import static com.sun.tools.javac.code.Scope.LookupKind.NON_RECURSIVE;
import static com.sun.tools.javac.code.Symbol.*;
import static com.sun.tools.javac.code.Type.*;
import static com.sun.tools.javac.code.TypeTag.*;
import static com.sun.tools.javac.jvm.ClassFile.externalize;
import com.sun.tools.javac.resources.CompilerProperties.Fragments;

Utility class containing various operations on types.
Unless other names are more illustrative, the following naming
conventions should be observed in this file:

t
If the first argument to an operation is a type, it should be named t.
s
Similarly, if the second argument to an operation is a type, it should be named s.
ts
If an operations takes a list of types, the first should be named ts.
ss
A second list of types should be named ss.

This is NOT part of any supported API.
If you write code that depends on this, you do so at your own risk.
This code and its internal interfaces are subject to change or
deletion without notice.
/**
 * Utility class containing various operations on types.
 *
 * <p>Unless other names are more illustrative, the following naming
 * conventions should be observed in this file:
 *
 * <dl>
 * <dt>t</dt>
 * <dd>If the first argument to an operation is a type, it should be named t.</dd>
 * <dt>s</dt>
 * <dd>Similarly, if the second argument to an operation is a type, it should be named s.</dd>
 * <dt>ts</dt>
 * <dd>If an operations takes a list of types, the first should be named ts.</dd>
 * <dt>ss</dt>
 * <dd>A second list of types should be named ss.</dd>
 * </dl>
 *
 * <p><b>This is NOT part of any supported API.
 * If you write code that depends on this, you do so at your own risk.
 * This code and its internal interfaces are subject to change or
 * deletion without notice.</b>
 */
public class Types {
    protected static final Context.Key<Types> typesKey = new Context.Key<>();

    final Symtab syms;
    final JavacMessages messages;
    final Names names;
    final boolean allowObjectToPrimitiveCast;
    final boolean allowDefaultMethods;
    final boolean mapCapturesToBounds;
    final Check chk;
    final Enter enter;
    JCDiagnostic.Factory diags;
    List<Warner> warnStack = List.nil();
    final Name capturedName;

    public final Warner noWarnings;

    // <editor-fold defaultstate="collapsed" desc="Instantiating">
    public static Types instance(Context context) {
        Types instance = context.get(typesKey);
        if (instance == null)
            instance = new Types(context);
        return instance;
    }

    protected Types(Context context) {
        context.put(typesKey, this);
        syms = Symtab.instance(context);
        names = Names.instance(context);
        Source source = Source.instance(context);
        allowObjectToPrimitiveCast = Feature.OBJECT_TO_PRIMITIVE_CAST.allowedInSource(source);
        allowDefaultMethods = Feature.DEFAULT_METHODS.allowedInSource(source);
        mapCapturesToBounds = Feature.MAP_CAPTURES_TO_BOUNDS.allowedInSource(source);
        chk = Check.instance(context);
        enter = Enter.instance(context);
        capturedName = names.fromString("<captured wildcard>");
        messages = JavacMessages.instance(context);
        diags = JCDiagnostic.Factory.instance(context);
        noWarnings = new Warner(null);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="bounds">
    
Get a wildcard's upper bound, returning non-wildcards unchanged.
Params:
t – a type argument, either a wildcard or a type/**
     * Get a wildcard's upper bound, returning non-wildcards unchanged.
     * @param t a type argument, either a wildcard or a type
     */
    public Type wildUpperBound(Type t) {
        if (t.hasTag(WILDCARD)) {
            WildcardType w = (WildcardType) t;
            if (w.isSuperBound())
                return w.bound == null ? syms.objectType : w.bound.getUpperBound();
            else
                return wildUpperBound(w.type);
        }
        else return t;
    }

    
Get a capture variable's upper bound, returning other types unchanged.
Params:
t – a type/**
     * Get a capture variable's upper bound, returning other types unchanged.
     * @param t a type
     */
    public Type cvarUpperBound(Type t) {
        if (t.hasTag(TYPEVAR)) {
            TypeVar v = (TypeVar) t;
            return v.isCaptured() ? cvarUpperBound(v.getUpperBound()) : v;
        }
        else return t;
    }

    
Get a wildcard's lower bound, returning non-wildcards unchanged.
Params:
t – a type argument, either a wildcard or a type/**
     * Get a wildcard's lower bound, returning non-wildcards unchanged.
     * @param t a type argument, either a wildcard or a type
     */
    public Type wildLowerBound(Type t) {
        if (t.hasTag(WILDCARD)) {
            WildcardType w = (WildcardType) t;
            return w.isExtendsBound() ? syms.botType : wildLowerBound(w.type);
        }
        else return t;
    }

    
Get a capture variable's lower bound, returning other types unchanged.
Params:
t – a type/**
     * Get a capture variable's lower bound, returning other types unchanged.
     * @param t a type
     */
    public Type cvarLowerBound(Type t) {
        if (t.hasTag(TYPEVAR) && ((TypeVar) t).isCaptured()) {
            return cvarLowerBound(t.getLowerBound());
        }
        else return t;
    }

    
Recursively skip type-variables until a class/array type is found; capture conversion is then
(optionally) applied to the resulting type. This is useful for i.e. computing a site that is
suitable for a method lookup.
/**
     * Recursively skip type-variables until a class/array type is found; capture conversion is then
     * (optionally) applied to the resulting type. This is useful for i.e. computing a site that is
     * suitable for a method lookup.
     */
    public Type skipTypeVars(Type site, boolean capture) {
        while (site.hasTag(TYPEVAR)) {
            site = site.getUpperBound();
        }
        return capture ? capture(site) : site;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="projections">

    
A projection kind. See TypeProjection /**
     * A projection kind. See {@link TypeProjection}
     */
    enum ProjectionKind {
        UPWARDS() {
            @Override
            ProjectionKind complement() {
                return DOWNWARDS;
            }
        },
        DOWNWARDS() {
            @Override
            ProjectionKind complement() {
                return UPWARDS;
            }
        };

        abstract ProjectionKind complement();
    }

    
This visitor performs upwards and downwards projections on types. A projection is defined as a function that takes a type T, a set of type variables V and that produces another type S. An upwards projection maps a type T into a type S such that (i) T has no variables in V, and (ii) S is an upper bound of T. A downwards projection maps a type T into a type S such that (i) T has no variables in V, and (ii) S is a lower bound of T. Note that projections are only allowed to touch variables in V. Theferore it is possible for a projection to leave its input type unchanged if it does not contain any variables in V. Moreover, note that while an upwards projection is always defined (every type as an upper bound), a downwards projection is not always defined. Examples: upwards(List<#CAP1>, [#CAP1]) = List<? extends String>, where #CAP1 <: String  downwards(List<#CAP2>, [#CAP2]) = List<? super String>, where #CAP2 :> String  upwards(List<#CAP1>, [#CAP2]) = List<#CAP1>  downwards(List<#CAP1>, [#CAP1]) = not defined  /**
     * This visitor performs upwards and downwards projections on types.
     *
     * A projection is defined as a function that takes a type T, a set of type variables V and that
     * produces another type S.
     *
     * An upwards projection maps a type T into a type S such that (i) T has no variables in V,
     * and (ii) S is an upper bound of T.
     *
     * A downwards projection maps a type T into a type S such that (i) T has no variables in V,
     * and (ii) S is a lower bound of T.
     *
     * Note that projections are only allowed to touch variables in V. Theferore it is possible for
     * a projection to leave its input type unchanged if it does not contain any variables in V.
     *
     * Moreover, note that while an upwards projection is always defined (every type as an upper bound),
     * a downwards projection is not always defined.
     *
     * Examples:
     *
     * {@code upwards(List<#CAP1>, [#CAP1]) = List<? extends String>, where #CAP1 <: String }
     * {@code downwards(List<#CAP2>, [#CAP2]) = List<? super String>, where #CAP2 :> String }
     * {@code upwards(List<#CAP1>, [#CAP2]) = List<#CAP1> }
     * {@code downwards(List<#CAP1>, [#CAP1]) = not defined }
     */
    class TypeProjection extends TypeMapping<ProjectionKind> {

        List<Type> vars;
        Set<Type> seen = new HashSet<>();

        public TypeProjection(List<Type> vars) {
            this.vars = vars;
        }

        @Override
        public Type visitClassType(ClassType t, ProjectionKind pkind) {
            if (t.isCompound()) {
                List<Type> components = directSupertypes(t);
                List<Type> components1 = components.map(c -> c.map(this, pkind));
                if (components == components1) return t;
                else return makeIntersectionType(components1);
            } else {
                Type outer = t.getEnclosingType();
                Type outer1 = visit(outer, pkind);
                List<Type> typarams = t.getTypeArguments();
                List<Type> formals = t.tsym.type.getTypeArguments();
                ListBuffer<Type> typarams1 = new ListBuffer<>();
                boolean changed = false;
                for (Type actual : typarams) {
                    Type t2 = mapTypeArgument(t, formals.head.getUpperBound(), actual, pkind);
                    if (t2.hasTag(BOT)) {
                        //not defined
                        return syms.botType;
                    }
                    typarams1.add(t2);
                    changed |= actual != t2;
                    formals = formals.tail;
                }
                if (outer1 == outer && !changed) return t;
                else return new ClassType(outer1, typarams1.toList(), t.tsym, t.getMetadata()) {
                    @Override
                    protected boolean needsStripping() {
                        return true;
                    }
                };
            }
        }

        @Override
        public Type visitArrayType(ArrayType t, ProjectionKind s) {
            Type elemtype = t.elemtype;
            Type elemtype1 = visit(elemtype, s);
            if (elemtype1 == elemtype) {
                return t;
            } else if (elemtype1.hasTag(BOT)) {
                //undefined
                return syms.botType;
            } else {
                return new ArrayType(elemtype1, t.tsym, t.metadata) {
                    @Override
                    protected boolean needsStripping() {
                        return true;
                    }
                };
            }
        }

        @Override
        public Type visitTypeVar(TypeVar t, ProjectionKind pkind) {
            if (vars.contains(t)) {
                if (seen.add(t)) {
                    try {
                        final Type bound;
                        switch (pkind) {
                            case UPWARDS:
                                bound = t.getUpperBound();
                                break;
                            case DOWNWARDS:
                                bound = (t.getLowerBound() == null) ?
                                        syms.botType :
                                        t.getLowerBound();
                                break;
                            default:
                                Assert.error();
                                return null;
                        }
                        return bound.map(this, pkind);
                    } finally {
                        seen.remove(t);
                    }
                } else {
                    //cycle
                    return pkind == ProjectionKind.UPWARDS ?
                            syms.objectType : syms.botType;
                }
            } else {
                return t;
            }
        }

        private Type mapTypeArgument(Type site, Type declaredBound, Type t, ProjectionKind pkind) {
            return t.containsAny(vars) ?
                    t.map(new TypeArgumentProjection(site, declaredBound), pkind) :
                    t;
        }

        class TypeArgumentProjection extends TypeMapping<ProjectionKind> {

            Type site;
            Type declaredBound;

            TypeArgumentProjection(Type site, Type declaredBound) {
                this.site = site;
                this.declaredBound = declaredBound;
            }

            @Override
            public Type visitType(Type t, ProjectionKind pkind) {
                //type argument is some type containing restricted vars
                if (pkind == ProjectionKind.DOWNWARDS) {
                    //not defined
                    return syms.botType;
                }
                Type upper = t.map(TypeProjection.this, ProjectionKind.UPWARDS);
                Type lower = t.map(TypeProjection.this, ProjectionKind.DOWNWARDS);
                List<Type> formals = site.tsym.type.getTypeArguments();
                BoundKind bk;
                Type bound;
                if (!isSameType(upper, syms.objectType) &&
                        (declaredBound.containsAny(formals) ||
                         !isSubtype(declaredBound, upper))) {
                    bound = upper;
                    bk = EXTENDS;
                } else if (!lower.hasTag(BOT)) {
                    bound = lower;
                    bk = SUPER;
                } else {
                    bound = syms.objectType;
                    bk = UNBOUND;
                }
                return makeWildcard(bound, bk);
            }

            @Override
            public Type visitWildcardType(WildcardType wt, ProjectionKind pkind) {
                //type argument is some wildcard whose bound contains restricted vars
                Type bound = syms.botType;
                BoundKind bk = wt.kind;
                switch (wt.kind) {
                    case EXTENDS:
                        bound = wt.type.map(TypeProjection.this, pkind);
                        if (bound.hasTag(BOT)) {
                            return syms.botType;
                        }
                        break;
                    case SUPER:
                        bound = wt.type.map(TypeProjection.this, pkind.complement());
                        if (bound.hasTag(BOT)) {
                            bound = syms.objectType;
                            bk = UNBOUND;
                        }
                        break;
                }
                return makeWildcard(bound, bk);
            }

            private Type makeWildcard(Type bound, BoundKind bk) {
                return new WildcardType(bound, bk, syms.boundClass) {
                    @Override
                    protected boolean needsStripping() {
                        return true;
                    }
                };
            }
        }
    }

    
Computes an upward projection of given type, and vars. See TypeProjection. 
Params:
t – the type to be projected
vars – the set of type variables to be mapped
Returns:
the type obtained as result of the projection/**
     * Computes an upward projection of given type, and vars. See {@link TypeProjection}.
     *
     * @param t the type to be projected
     * @param vars the set of type variables to be mapped
     * @return the type obtained as result of the projection
     */
    public Type upward(Type t, List<Type> vars) {
        return t.map(new TypeProjection(vars), ProjectionKind.UPWARDS);
    }

    
Computes the set of captured variables mentioned in a given type. See CaptureScanner. This routine is typically used to computed the input set of variables to be used during an upwards projection (see upward(Type, List<Type>)). 
Params:
t – the type where occurrences of captured variables have to be found
Returns:
the set of captured variables found in t/**
     * Computes the set of captured variables mentioned in a given type. See {@link CaptureScanner}.
     * This routine is typically used to computed the input set of variables to be used during
     * an upwards projection (see {@link Types#upward(Type, List)}).
     *
     * @param t the type where occurrences of captured variables have to be found
     * @return the set of captured variables found in t
     */
    public List<Type> captures(Type t) {
        CaptureScanner cs = new CaptureScanner();
        Set<Type> captures = new HashSet<>();
        cs.visit(t, captures);
        return List.from(captures);
    }

    
This visitor scans a type recursively looking for occurrences of captured type variables.
/**
     * This visitor scans a type recursively looking for occurrences of captured type variables.
     */
    class CaptureScanner extends SimpleVisitor<Void, Set<Type>> {

        @Override
        public Void visitType(Type t, Set<Type> types) {
            return null;
        }

        @Override
        public Void visitClassType(ClassType t, Set<Type> seen) {
            if (t.isCompound()) {
                directSupertypes(t).forEach(s -> visit(s, seen));
            } else {
                t.allparams().forEach(ta -> visit(ta, seen));
            }
            return null;
        }

        @Override
        public Void visitArrayType(ArrayType t, Set<Type> seen) {
            return visit(t.elemtype, seen);
        }

        @Override
        public Void visitWildcardType(WildcardType t, Set<Type> seen) {
            visit(t.type, seen);
            return null;
        }

        @Override
        public Void visitTypeVar(TypeVar t, Set<Type> seen) {
            if ((t.tsym.flags() & Flags.SYNTHETIC) != 0 && seen.add(t)) {
                visit(t.getUpperBound(), seen);
            }
            return null;
        }

        @Override
        public Void visitCapturedType(CapturedType t, Set<Type> seen) {
            if (seen.add(t)) {
                visit(t.getUpperBound(), seen);
                visit(t.getLowerBound(), seen);
            }
            return null;
        }
    }

    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isUnbounded">
    
Checks that all the arguments to a class are unbounded
wildcards or something else that doesn't make any restrictions
on the arguments. If a class isUnbounded, a raw super- or
subclass can be cast to it without a warning.
Params:
t – a type
Returns:
true iff the given type is unbounded or raw/**
     * Checks that all the arguments to a class are unbounded
     * wildcards or something else that doesn't make any restrictions
     * on the arguments. If a class isUnbounded, a raw super- or
     * subclass can be cast to it without a warning.
     * @param t a type
     * @return true iff the given type is unbounded or raw
     */
    public boolean isUnbounded(Type t) {
        return isUnbounded.visit(t);
    }
    // where
        private final UnaryVisitor<Boolean> isUnbounded = new UnaryVisitor<Boolean>() {

            public Boolean visitType(Type t, Void ignored) {
                return true;
            }

            @Override
            public Boolean visitClassType(ClassType t, Void ignored) {
                List<Type> parms = t.tsym.type.allparams();
                List<Type> args = t.allparams();
                while (parms.nonEmpty()) {
                    WildcardType unb = new WildcardType(syms.objectType,
                                                        BoundKind.UNBOUND,
                                                        syms.boundClass,
                                                        (TypeVar)parms.head);
                    if (!containsType(args.head, unb))
                        return false;
                    parms = parms.tail;
                    args = args.tail;
                }
                return true;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="asSub">
    
Return the least specific subtype of t that starts with symbol
sym.  If none exists, return null.  The least specific subtype
is determined as follows:
If there is exactly one parameterized instance of sym that is a
subtype of t, that parameterized instance is returned.

Otherwise, if the plain type or raw type `sym' is a subtype of
type t, the type `sym' itself is returned.  Otherwise, null is
returned.
/**
     * Return the least specific subtype of t that starts with symbol
     * sym.  If none exists, return null.  The least specific subtype
     * is determined as follows:
     *
     * <p>If there is exactly one parameterized instance of sym that is a
     * subtype of t, that parameterized instance is returned.<br>
     * Otherwise, if the plain type or raw type `sym' is a subtype of
     * type t, the type `sym' itself is returned.  Otherwise, null is
     * returned.
     */
    public Type asSub(Type t, Symbol sym) {
        return asSub.visit(t, sym);
    }
    // where
        private final SimpleVisitor<Type,Symbol> asSub = new SimpleVisitor<Type,Symbol>() {

            public Type visitType(Type t, Symbol sym) {
                return null;
            }

            @Override
            public Type visitClassType(ClassType t, Symbol sym) {
                if (t.tsym == sym)
                    return t;
                Type base = asSuper(sym.type, t.tsym);
                if (base == null)
                    return null;
                ListBuffer<Type> from = new ListBuffer<>();
                ListBuffer<Type> to = new ListBuffer<>();
                try {
                    adapt(base, t, from, to);
                } catch (AdaptFailure ex) {
                    return null;
                }
                Type res = subst(sym.type, from.toList(), to.toList());
                if (!isSubtype(res, t))
                    return null;
                ListBuffer<Type> openVars = new ListBuffer<>();
                for (List<Type> l = sym.type.allparams();
                     l.nonEmpty(); l = l.tail)
                    if (res.contains(l.head) && !t.contains(l.head))
                        openVars.append(l.head);
                if (openVars.nonEmpty()) {
                    if (t.isRaw()) {
                        // The subtype of a raw type is raw
                        res = erasure(res);
                    } else {
                        // Unbound type arguments default to ?
                        List<Type> opens = openVars.toList();
                        ListBuffer<Type> qs = new ListBuffer<>();
                        for (List<Type> iter = opens; iter.nonEmpty(); iter = iter.tail) {
                            qs.append(new WildcardType(syms.objectType, BoundKind.UNBOUND,
                                                       syms.boundClass, (TypeVar) iter.head));
                        }
                        res = subst(res, opens, qs.toList());
                    }
                }
                return res;
            }

            @Override
            public Type visitErrorType(ErrorType t, Symbol sym) {
                return t;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isConvertible">
    
Is t a subtype of or convertible via boxing/unboxing
conversion to s?
/**
     * Is t a subtype of or convertible via boxing/unboxing
     * conversion to s?
     */
    public boolean isConvertible(Type t, Type s, Warner warn) {
        if (t.hasTag(ERROR)) {
            return true;
        }
        boolean tPrimitive = t.isPrimitive();
        boolean sPrimitive = s.isPrimitive();
        if (tPrimitive == sPrimitive) {
            return isSubtypeUnchecked(t, s, warn);
        }
        boolean tUndet = t.hasTag(UNDETVAR);
        boolean sUndet = s.hasTag(UNDETVAR);

        if (tUndet || sUndet) {
            return tUndet ?
                    isSubtype(t, boxedTypeOrType(s)) :
                    isSubtype(boxedTypeOrType(t), s);
        }

        return tPrimitive
            ? isSubtype(boxedClass(t).type, s)
            : isSubtype(unboxedType(t), s);
    }

    
Is t a subtype of or convertible via boxing/unboxing
conversions to s?
/**
     * Is t a subtype of or convertible via boxing/unboxing
     * conversions to s?
     */
    public boolean isConvertible(Type t, Type s) {
        return isConvertible(t, s, noWarnings);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="findSam">

    
Exception used to report a function descriptor lookup failure. The exception
wraps a diagnostic that can be used to generate more details error
messages.
/**
     * Exception used to report a function descriptor lookup failure. The exception
     * wraps a diagnostic that can be used to generate more details error
     * messages.
     */
    public static class FunctionDescriptorLookupError extends RuntimeException {
        private static final long serialVersionUID = 0;

        JCDiagnostic diagnostic;

        FunctionDescriptorLookupError() {
            this.diagnostic = null;
        }

        FunctionDescriptorLookupError setMessage(JCDiagnostic diag) {
            this.diagnostic = diag;
            return this;
        }

        public JCDiagnostic getDiagnostic() {
            return diagnostic;
        }
    }

    
A cache that keeps track of function descriptors associated with given
functional interfaces.
/**
     * A cache that keeps track of function descriptors associated with given
     * functional interfaces.
     */
    class DescriptorCache {

        private WeakHashMap<TypeSymbol, Entry> _map = new WeakHashMap<>();

        class FunctionDescriptor {
            Symbol descSym;

            FunctionDescriptor(Symbol descSym) {
                this.descSym = descSym;
            }

            public Symbol getSymbol() {
                return descSym;
            }

            public Type getType(Type site) {
                site = removeWildcards(site);
                if (site.isIntersection()) {
                    IntersectionClassType ict = (IntersectionClassType)site;
                    for (Type component : ict.getExplicitComponents()) {
                        if (!chk.checkValidGenericType(component)) {
                            //if the inferred functional interface type is not well-formed,
                            //or if it's not a subtype of the original target, issue an error
                            throw failure(diags.fragment(Fragments.NoSuitableFunctionalIntfInst(site)));
                        }
                    }
                } else {
                    if (!chk.checkValidGenericType(site)) {
                        //if the inferred functional interface type is not well-formed,
                        //or if it's not a subtype of the original target, issue an error
                        throw failure(diags.fragment(Fragments.NoSuitableFunctionalIntfInst(site)));
                    }
                }
                return memberType(site, descSym);
            }
        }

        class Entry {
            final FunctionDescriptor cachedDescRes;
            final int prevMark;

            public Entry(FunctionDescriptor cachedDescRes,
                    int prevMark) {
                this.cachedDescRes = cachedDescRes;
                this.prevMark = prevMark;
            }

            boolean matches(int mark) {
                return  this.prevMark == mark;
            }
        }

        FunctionDescriptor get(TypeSymbol origin) throws FunctionDescriptorLookupError {
            Entry e = _map.get(origin);
            CompoundScope members = membersClosure(origin.type, false);
            if (e == null ||
                    !e.matches(members.getMark())) {
                FunctionDescriptor descRes = findDescriptorInternal(origin, members);
                _map.put(origin, new Entry(descRes, members.getMark()));
                return descRes;
            }
            else {
                return e.cachedDescRes;
            }
        }

        
Compute the function descriptor associated with a given functional interface
/**
         * Compute the function descriptor associated with a given functional interface
         */
        public FunctionDescriptor findDescriptorInternal(TypeSymbol origin,
                CompoundScope membersCache) throws FunctionDescriptorLookupError {
            if (!origin.isInterface() || (origin.flags() & ANNOTATION) != 0) {
                //t must be an interface
                throw failure("not.a.functional.intf", origin);
            }

            final ListBuffer<Symbol> abstracts = new ListBuffer<>();
            for (Symbol sym : membersCache.getSymbols(new DescriptorFilter(origin))) {
                Type mtype = memberType(origin.type, sym);
                if (abstracts.isEmpty()) {
                    abstracts.append(sym);
                } else if ((sym.name == abstracts.first().name &&
                        overrideEquivalent(mtype, memberType(origin.type, abstracts.first())))) {
                    if (!abstracts.stream().filter(msym -> msym.owner.isSubClass(sym.enclClass(), Types.this))
                            .map(msym -> memberType(origin.type, msym))
                            .anyMatch(abstractMType -> isSubSignature(abstractMType, mtype))) {
                        abstracts.append(sym);
                    }
                } else {
                    //the target method(s) should be the only abstract members of t
                    throw failure("not.a.functional.intf.1",  origin,
                            diags.fragment(Fragments.IncompatibleAbstracts(Kinds.kindName(origin), origin)));
                }
            }
            if (abstracts.isEmpty()) {
                //t must define a suitable non-generic method
                throw failure("not.a.functional.intf.1", origin,
                            diags.fragment(Fragments.NoAbstracts(Kinds.kindName(origin), origin)));
            } else if (abstracts.size() == 1) {
                return new FunctionDescriptor(abstracts.first());
            } else { // size > 1
                FunctionDescriptor descRes = mergeDescriptors(origin, abstracts.toList());
                if (descRes == null) {
                    //we can get here if the functional interface is ill-formed
                    ListBuffer<JCDiagnostic> descriptors = new ListBuffer<>();
                    for (Symbol desc : abstracts) {
                        String key = desc.type.getThrownTypes().nonEmpty() ?
                                "descriptor.throws" : "descriptor";
                        descriptors.append(diags.fragment(key, desc.name,
                                desc.type.getParameterTypes(),
                                desc.type.getReturnType(),
                                desc.type.getThrownTypes()));
                    }
                    JCDiagnostic msg =
                            diags.fragment(Fragments.IncompatibleDescsInFunctionalIntf(Kinds.kindName(origin),
                                                                                       origin));
                    JCDiagnostic.MultilineDiagnostic incompatibleDescriptors =
                            new JCDiagnostic.MultilineDiagnostic(msg, descriptors.toList());
                    throw failure(incompatibleDescriptors);
                }
                return descRes;
            }
        }

        
Compute a synthetic type for the target descriptor given a list
of override-equivalent methods in the functional interface type.
The resulting method type is a method type that is override-equivalent
and return-type substitutable with each method in the original list.
/**
         * Compute a synthetic type for the target descriptor given a list
         * of override-equivalent methods in the functional interface type.
         * The resulting method type is a method type that is override-equivalent
         * and return-type substitutable with each method in the original list.
         */
        private FunctionDescriptor mergeDescriptors(TypeSymbol origin, List<Symbol> methodSyms) {
            return mergeAbstracts(methodSyms, origin.type, false)
                    .map(bestSoFar -> new FunctionDescriptor(bestSoFar.baseSymbol()) {
                        @Override
                        public Type getType(Type origin) {
                            Type mt = memberType(origin, getSymbol());
                            return createMethodTypeWithThrown(mt, bestSoFar.type.getThrownTypes());
                        }
                    }).orElse(null);
        }

        FunctionDescriptorLookupError failure(String msg, Object... args) {
            return failure(diags.fragment(msg, args));
        }

        FunctionDescriptorLookupError failure(JCDiagnostic diag) {
            return new FunctionDescriptorLookupError().setMessage(diag);
        }
    }

    private DescriptorCache descCache = new DescriptorCache();

    
Find the method descriptor associated to this class symbol - if the
symbol 'origin' is not a functional interface, an exception is thrown.
/**
     * Find the method descriptor associated to this class symbol - if the
     * symbol 'origin' is not a functional interface, an exception is thrown.
     */
    public Symbol findDescriptorSymbol(TypeSymbol origin) throws FunctionDescriptorLookupError {
        return descCache.get(origin).getSymbol();
    }

    
Find the type of the method descriptor associated to this class symbol -
if the symbol 'origin' is not a functional interface, an exception is thrown.
/**
     * Find the type of the method descriptor associated to this class symbol -
     * if the symbol 'origin' is not a functional interface, an exception is thrown.
     */
    public Type findDescriptorType(Type origin) throws FunctionDescriptorLookupError {
        return descCache.get(origin.tsym).getType(origin);
    }

    
Is given type a functional interface?
/**
     * Is given type a functional interface?
     */
    public boolean isFunctionalInterface(TypeSymbol tsym) {
        try {
            findDescriptorSymbol(tsym);
            return true;
        } catch (FunctionDescriptorLookupError ex) {
            return false;
        }
    }

    public boolean isFunctionalInterface(Type site) {
        try {
            findDescriptorType(site);
            return true;
        } catch (FunctionDescriptorLookupError ex) {
            return false;
        }
    }

    public Type removeWildcards(Type site) {
        if (site.getTypeArguments().stream().anyMatch(t -> t.hasTag(WILDCARD))) {
            //compute non-wildcard parameterization - JLS 9.9
            List<Type> actuals = site.getTypeArguments();
            List<Type> formals = site.tsym.type.getTypeArguments();
            ListBuffer<Type> targs = new ListBuffer<>();
            for (Type formal : formals) {
                Type actual = actuals.head;
                Type bound = formal.getUpperBound();
                if (actuals.head.hasTag(WILDCARD)) {
                    WildcardType wt = (WildcardType)actual;
                    //check that bound does not contain other formals
                    if (bound.containsAny(formals)) {
                        targs.add(wt.type);
                    } else {
                        //compute new type-argument based on declared bound and wildcard bound
                        switch (wt.kind) {
                            case UNBOUND:
                                targs.add(bound);
                                break;
                            case EXTENDS:
                                targs.add(glb(bound, wt.type));
                                break;
                            case SUPER:
                                targs.add(wt.type);
                                break;
                            default:
                                Assert.error("Cannot get here!");
                        }
                    }
                } else {
                    //not a wildcard - the new type argument remains unchanged
                    targs.add(actual);
                }
                actuals = actuals.tail;
            }
            return subst(site.tsym.type, formals, targs.toList());
        } else {
            return site;
        }
    }

    
Create a symbol for a class that implements a given functional interface
and overrides its functional descriptor. This routine is used for two
main purposes: (i) checking well-formedness of a functional interface;
(ii) perform functional interface bridge calculation.
/**
     * Create a symbol for a class that implements a given functional interface
     * and overrides its functional descriptor. This routine is used for two
     * main purposes: (i) checking well-formedness of a functional interface;
     * (ii) perform functional interface bridge calculation.
     */
    public ClassSymbol makeFunctionalInterfaceClass(Env<AttrContext> env, Name name, Type target, long cflags) {
        if (target == null || target == syms.unknownType) {
            return null;
        }
        Symbol descSym = findDescriptorSymbol(target.tsym);
        Type descType = findDescriptorType(target);
        ClassSymbol csym = new ClassSymbol(cflags, name, env.enclClass.sym.outermostClass());
        csym.completer = Completer.NULL_COMPLETER;
        csym.members_field = WriteableScope.create(csym);
        MethodSymbol instDescSym = new MethodSymbol(descSym.flags(), descSym.name, descType, csym);
        csym.members_field.enter(instDescSym);
        Type.ClassType ctype = new Type.ClassType(Type.noType, List.nil(), csym);
        ctype.supertype_field = syms.objectType;
        ctype.interfaces_field = target.isIntersection() ?
                directSupertypes(target) :
                List.of(target);
        csym.type = ctype;
        csym.sourcefile = ((ClassSymbol)csym.owner).sourcefile;
        return csym;
    }

    
Find the minimal set of methods that are overridden by the functional
descriptor in 'origin'. All returned methods are assumed to have different
erased signatures.
/**
     * Find the minimal set of methods that are overridden by the functional
     * descriptor in 'origin'. All returned methods are assumed to have different
     * erased signatures.
     */
    public List<Symbol> functionalInterfaceBridges(TypeSymbol origin) {
        Assert.check(isFunctionalInterface(origin));
        Symbol descSym = findDescriptorSymbol(origin);
        CompoundScope members = membersClosure(origin.type, false);
        ListBuffer<Symbol> overridden = new ListBuffer<>();
        outer: for (Symbol m2 : members.getSymbolsByName(descSym.name, bridgeFilter)) {
            if (m2 == descSym) continue;
            else if (descSym.overrides(m2, origin, Types.this, false)) {
                for (Symbol m3 : overridden) {
                    if (isSameType(m3.erasure(Types.this), m2.erasure(Types.this)) ||
                            (m3.overrides(m2, origin, Types.this, false) &&
                            (pendingBridges((ClassSymbol)origin, m3.enclClass()) ||
                            (((MethodSymbol)m2).binaryImplementation((ClassSymbol)m3.owner, Types.this) != null)))) {
                        continue outer;
                    }
                }
                overridden.add(m2);
            }
        }
        return overridden.toList();
    }
    //where
        private Filter<Symbol> bridgeFilter = new Filter<Symbol>() {
            public boolean accepts(Symbol t) {
                return t.kind == MTH &&
                        t.name != names.init &&
                        t.name != names.clinit &&
                        (t.flags() & SYNTHETIC) == 0;
            }
        };
        private boolean pendingBridges(ClassSymbol origin, TypeSymbol s) {
            //a symbol will be completed from a classfile if (a) symbol has
            //an associated file object with CLASS kind and (b) the symbol has
            //not been entered
            if (origin.classfile != null &&
                    origin.classfile.getKind() == JavaFileObject.Kind.CLASS &&
                    enter.getEnv(origin) == null) {
                return false;
            }
            if (origin == s) {
                return true;
            }
            for (Type t : interfaces(origin.type)) {
                if (pendingBridges((ClassSymbol)t.tsym, s)) {
                    return true;
                }
            }
            return false;
        }
    // </editor-fold>

   
Scope filter used to skip methods that should be ignored (such as methods
overridden by j.l.Object) during function interface conversion interface check
/**
    * Scope filter used to skip methods that should be ignored (such as methods
    * overridden by j.l.Object) during function interface conversion interface check
    */
    class DescriptorFilter implements Filter<Symbol> {

       TypeSymbol origin;

       DescriptorFilter(TypeSymbol origin) {
           this.origin = origin;
       }

       @Override
       public boolean accepts(Symbol sym) {
           return sym.kind == MTH &&
                   (sym.flags() & (ABSTRACT | DEFAULT)) == ABSTRACT &&
                   !overridesObjectMethod(origin, sym) &&
                   (interfaceCandidates(origin.type, (MethodSymbol)sym).head.flags() & DEFAULT) == 0;
       }
    }

    // <editor-fold defaultstate="collapsed" desc="isSubtype">
    
Is t an unchecked subtype of s?
/**
     * Is t an unchecked subtype of s?
     */
    public boolean isSubtypeUnchecked(Type t, Type s) {
        return isSubtypeUnchecked(t, s, noWarnings);
    }
    
Is t an unchecked subtype of s?
/**
     * Is t an unchecked subtype of s?
     */
    public boolean isSubtypeUnchecked(Type t, Type s, Warner warn) {
        boolean result = isSubtypeUncheckedInternal(t, s, true, warn);
        if (result) {
            checkUnsafeVarargsConversion(t, s, warn);
        }
        return result;
    }
    //where
        private boolean isSubtypeUncheckedInternal(Type t, Type s, boolean capture, Warner warn) {
            if (t.hasTag(ARRAY) && s.hasTag(ARRAY)) {
                if (((ArrayType)t).elemtype.isPrimitive()) {
                    return isSameType(elemtype(t), elemtype(s));
                } else {
                    return isSubtypeUncheckedInternal(elemtype(t), elemtype(s), false, warn);
                }
            } else if (isSubtype(t, s, capture)) {
                return true;
            } else if (t.hasTag(TYPEVAR)) {
                return isSubtypeUncheckedInternal(t.getUpperBound(), s, false, warn);
            } else if (!s.isRaw()) {
                Type t2 = asSuper(t, s.tsym);
                if (t2 != null && t2.isRaw()) {
                    if (isReifiable(s)) {
                        warn.silentWarn(LintCategory.UNCHECKED);
                    } else {
                        warn.warn(LintCategory.UNCHECKED);
                    }
                    return true;
                }
            }
            return false;
        }

        private void checkUnsafeVarargsConversion(Type t, Type s, Warner warn) {
            if (!t.hasTag(ARRAY) || isReifiable(t)) {
                return;
            }
            ArrayType from = (ArrayType)t;
            boolean shouldWarn = false;
            switch (s.getTag()) {
                case ARRAY:
                    ArrayType to = (ArrayType)s;
                    shouldWarn = from.isVarargs() &&
                            !to.isVarargs() &&
                            !isReifiable(from);
                    break;
                case CLASS:
                    shouldWarn = from.isVarargs();
                    break;
            }
            if (shouldWarn) {
                warn.warn(LintCategory.VARARGS);
            }
        }

    
Is t a subtype of s?

(not defined for Method and ForAll types)
/**
     * Is t a subtype of s?<br>
     * (not defined for Method and ForAll types)
     */
    final public boolean isSubtype(Type t, Type s) {
        return isSubtype(t, s, true);
    }
    final public boolean isSubtypeNoCapture(Type t, Type s) {
        return isSubtype(t, s, false);
    }
    public boolean isSubtype(Type t, Type s, boolean capture) {
        if (t.equalsIgnoreMetadata(s))
            return true;
        if (s.isPartial())
            return isSuperType(s, t);

        if (s.isCompound()) {
            for (Type s2 : interfaces(s).prepend(supertype(s))) {
                if (!isSubtype(t, s2, capture))
                    return false;
            }
            return true;
        }

        // Generally, if 's' is a lower-bounded type variable, recur on lower bound; but
        // for inference variables and intersections, we need to keep 's'
        // (see JLS 4.10.2 for intersections and 18.2.3 for inference vars)
        if (!t.hasTag(UNDETVAR) && !t.isCompound()) {
            // TODO: JDK-8039198, bounds checking sometimes passes in a wildcard as s
            Type lower = cvarLowerBound(wildLowerBound(s));
            if (s != lower && !lower.hasTag(BOT))
                return isSubtype(capture ? capture(t) : t, lower, false);
        }

        return isSubtype.visit(capture ? capture(t) : t, s);
    }
    // where
        private TypeRelation isSubtype = new TypeRelation()
        {
            @Override
            public Boolean visitType(Type t, Type s) {
                switch (t.getTag()) {
                 case BYTE:
                     return (!s.hasTag(CHAR) && t.getTag().isSubRangeOf(s.getTag()));
                 case CHAR:
                     return (!s.hasTag(SHORT) && t.getTag().isSubRangeOf(s.getTag()));
                 case SHORT: case INT: case LONG:
                 case FLOAT: case DOUBLE:
                     return t.getTag().isSubRangeOf(s.getTag());
                 case BOOLEAN: case VOID:
                     return t.hasTag(s.getTag());
                 case TYPEVAR:
                     return isSubtypeNoCapture(t.getUpperBound(), s);
                 case BOT:
                     return
                         s.hasTag(BOT) || s.hasTag(CLASS) ||
                         s.hasTag(ARRAY) || s.hasTag(TYPEVAR);
                 case WILDCARD: //we shouldn't be here - avoids crash (see 7034495)
                 case NONE:
                     return false;
                 default:
                     throw new AssertionError("isSubtype " + t.getTag());
                 }
            }

            private Set<TypePair> cache = new HashSet<>();

            private boolean containsTypeRecursive(Type t, Type s) {
                TypePair pair = new TypePair(t, s);
                if (cache.add(pair)) {
                    try {
                        return containsType(t.getTypeArguments(),
                                            s.getTypeArguments());
                    } finally {
                        cache.remove(pair);
                    }
                } else {
                    return containsType(t.getTypeArguments(),
                                        rewriteSupers(s).getTypeArguments());
                }
            }

            private Type rewriteSupers(Type t) {
                if (!t.isParameterized())
                    return t;
                ListBuffer<Type> from = new ListBuffer<>();
                ListBuffer<Type> to = new ListBuffer<>();
                adaptSelf(t, from, to);
                if (from.isEmpty())
                    return t;
                ListBuffer<Type> rewrite = new ListBuffer<>();
                boolean changed = false;
                for (Type orig : to.toList()) {
                    Type s = rewriteSupers(orig);
                    if (s.isSuperBound() && !s.isExtendsBound()) {
                        s = new WildcardType(syms.objectType,
                                             BoundKind.UNBOUND,
                                             syms.boundClass,
                                             s.getMetadata());
                        changed = true;
                    } else if (s != orig) {
                        s = new WildcardType(wildUpperBound(s),
                                             BoundKind.EXTENDS,
                                             syms.boundClass,
                                             s.getMetadata());
                        changed = true;
                    }
                    rewrite.append(s);
                }
                if (changed)
                    return subst(t.tsym.type, from.toList(), rewrite.toList());
                else
                    return t;
            }

            @Override
            public Boolean visitClassType(ClassType t, Type s) {
                Type sup = asSuper(t, s.tsym);
                if (sup == null) return false;
                // If t is an intersection, sup might not be a class type
                if (!sup.hasTag(CLASS)) return isSubtypeNoCapture(sup, s);
                return sup.tsym == s.tsym
                     // Check type variable containment
                    && (!s.isParameterized() || containsTypeRecursive(s, sup))
                    && isSubtypeNoCapture(sup.getEnclosingType(),
                                          s.getEnclosingType());
            }

            @Override
            public Boolean visitArrayType(ArrayType t, Type s) {
                if (s.hasTag(ARRAY)) {
                    if (t.elemtype.isPrimitive())
                        return isSameType(t.elemtype, elemtype(s));
                    else
                        return isSubtypeNoCapture(t.elemtype, elemtype(s));
                }

                if (s.hasTag(CLASS)) {
                    Name sname = s.tsym.getQualifiedName();
                    return sname == names.java_lang_Object
                        || sname == names.java_lang_Cloneable
                        || sname == names.java_io_Serializable;
                }

                return false;
            }

            @Override
            public Boolean visitUndetVar(UndetVar t, Type s) {
                //todo: test against origin needed? or replace with substitution?
                if (t == s || t.qtype == s || s.hasTag(ERROR) || s.hasTag(UNKNOWN)) {
                    return true;
                } else if (s.hasTag(BOT)) {
                    //if 's' is 'null' there's no instantiated type U for which
                    //U <: s (but 'null' itself, which is not a valid type)
                    return false;
                }

                t.addBound(InferenceBound.UPPER, s, Types.this);
                return true;
            }

            @Override
            public Boolean visitErrorType(ErrorType t, Type s) {
                return true;
            }
        };

    
Is t a subtype of every type in given list `ts'?

(not defined for Method and ForAll types)

Allows unchecked conversions.
/**
     * Is t a subtype of every type in given list `ts'?<br>
     * (not defined for Method and ForAll types)<br>
     * Allows unchecked conversions.
     */
    public boolean isSubtypeUnchecked(Type t, List<Type> ts, Warner warn) {
        for (List<Type> l = ts; l.nonEmpty(); l = l.tail)
            if (!isSubtypeUnchecked(t, l.head, warn))
                return false;
        return true;
    }

    
Are corresponding elements of ts subtypes of ss?  If lists are
of different length, return false.
/**
     * Are corresponding elements of ts subtypes of ss?  If lists are
     * of different length, return false.
     */
    public boolean isSubtypes(List<Type> ts, List<Type> ss) {
        while (ts.tail != null && ss.tail != null
               /*inlined: ts.nonEmpty() && ss.nonEmpty()*/ &&
               isSubtype(ts.head, ss.head)) {
            ts = ts.tail;
            ss = ss.tail;
        }
        return ts.tail == null && ss.tail == null;
        /*inlined: ts.isEmpty() && ss.isEmpty();*/
    }

    
Are corresponding elements of ts subtypes of ss, allowing
unchecked conversions?  If lists are of different length,
return false.
/**
     * Are corresponding elements of ts subtypes of ss, allowing
     * unchecked conversions?  If lists are of different length,
     * return false.
     **/
    public boolean isSubtypesUnchecked(List<Type> ts, List<Type> ss, Warner warn) {
        while (ts.tail != null && ss.tail != null
               /*inlined: ts.nonEmpty() && ss.nonEmpty()*/ &&
               isSubtypeUnchecked(ts.head, ss.head, warn)) {
            ts = ts.tail;
            ss = ss.tail;
        }
        return ts.tail == null && ss.tail == null;
        /*inlined: ts.isEmpty() && ss.isEmpty();*/
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isSuperType">
    
Is t a supertype of s?
/**
     * Is t a supertype of s?
     */
    public boolean isSuperType(Type t, Type s) {
        switch (t.getTag()) {
        case ERROR:
            return true;
        case UNDETVAR: {
            UndetVar undet = (UndetVar)t;
            if (t == s ||
                undet.qtype == s ||
                s.hasTag(ERROR) ||
                s.hasTag(BOT)) {
                return true;
            }
            undet.addBound(InferenceBound.LOWER, s, this);
            return true;
        }
        default:
            return isSubtype(s, t);
        }
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isSameType">
    
Are corresponding elements of the lists the same type?  If
lists are of different length, return false.
/**
     * Are corresponding elements of the lists the same type?  If
     * lists are of different length, return false.
     */
    public boolean isSameTypes(List<Type> ts, List<Type> ss) {
        while (ts.tail != null && ss.tail != null
               /*inlined: ts.nonEmpty() && ss.nonEmpty()*/ &&
               isSameType(ts.head, ss.head)) {
            ts = ts.tail;
            ss = ss.tail;
        }
        return ts.tail == null && ss.tail == null;
        /*inlined: ts.isEmpty() && ss.isEmpty();*/
    }

    
A polymorphic signature method (JLS 15.12.3) is a method that
  (i) is declared in the java.lang.invoke.MethodHandle/VarHandle classes;
 (ii) takes a single variable arity parameter;
(iii) whose declared type is Object[];
 (iv) has any return type, Object signifying a polymorphic return type; and
  (v) is native.
/**
     * A polymorphic signature method (JLS 15.12.3) is a method that
     *   (i) is declared in the java.lang.invoke.MethodHandle/VarHandle classes;
     *  (ii) takes a single variable arity parameter;
     * (iii) whose declared type is Object[];
     *  (iv) has any return type, Object signifying a polymorphic return type; and
     *   (v) is native.
    */
   public boolean isSignaturePolymorphic(MethodSymbol msym) {
       List<Type> argtypes = msym.type.getParameterTypes();
       return (msym.flags_field & NATIVE) != 0 &&
              (msym.owner == syms.methodHandleType.tsym || msym.owner == syms.varHandleType.tsym) &&
               argtypes.length() == 1 &&
               argtypes.head.hasTag(TypeTag.ARRAY) &&
               ((ArrayType)argtypes.head).elemtype.tsym == syms.objectType.tsym;
   }

    
Is t the same type as s?
/**
     * Is t the same type as s?
     */
    public boolean isSameType(Type t, Type s) {
        return isSameTypeVisitor.visit(t, s);
    }
    // where

        
Type-equality relation - type variables are considered
equals if they share the same object identity.
/**
         * Type-equality relation - type variables are considered
         * equals if they share the same object identity.
         */
        TypeRelation isSameTypeVisitor = new TypeRelation() {

            public Boolean visitType(Type t, Type s) {
                if (t.equalsIgnoreMetadata(s))
                    return true;

                if (s.isPartial())
                    return visit(s, t);

                switch (t.getTag()) {
                case BYTE: case CHAR: case SHORT: case INT: case LONG: case FLOAT:
                case DOUBLE: case BOOLEAN: case VOID: case BOT: case NONE:
                    return t.hasTag(s.getTag());
                case TYPEVAR: {
                    if (s.hasTag(TYPEVAR)) {
                        //type-substitution does not preserve type-var types
                        //check that type var symbols and bounds are indeed the same
                        return t == s;
                    }
                    else {
                        //special case for s == ? super X, where upper(s) = u
                        //check that u == t, where u has been set by Type.withTypeVar
                        return s.isSuperBound() &&
                                !s.isExtendsBound() &&
                                visit(t, wildUpperBound(s));
                    }
                }
                default:
                    throw new AssertionError("isSameType " + t.getTag());
                }
            }

            @Override
            public Boolean visitWildcardType(WildcardType t, Type s) {
                if (!s.hasTag(WILDCARD)) {
                    return false;
                } else {
                    WildcardType t2 = (WildcardType)s;
                    return (t.kind == t2.kind || (t.isExtendsBound() && s.isExtendsBound())) &&
                            isSameType(t.type, t2.type);
                }
            }

            @Override
            public Boolean visitClassType(ClassType t, Type s) {
                if (t == s)
                    return true;

                if (s.isPartial())
                    return visit(s, t);

                if (s.isSuperBound() && !s.isExtendsBound())
                    return visit(t, wildUpperBound(s)) && visit(t, wildLowerBound(s));

                if (t.isCompound() && s.isCompound()) {
                    if (!visit(supertype(t), supertype(s)))
                        return false;

                    Map<Symbol,Type> tMap = new HashMap<>();
                    for (Type ti : interfaces(t)) {
                        if (tMap.containsKey(ti)) {
                            throw new AssertionError("Malformed intersection");
                        }
                        tMap.put(ti.tsym, ti);
                    }
                    for (Type si : interfaces(s)) {
                        if (!tMap.containsKey(si.tsym))
                            return false;
                        Type ti = tMap.remove(si.tsym);
                        if (!visit(ti, si))
                            return false;
                    }
                    return tMap.isEmpty();
                }
                return t.tsym == s.tsym
                    && visit(t.getEnclosingType(), s.getEnclosingType())
                    && containsTypeEquivalent(t.getTypeArguments(), s.getTypeArguments());
            }

            @Override
            public Boolean visitArrayType(ArrayType t, Type s) {
                if (t == s)
                    return true;

                if (s.isPartial())
                    return visit(s, t);

                return s.hasTag(ARRAY)
                    && containsTypeEquivalent(t.elemtype, elemtype(s));
            }

            @Override
            public Boolean visitMethodType(MethodType t, Type s) {
                // isSameType for methods does not take thrown
                // exceptions into account!
                return hasSameArgs(t, s) && visit(t.getReturnType(), s.getReturnType());
            }

            @Override
            public Boolean visitPackageType(PackageType t, Type s) {
                return t == s;
            }

            @Override
            public Boolean visitForAll(ForAll t, Type s) {
                if (!s.hasTag(FORALL)) {
                    return false;
                }

                ForAll forAll = (ForAll)s;
                return hasSameBounds(t, forAll)
                    && visit(t.qtype, subst(forAll.qtype, forAll.tvars, t.tvars));
            }

            @Override
            public Boolean visitUndetVar(UndetVar t, Type s) {
                if (s.hasTag(WILDCARD)) {
                    // FIXME, this might be leftovers from before capture conversion
                    return false;
                }

                if (t == s || t.qtype == s || s.hasTag(ERROR) || s.hasTag(UNKNOWN)) {
                    return true;
                }

                t.addBound(InferenceBound.EQ, s, Types.this);

                return true;
            }

            @Override
            public Boolean visitErrorType(ErrorType t, Type s) {
                return true;
            }
        };

    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Contains Type">
    public boolean containedBy(Type t, Type s) {
        switch (t.getTag()) {
        case UNDETVAR:
            if (s.hasTag(WILDCARD)) {
                UndetVar undetvar = (UndetVar)t;
                WildcardType wt = (WildcardType)s;
                switch(wt.kind) {
                    case UNBOUND:
                        break;
                    case EXTENDS: {
                        Type bound = wildUpperBound(s);
                        undetvar.addBound(InferenceBound.UPPER, bound, this);
                        break;
                    }
                    case SUPER: {
                        Type bound = wildLowerBound(s);
                        undetvar.addBound(InferenceBound.LOWER, bound, this);
                        break;
                    }
                }
                return true;
            } else {
                return isSameType(t, s);
            }
        case ERROR:
            return true;
        default:
            return containsType(s, t);
        }
    }

    boolean containsType(List<Type> ts, List<Type> ss) {
        while (ts.nonEmpty() && ss.nonEmpty()
               && containsType(ts.head, ss.head)) {
            ts = ts.tail;
            ss = ss.tail;
        }
        return ts.isEmpty() && ss.isEmpty();
    }

    
Check if t contains s.
T contains S if:
L(T) <: L(S) && U(S) <: U(T) 
This relation is only used by ClassType.isSubtype(), that
is,
C<S> <: C<T> if T contains S. 
Because of F-bounds, this relation can lead to infinite
recursion.  Thus we must somehow break that recursion.  Notice
that containsType() is only called from ClassType.isSubtype().
Since the arguments have already been checked against their
bounds, we know:
U(S) <: U(T) if T is "super" bound (U(T) *is* the bound) 
L(T) <: L(S) if T is "extends" bound (L(T) is bottom) 
Params:
t – a type
s – a type/**
     * Check if t contains s.
     *
     * <p>T contains S if:
     *
     * <p>{@code L(T) <: L(S) && U(S) <: U(T)}
     *
     * <p>This relation is only used by ClassType.isSubtype(), that
     * is,
     *
     * <p>{@code C<S> <: C<T> if T contains S.}
     *
     * <p>Because of F-bounds, this relation can lead to infinite
     * recursion.  Thus we must somehow break that recursion.  Notice
     * that containsType() is only called from ClassType.isSubtype().
     * Since the arguments have already been checked against their
     * bounds, we know:
     *
     * <p>{@code U(S) <: U(T) if T is "super" bound (U(T) *is* the bound)}
     *
     * <p>{@code L(T) <: L(S) if T is "extends" bound (L(T) is bottom)}
     *
     * @param t a type
     * @param s a type
     */
    public boolean containsType(Type t, Type s) {
        return containsType.visit(t, s);
    }
    // where
        private TypeRelation containsType = new TypeRelation() {

            public Boolean visitType(Type t, Type s) {
                if (s.isPartial())
                    return containedBy(s, t);
                else
                    return isSameType(t, s);
            }

//            void debugContainsType(WildcardType t, Type s) {
//                System.err.println();
//                System.err.format(" does %s contain %s?%n", t, s);
//                System.err.format(" %s U(%s) <: U(%s) %s = %s%n",
//                                  wildUpperBound(s), s, t, wildUpperBound(t),
//                                  t.isSuperBound()
//                                  || isSubtypeNoCapture(wildUpperBound(s), wildUpperBound(t)));
//                System.err.format(" %s L(%s) <: L(%s) %s = %s%n",
//                                  wildLowerBound(t), t, s, wildLowerBound(s),
//                                  t.isExtendsBound()
//                                  || isSubtypeNoCapture(wildLowerBound(t), wildLowerBound(s)));
//                System.err.println();
//            }

            @Override
            public Boolean visitWildcardType(WildcardType t, Type s) {
                if (s.isPartial())
                    return containedBy(s, t);
                else {
//                    debugContainsType(t, s);
                    return isSameWildcard(t, s)
                        || isCaptureOf(s, t)
                        || ((t.isExtendsBound() || isSubtypeNoCapture(wildLowerBound(t), wildLowerBound(s))) &&
                            (t.isSuperBound() || isSubtypeNoCapture(wildUpperBound(s), wildUpperBound(t))));
                }
            }

            @Override
            public Boolean visitUndetVar(UndetVar t, Type s) {
                if (!s.hasTag(WILDCARD)) {
                    return isSameType(t, s);
                } else {
                    return false;
                }
            }

            @Override
            public Boolean visitErrorType(ErrorType t, Type s) {
                return true;
            }
        };

    public boolean isCaptureOf(Type s, WildcardType t) {
        if (!s.hasTag(TYPEVAR) || !((TypeVar)s).isCaptured())
            return false;
        return isSameWildcard(t, ((CapturedType)s).wildcard);
    }

    public boolean isSameWildcard(WildcardType t, Type s) {
        if (!s.hasTag(WILDCARD))
            return false;
        WildcardType w = (WildcardType)s;
        return w.kind == t.kind && w.type == t.type;
    }

    public boolean containsTypeEquivalent(List<Type> ts, List<Type> ss) {
        while (ts.nonEmpty() && ss.nonEmpty()
               && containsTypeEquivalent(ts.head, ss.head)) {
            ts = ts.tail;
            ss = ss.tail;
        }
        return ts.isEmpty() && ss.isEmpty();
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isCastable">
    public boolean isCastable(Type t, Type s) {
        return isCastable(t, s, noWarnings);
    }

    
Is t is castable to s?

s is assumed to be an erased type.

(not defined for Method and ForAll types).
/**
     * Is t is castable to s?<br>
     * s is assumed to be an erased type.<br>
     * (not defined for Method and ForAll types).
     */
    public boolean isCastable(Type t, Type s, Warner warn) {
        if (t == s)
            return true;
        if (t.isPrimitive() != s.isPrimitive()) {
            t = skipTypeVars(t, false);
            return (isConvertible(t, s, warn)
                    || (allowObjectToPrimitiveCast &&
                        s.isPrimitive() &&
                        isSubtype(boxedClass(s).type, t)));
        }
        if (warn != warnStack.head) {
            try {
                warnStack = warnStack.prepend(warn);
                checkUnsafeVarargsConversion(t, s, warn);
                return isCastable.visit(t,s);
            } finally {
                warnStack = warnStack.tail;
            }
        } else {
            return isCastable.visit(t,s);
        }
    }
    // where
        private TypeRelation isCastable = new TypeRelation() {

            public Boolean visitType(Type t, Type s) {
                if (s.hasTag(ERROR))
                    return true;

                switch (t.getTag()) {
                case BYTE: case CHAR: case SHORT: case INT: case LONG: case FLOAT:
                case DOUBLE:
                    return s.isNumeric();
                case BOOLEAN:
                    return s.hasTag(BOOLEAN);
                case VOID:
                    return false;
                case BOT:
                    return isSubtype(t, s);
                default:
                    throw new AssertionError();
                }
            }

            @Override
            public Boolean visitWildcardType(WildcardType t, Type s) {
                return isCastable(wildUpperBound(t), s, warnStack.head);
            }

            @Override
            public Boolean visitClassType(ClassType t, Type s) {
                if (s.hasTag(ERROR) || s.hasTag(BOT))
                    return true;

                if (s.hasTag(TYPEVAR)) {
                    if (isCastable(t, s.getUpperBound(), noWarnings)) {
                        warnStack.head.warn(LintCategory.UNCHECKED);
                        return true;
                    } else {
                        return false;
                    }
                }

                if (t.isCompound() || s.isCompound()) {
                    return !t.isCompound() ?
                            visitCompoundType((ClassType)s, t, true) :
                            visitCompoundType(t, s, false);
                }

                if (s.hasTag(CLASS) || s.hasTag(ARRAY)) {
                    boolean upcast;
                    if ((upcast = isSubtype(erasure(t), erasure(s)))
                        || isSubtype(erasure(s), erasure(t))) {
                        if (!upcast && s.hasTag(ARRAY)) {
                            if (!isReifiable(s))
                                warnStack.head.warn(LintCategory.UNCHECKED);
                            return true;
                        } else if (s.isRaw()) {
                            return true;
                        } else if (t.isRaw()) {
                            if (!isUnbounded(s))
                                warnStack.head.warn(LintCategory.UNCHECKED);
                            return true;
                        }
                        // Assume |a| <: |b|
                        final Type a = upcast ? t : s;
                        final Type b = upcast ? s : t;
                        final boolean HIGH = true;
                        final boolean LOW = false;
                        final boolean DONT_REWRITE_TYPEVARS = false;
                        Type aHigh = rewriteQuantifiers(a, HIGH, DONT_REWRITE_TYPEVARS);
                        Type aLow  = rewriteQuantifiers(a, LOW,  DONT_REWRITE_TYPEVARS);
                        Type bHigh = rewriteQuantifiers(b, HIGH, DONT_REWRITE_TYPEVARS);
                        Type bLow  = rewriteQuantifiers(b, LOW,  DONT_REWRITE_TYPEVARS);
                        Type lowSub = asSub(bLow, aLow.tsym);
                        Type highSub = (lowSub == null) ? null : asSub(bHigh, aHigh.tsym);
                        if (highSub == null) {
                            final boolean REWRITE_TYPEVARS = true;
                            aHigh = rewriteQuantifiers(a, HIGH, REWRITE_TYPEVARS);
                            aLow  = rewriteQuantifiers(a, LOW,  REWRITE_TYPEVARS);
                            bHigh = rewriteQuantifiers(b, HIGH, REWRITE_TYPEVARS);
                            bLow  = rewriteQuantifiers(b, LOW,  REWRITE_TYPEVARS);
                            lowSub = asSub(bLow, aLow.tsym);
                            highSub = (lowSub == null) ? null : asSub(bHigh, aHigh.tsym);
                        }
                        if (highSub != null) {
                            if (!(a.tsym == highSub.tsym && a.tsym == lowSub.tsym)) {
                                Assert.error(a.tsym + " != " + highSub.tsym + " != " + lowSub.tsym);
                            }
                            if (!disjointTypes(aHigh.allparams(), highSub.allparams())
                                && !disjointTypes(aHigh.allparams(), lowSub.allparams())
                                && !disjointTypes(aLow.allparams(), highSub.allparams())
                                && !disjointTypes(aLow.allparams(), lowSub.allparams())) {
                                if (upcast ? giveWarning(a, b) :
                                    giveWarning(b, a))
                                    warnStack.head.warn(LintCategory.UNCHECKED);
                                return true;
                            }
                        }
                        if (isReifiable(s))
                            return isSubtypeUnchecked(a, b);
                        else
                            return isSubtypeUnchecked(a, b, warnStack.head);
                    }

                    // Sidecast
                    if (s.hasTag(CLASS)) {
                        if ((s.tsym.flags() & INTERFACE) != 0) {
                            return ((t.tsym.flags() & FINAL) == 0)
                                ? sideCast(t, s, warnStack.head)
                                : sideCastFinal(t, s, warnStack.head);
                        } else if ((t.tsym.flags() & INTERFACE) != 0) {
                            return ((s.tsym.flags() & FINAL) == 0)
                                ? sideCast(t, s, warnStack.head)
                                : sideCastFinal(t, s, warnStack.head);
                        } else {
                            // unrelated class types
                            return false;
                        }
                    }
                }
                return false;
            }

            boolean visitCompoundType(ClassType ct, Type s, boolean reverse) {
                Warner warn = noWarnings;
                for (Type c : directSupertypes(ct)) {
                    warn.clear();
                    if (reverse ? !isCastable(s, c, warn) : !isCastable(c, s, warn))
                        return false;
                }
                if (warn.hasLint(LintCategory.UNCHECKED))
                    warnStack.head.warn(LintCategory.UNCHECKED);
                return true;
            }

            @Override
            public Boolean visitArrayType(ArrayType t, Type s) {
                switch (s.getTag()) {
                case ERROR:
                case BOT:
                    return true;
                case TYPEVAR:
                    if (isCastable(s, t, noWarnings)) {
                        warnStack.head.warn(LintCategory.UNCHECKED);
                        return true;
                    } else {
                        return false;
                    }
                case CLASS:
                    return isSubtype(t, s);
                case ARRAY:
                    if (elemtype(t).isPrimitive() || elemtype(s).isPrimitive()) {
                        return elemtype(t).hasTag(elemtype(s).getTag());
                    } else {
                        return visit(elemtype(t), elemtype(s));
                    }
                default:
                    return false;
                }
            }

            @Override
            public Boolean visitTypeVar(TypeVar t, Type s) {
                switch (s.getTag()) {
                case ERROR:
                case BOT:
                    return true;
                case TYPEVAR:
                    if (isSubtype(t, s)) {
                        return true;
                    } else if (isCastable(t.getUpperBound(), s, noWarnings)) {
                        warnStack.head.warn(LintCategory.UNCHECKED);
                        return true;
                    } else {
                        return false;
                    }
                default:
                    return isCastable(t.getUpperBound(), s, warnStack.head);
                }
            }

            @Override
            public Boolean visitErrorType(ErrorType t, Type s) {
                return true;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="disjointTypes">
    public boolean disjointTypes(List<Type> ts, List<Type> ss) {
        while (ts.tail != null && ss.tail != null) {
            if (disjointType(ts.head, ss.head)) return true;
            ts = ts.tail;
            ss = ss.tail;
        }
        return false;
    }

    
Two types or wildcards are considered disjoint if it can be proven that no type can be contained in both. It is conservative in that it is allowed to say that two types are not disjoint, even though they actually are. The type C<X> is castable to C<Y> exactly if X and Y are not disjoint. /**
     * Two types or wildcards are considered disjoint if it can be
     * proven that no type can be contained in both. It is
     * conservative in that it is allowed to say that two types are
     * not disjoint, even though they actually are.
     *
     * The type {@code C<X>} is castable to {@code C<Y>} exactly if
     * {@code X} and {@code Y} are not disjoint.
     */
    public boolean disjointType(Type t, Type s) {
        return disjointType.visit(t, s);
    }
    // where
        private TypeRelation disjointType = new TypeRelation() {

            private Set<TypePair> cache = new HashSet<>();

            @Override
            public Boolean visitType(Type t, Type s) {
                if (s.hasTag(WILDCARD))
                    return visit(s, t);
                else
                    return notSoftSubtypeRecursive(t, s) || notSoftSubtypeRecursive(s, t);
            }

            private boolean isCastableRecursive(Type t, Type s) {
                TypePair pair = new TypePair(t, s);
                if (cache.add(pair)) {
                    try {
                        return Types.this.isCastable(t, s);
                    } finally {
                        cache.remove(pair);
                    }
                } else {
                    return true;
                }
            }

            private boolean notSoftSubtypeRecursive(Type t, Type s) {
                TypePair pair = new TypePair(t, s);
                if (cache.add(pair)) {
                    try {
                        return Types.this.notSoftSubtype(t, s);
                    } finally {
                        cache.remove(pair);
                    }
                } else {
                    return false;
                }
            }

            @Override
            public Boolean visitWildcardType(WildcardType t, Type s) {
                if (t.isUnbound())
                    return false;

                if (!s.hasTag(WILDCARD)) {
                    if (t.isExtendsBound())
                        return notSoftSubtypeRecursive(s, t.type);
                    else
                        return notSoftSubtypeRecursive(t.type, s);
                }

                if (s.isUnbound())
                    return false;

                if (t.isExtendsBound()) {
                    if (s.isExtendsBound())
                        return !isCastableRecursive(t.type, wildUpperBound(s));
                    else if (s.isSuperBound())
                        return notSoftSubtypeRecursive(wildLowerBound(s), t.type);
                } else if (t.isSuperBound()) {
                    if (s.isExtendsBound())
                        return notSoftSubtypeRecursive(t.type, wildUpperBound(s));
                }
                return false;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="cvarLowerBounds">
    public List<Type> cvarLowerBounds(List<Type> ts) {
        return ts.map(cvarLowerBoundMapping);
    }
        private final TypeMapping<Void> cvarLowerBoundMapping = new TypeMapping<Void>() {
            @Override
            public Type visitCapturedType(CapturedType t, Void _unused) {
                return cvarLowerBound(t);
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="notSoftSubtype">
    
This relation answers the question: is impossible that something of type `t' can be a subtype of `s'? This is different from the question "is `t' not a subtype of `s'?" when type variables are involved: Integer is not a subtype of T where <T extends Number> but it is not true that Integer cannot possibly be a subtype of T. /**
     * This relation answers the question: is impossible that
     * something of type `t' can be a subtype of `s'? This is
     * different from the question "is `t' not a subtype of `s'?"
     * when type variables are involved: Integer is not a subtype of T
     * where {@code <T extends Number>} but it is not true that Integer cannot
     * possibly be a subtype of T.
     */
    public boolean notSoftSubtype(Type t, Type s) {
        if (t == s) return false;
        if (t.hasTag(TYPEVAR)) {
            TypeVar tv = (TypeVar) t;
            return !isCastable(tv.getUpperBound(),
                               relaxBound(s),
                               noWarnings);
        }
        if (!s.hasTag(WILDCARD))
            s = cvarUpperBound(s);

        return !isSubtype(t, relaxBound(s));
    }

    private Type relaxBound(Type t) {
        return (t.hasTag(TYPEVAR)) ?
                rewriteQuantifiers(skipTypeVars(t, false), true, true) :
                t;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isReifiable">
    public boolean isReifiable(Type t) {
        return isReifiable.visit(t);
    }
    // where
        private UnaryVisitor<Boolean> isReifiable = new UnaryVisitor<Boolean>() {

            public Boolean visitType(Type t, Void ignored) {
                return true;
            }

            @Override
            public Boolean visitClassType(ClassType t, Void ignored) {
                if (t.isCompound())
                    return false;
                else {
                    if (!t.isParameterized())
                        return true;

                    for (Type param : t.allparams()) {
                        if (!param.isUnbound())
                            return false;
                    }
                    return true;
                }
            }

            @Override
            public Boolean visitArrayType(ArrayType t, Void ignored) {
                return visit(t.elemtype);
            }

            @Override
            public Boolean visitTypeVar(TypeVar t, Void ignored) {
                return false;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Array Utils">
    public boolean isArray(Type t) {
        while (t.hasTag(WILDCARD))
            t = wildUpperBound(t);
        return t.hasTag(ARRAY);
    }

    
The element type of an array.
/**
     * The element type of an array.
     */
    public Type elemtype(Type t) {
        switch (t.getTag()) {
        case WILDCARD:
            return elemtype(wildUpperBound(t));
        case ARRAY:
            return ((ArrayType)t).elemtype;
        case FORALL:
            return elemtype(((ForAll)t).qtype);
        case ERROR:
            return t;
        default:
            return null;
        }
    }

    public Type elemtypeOrType(Type t) {
        Type elemtype = elemtype(t);
        return elemtype != null ?
            elemtype :
            t;
    }

    
Mapping to take element type of an arraytype
/**
     * Mapping to take element type of an arraytype
     */
    private TypeMapping<Void> elemTypeFun = new TypeMapping<Void>() {
        @Override
        public Type visitArrayType(ArrayType t, Void _unused) {
            return t.elemtype;
        }

        @Override
        public Type visitTypeVar(TypeVar t, Void _unused) {
            return visit(skipTypeVars(t, false));
        }
    };

    
The number of dimensions of an array type.
/**
     * The number of dimensions of an array type.
     */
    public int dimensions(Type t) {
        int result = 0;
        while (t.hasTag(ARRAY)) {
            result++;
            t = elemtype(t);
        }
        return result;
    }

    
Returns an ArrayType with the component type t
Params:
t – The component type of the ArrayType
Returns:
the ArrayType for the given component/**
     * Returns an ArrayType with the component type t
     *
     * @param t The component type of the ArrayType
     * @return the ArrayType for the given component
     */
    public ArrayType makeArrayType(Type t) {
        if (t.hasTag(VOID) || t.hasTag(PACKAGE)) {
            Assert.error("Type t must not be a VOID or PACKAGE type, " + t.toString());
        }
        return new ArrayType(t, syms.arrayClass);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="asSuper">
    
Return the (most specific) base type of t that starts with the
given symbol.  If none exists, return null.
Caveat Emptor: Since javac represents the class of all arrays with a singleton
symbol Symtab.arrayClass, which by being a singleton cannot hold any discriminant,
this method could yield surprising answers when invoked on arrays. For example when
invoked with t being byte [] and sym being t.sym itself, asSuper would answer null.
Params:
t – a type
sym – a symbol/**
     * Return the (most specific) base type of t that starts with the
     * given symbol.  If none exists, return null.
     *
     * Caveat Emptor: Since javac represents the class of all arrays with a singleton
     * symbol Symtab.arrayClass, which by being a singleton cannot hold any discriminant,
     * this method could yield surprising answers when invoked on arrays. For example when
     * invoked with t being byte [] and sym being t.sym itself, asSuper would answer null.
     *
     * @param t a type
     * @param sym a symbol
     */
    public Type asSuper(Type t, Symbol sym) {
        /* Some examples:
         *
         * (Enum<E>, Comparable) => Comparable<E>
         * (c.s.s.d.AttributeTree.ValueKind, Enum) => Enum<c.s.s.d.AttributeTree.ValueKind>
         * (c.s.s.t.ExpressionTree, c.s.s.t.Tree) => c.s.s.t.Tree
         * (j.u.List<capture#160 of ? extends c.s.s.d.DocTree>, Iterable) =>
         *     Iterable<capture#160 of ? extends c.s.s.d.DocTree>
         */
        if (sym.type == syms.objectType) { //optimization
            return syms.objectType;
        }
        return asSuper.visit(t, sym);
    }
    // where
        private SimpleVisitor<Type,Symbol> asSuper = new SimpleVisitor<Type,Symbol>() {

            public Type visitType(Type t, Symbol sym) {
                return null;
            }

            @Override
            public Type visitClassType(ClassType t, Symbol sym) {
                if (t.tsym == sym)
                    return t;

                Type st = supertype(t);
                if (st.hasTag(CLASS) || st.hasTag(TYPEVAR)) {
                    Type x = asSuper(st, sym);
                    if (x != null)
                        return x;
                }
                if ((sym.flags() & INTERFACE) != 0) {
                    for (List<Type> l = interfaces(t); l.nonEmpty(); l = l.tail) {
                        if (!l.head.hasTag(ERROR)) {
                            Type x = asSuper(l.head, sym);
                            if (x != null)
                                return x;
                        }
                    }
                }
                return null;
            }

            @Override
            public Type visitArrayType(ArrayType t, Symbol sym) {
                return isSubtype(t, sym.type) ? sym.type : null;
            }

            @Override
            public Type visitTypeVar(TypeVar t, Symbol sym) {
                if (t.tsym == sym)
                    return t;
                else
                    return asSuper(t.getUpperBound(), sym);
            }

            @Override
            public Type visitErrorType(ErrorType t, Symbol sym) {
                return t;
            }
        };

    
Return the base type of t or any of its outer types that starts
with the given symbol.  If none exists, return null.
Params:
t – a type
sym – a symbol/**
     * Return the base type of t or any of its outer types that starts
     * with the given symbol.  If none exists, return null.
     *
     * @param t a type
     * @param sym a symbol
     */
    public Type asOuterSuper(Type t, Symbol sym) {
        switch (t.getTag()) {
        case CLASS:
            do {
                Type s = asSuper(t, sym);
                if (s != null) return s;
                t = t.getEnclosingType();
            } while (t.hasTag(CLASS));
            return null;
        case ARRAY:
            return isSubtype(t, sym.type) ? sym.type : null;
        case TYPEVAR:
            return asSuper(t, sym);
        case ERROR:
            return t;
        default:
            return null;
        }
    }

    
Return the base type of t or any of its enclosing types that
starts with the given symbol.  If none exists, return null.
Params:
t – a type
sym – a symbol/**
     * Return the base type of t or any of its enclosing types that
     * starts with the given symbol.  If none exists, return null.
     *
     * @param t a type
     * @param sym a symbol
     */
    public Type asEnclosingSuper(Type t, Symbol sym) {
        switch (t.getTag()) {
        case CLASS:
            do {
                Type s = asSuper(t, sym);
                if (s != null) return s;
                Type outer = t.getEnclosingType();
                t = (outer.hasTag(CLASS)) ? outer :
                    (t.tsym.owner.enclClass() != null) ? t.tsym.owner.enclClass().type :
                    Type.noType;
            } while (t.hasTag(CLASS));
            return null;
        case ARRAY:
            return isSubtype(t, sym.type) ? sym.type : null;
        case TYPEVAR:
            return asSuper(t, sym);
        case ERROR:
            return t;
        default:
            return null;
        }
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="memberType">
    
The type of given symbol, seen as a member of t.
Params:
t – a type
sym – a symbol/**
     * The type of given symbol, seen as a member of t.
     *
     * @param t a type
     * @param sym a symbol
     */
    public Type memberType(Type t, Symbol sym) {
        return (sym.flags() & STATIC) != 0
            ? sym.type
            : memberType.visit(t, sym);
        }
    // where
        private SimpleVisitor<Type,Symbol> memberType = new SimpleVisitor<Type,Symbol>() {

            public Type visitType(Type t, Symbol sym) {
                return sym.type;
            }

            @Override
            public Type visitWildcardType(WildcardType t, Symbol sym) {
                return memberType(wildUpperBound(t), sym);
            }

            @Override
            public Type visitClassType(ClassType t, Symbol sym) {
                Symbol owner = sym.owner;
                long flags = sym.flags();
                if (((flags & STATIC) == 0) && owner.type.isParameterized()) {
                    Type base = asOuterSuper(t, owner);
                    //if t is an intersection type T = CT & I1 & I2 ... & In
                    //its supertypes CT, I1, ... In might contain wildcards
                    //so we need to go through capture conversion
                    base = t.isCompound() ? capture(base) : base;
                    if (base != null) {
                        List<Type> ownerParams = owner.type.allparams();
                        List<Type> baseParams = base.allparams();
                        if (ownerParams.nonEmpty()) {
                            if (baseParams.isEmpty()) {
                                // then base is a raw type
                                return erasure(sym.type);
                            } else {
                                return subst(sym.type, ownerParams, baseParams);
                            }
                        }
                    }
                }
                return sym.type;
            }

            @Override
            public Type visitTypeVar(TypeVar t, Symbol sym) {
                return memberType(t.getUpperBound(), sym);
            }

            @Override
            public Type visitErrorType(ErrorType t, Symbol sym) {
                return t;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isAssignable">
    public boolean isAssignable(Type t, Type s) {
        return isAssignable(t, s, noWarnings);
    }

    
Is t assignable to s?

Equivalent to subtype except for constant values and raw
types.

(not defined for Method and ForAll types)
/**
     * Is t assignable to s?<br>
     * Equivalent to subtype except for constant values and raw
     * types.<br>
     * (not defined for Method and ForAll types)
     */
    public boolean isAssignable(Type t, Type s, Warner warn) {
        if (t.hasTag(ERROR))
            return true;
        if (t.getTag().isSubRangeOf(INT) && t.constValue() != null) {
            int value = ((Number)t.constValue()).intValue();
            switch (s.getTag()) {
            case BYTE:
            case CHAR:
            case SHORT:
            case INT:
                if (s.getTag().checkRange(value))
                    return true;
                break;
            case CLASS:
                switch (unboxedType(s).getTag()) {
                case BYTE:
                case CHAR:
                case SHORT:
                    return isAssignable(t, unboxedType(s), warn);
                }
                break;
            }
        }
        return isConvertible(t, s, warn);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="erasure">
    
The erasure of t |t| -- the type that results when all type parameters in t are deleted. /**
     * The erasure of t {@code |t|} -- the type that results when all
     * type parameters in t are deleted.
     */
    public Type erasure(Type t) {
        return eraseNotNeeded(t) ? t : erasure(t, false);
    }
    //where
    private boolean eraseNotNeeded(Type t) {
        // We don't want to erase primitive types and String type as that
        // operation is idempotent. Also, erasing these could result in loss
        // of information such as constant values attached to such types.
        return (t.isPrimitive()) || (syms.stringType.tsym == t.tsym);
    }

    private Type erasure(Type t, boolean recurse) {
        if (t.isPrimitive()) {
            return t; /* fast special case */
        } else {
            Type out = erasure.visit(t, recurse);
            return out;
        }
    }
    // where
        private TypeMapping<Boolean> erasure = new StructuralTypeMapping<Boolean>() {
            private Type combineMetadata(final Type s,
                                         final Type t) {
                if (t.getMetadata() != TypeMetadata.EMPTY) {
                    switch (s.getKind()) {
                        case OTHER:
                        case UNION:
                        case INTERSECTION:
                        case PACKAGE:
                        case EXECUTABLE:
                        case NONE:
                        case VOID:
                        case ERROR:
                            return s;
                        default: return s.cloneWithMetadata(s.getMetadata().without(Kind.ANNOTATIONS));
                    }
                } else {
                    return s;
                }
            }

            public Type visitType(Type t, Boolean recurse) {
                if (t.isPrimitive())
                    return t; /*fast special case*/
                else {
                    //other cases already handled
                    return combineMetadata(t, t);
                }
            }

            @Override
            public Type visitWildcardType(WildcardType t, Boolean recurse) {
                Type erased = erasure(wildUpperBound(t), recurse);
                return combineMetadata(erased, t);
            }

            @Override
            public Type visitClassType(ClassType t, Boolean recurse) {
                Type erased = t.tsym.erasure(Types.this);
                if (recurse) {
                    erased = new ErasedClassType(erased.getEnclosingType(),erased.tsym,
                            t.getMetadata().without(Kind.ANNOTATIONS));
                    return erased;
                } else {
                    return combineMetadata(erased, t);
                }
            }

            @Override
            public Type visitTypeVar(TypeVar t, Boolean recurse) {
                Type erased = erasure(t.getUpperBound(), recurse);
                return combineMetadata(erased, t);
            }
        };

    public List<Type> erasure(List<Type> ts) {
        return erasure.visit(ts, false);
    }

    public Type erasureRecursive(Type t) {
        return erasure(t, true);
    }

    public List<Type> erasureRecursive(List<Type> ts) {
        return erasure.visit(ts, true);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="makeIntersectionType">
    
Make an intersection type from non-empty list of types. The list should be ordered according to TypeSymbol.precedes(TypeSymbol, Types). Note that this might cause a symbol completion. Hence, this version of makeIntersectionType may not be called during a classfile read. 
Params:
bounds –    the types from which the intersection type is formed/**
     * Make an intersection type from non-empty list of types.  The list should be ordered according to
     * {@link TypeSymbol#precedes(TypeSymbol, Types)}. Note that this might cause a symbol completion.
     * Hence, this version of makeIntersectionType may not be called during a classfile read.
     *
     * @param bounds    the types from which the intersection type is formed
     */
    public IntersectionClassType makeIntersectionType(List<Type> bounds) {
        return makeIntersectionType(bounds, bounds.head.tsym.isInterface());
    }

    
Make an intersection type from non-empty list of types. The list should be ordered according to TypeSymbol.precedes(TypeSymbol, Types). This does not cause symbol completion as an extra parameter indicates as to whether all bounds are interfaces - in which case the supertype is implicitly assumed to be 'Object'. 
Params:
bounds –        the types from which the intersection type is formed
allInterfaces – are all bounds interface types?/**
     * Make an intersection type from non-empty list of types.  The list should be ordered according to
     * {@link TypeSymbol#precedes(TypeSymbol, Types)}. This does not cause symbol completion as
     * an extra parameter indicates as to whether all bounds are interfaces - in which case the
     * supertype is implicitly assumed to be 'Object'.
     *
     * @param bounds        the types from which the intersection type is formed
     * @param allInterfaces are all bounds interface types?
     */
    public IntersectionClassType makeIntersectionType(List<Type> bounds, boolean allInterfaces) {
        Assert.check(bounds.nonEmpty());
        Type firstExplicitBound = bounds.head;
        if (allInterfaces) {
            bounds = bounds.prepend(syms.objectType);
        }
        ClassSymbol bc =
            new ClassSymbol(ABSTRACT|PUBLIC|SYNTHETIC|COMPOUND|ACYCLIC,
                            Type.moreInfo
                                ? names.fromString(bounds.toString())
                                : names.empty,
                            null,
                            syms.noSymbol);
        IntersectionClassType intersectionType = new IntersectionClassType(bounds, bc, allInterfaces);
        bc.type = intersectionType;
        bc.erasure_field = (bounds.head.hasTag(TYPEVAR)) ?
                syms.objectType : // error condition, recover
                erasure(firstExplicitBound);
        bc.members_field = WriteableScope.create(bc);
        return intersectionType;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="supertype">
    public Type supertype(Type t) {
        return supertype.visit(t);
    }
    // where
        private UnaryVisitor<Type> supertype = new UnaryVisitor<Type>() {

            public Type visitType(Type t, Void ignored) {
                // A note on wildcards: there is no good way to
                // determine a supertype for a super bounded wildcard.
                return Type.noType;
            }

            @Override
            public Type visitClassType(ClassType t, Void ignored) {
                if (t.supertype_field == null) {
                    Type supertype = ((ClassSymbol)t.tsym).getSuperclass();
                    // An interface has no superclass; its supertype is Object.
                    if (t.isInterface())
                        supertype = ((ClassType)t.tsym.type).supertype_field;
                    if (t.supertype_field == null) {
                        List<Type> actuals = classBound(t).allparams();
                        List<Type> formals = t.tsym.type.allparams();
                        if (t.hasErasedSupertypes()) {
                            t.supertype_field = erasureRecursive(supertype);
                        } else if (formals.nonEmpty()) {
                            t.supertype_field = subst(supertype, formals, actuals);
                        }
                        else {
                            t.supertype_field = supertype;
                        }
                    }
                }
                return t.supertype_field;
            }

            
The supertype is always a class type. If the type
variable's bounds start with a class type, this is also
the supertype.  Otherwise, the supertype is
java.lang.Object.
/**
             * The supertype is always a class type. If the type
             * variable's bounds start with a class type, this is also
             * the supertype.  Otherwise, the supertype is
             * java.lang.Object.
             */
            @Override
            public Type visitTypeVar(TypeVar t, Void ignored) {
                if (t.getUpperBound().hasTag(TYPEVAR) ||
                    (!t.getUpperBound().isCompound() && !t.getUpperBound().isInterface())) {
                    return t.getUpperBound();
                } else {
                    return supertype(t.getUpperBound());
                }
            }

            @Override
            public Type visitArrayType(ArrayType t, Void ignored) {
                if (t.elemtype.isPrimitive() || isSameType(t.elemtype, syms.objectType))
                    return arraySuperType();
                else
                    return new ArrayType(supertype(t.elemtype), t.tsym);
            }

            @Override
            public Type visitErrorType(ErrorType t, Void ignored) {
                return Type.noType;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="interfaces">
    
Return the interfaces implemented by this class.
/**
     * Return the interfaces implemented by this class.
     */
    public List<Type> interfaces(Type t) {
        return interfaces.visit(t);
    }
    // where
        private UnaryVisitor<List<Type>> interfaces = new UnaryVisitor<List<Type>>() {

            public List<Type> visitType(Type t, Void ignored) {
                return List.nil();
            }

            @Override
            public List<Type> visitClassType(ClassType t, Void ignored) {
                if (t.interfaces_field == null) {
                    List<Type> interfaces = ((ClassSymbol)t.tsym).getInterfaces();
                    if (t.interfaces_field == null) {
                        // If t.interfaces_field is null, then t must
                        // be a parameterized type (not to be confused
                        // with a generic type declaration).
                        // Terminology:
                        //    Parameterized type: List<String>
                        //    Generic type declaration: class List<E> { ... }
                        // So t corresponds to List<String> and
                        // t.tsym.type corresponds to List<E>.
                        // The reason t must be parameterized type is
                        // that completion will happen as a side
                        // effect of calling
                        // ClassSymbol.getInterfaces.  Since
                        // t.interfaces_field is null after
                        // completion, we can assume that t is not the
                        // type of a class/interface declaration.
                        Assert.check(t != t.tsym.type, t);
                        List<Type> actuals = t.allparams();
                        List<Type> formals = t.tsym.type.allparams();
                        if (t.hasErasedSupertypes()) {
                            t.interfaces_field = erasureRecursive(interfaces);
                        } else if (formals.nonEmpty()) {
                            t.interfaces_field = subst(interfaces, formals, actuals);
                        }
                        else {
                            t.interfaces_field = interfaces;
                        }
                    }
                }
                return t.interfaces_field;
            }

            @Override
            public List<Type> visitTypeVar(TypeVar t, Void ignored) {
                if (t.getUpperBound().isCompound())
                    return interfaces(t.getUpperBound());

                if (t.getUpperBound().isInterface())
                    return List.of(t.getUpperBound());

                return List.nil();
            }
        };

    public List<Type> directSupertypes(Type t) {
        return directSupertypes.visit(t);
    }
    // where
        private final UnaryVisitor<List<Type>> directSupertypes = new UnaryVisitor<List<Type>>() {

            public List<Type> visitType(final Type type, final Void ignored) {
                if (!type.isIntersection()) {
                    final Type sup = supertype(type);
                    return (sup == Type.noType || sup == type || sup == null)
                        ? interfaces(type)
                        : interfaces(type).prepend(sup);
                } else {
                    return ((IntersectionClassType)type).getExplicitComponents();
                }
            }
        };

    public boolean isDirectSuperInterface(TypeSymbol isym, TypeSymbol origin) {
        for (Type i2 : interfaces(origin.type)) {
            if (isym == i2.tsym) return true;
        }
        return false;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="isDerivedRaw">
    Map<Type,Boolean> isDerivedRawCache = new HashMap<>();

    public boolean isDerivedRaw(Type t) {
        Boolean result = isDerivedRawCache.get(t);
        if (result == null) {
            result = isDerivedRawInternal(t);
            isDerivedRawCache.put(t, result);
        }
        return result;
    }

    public boolean isDerivedRawInternal(Type t) {
        if (t.isErroneous())
            return false;
        return
            t.isRaw() ||
            supertype(t) != Type.noType && isDerivedRaw(supertype(t)) ||
            isDerivedRaw(interfaces(t));
    }

    public boolean isDerivedRaw(List<Type> ts) {
        List<Type> l = ts;
        while (l.nonEmpty() && !isDerivedRaw(l.head)) l = l.tail;
        return l.nonEmpty();
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="setBounds">
    
Same as setBounds(TypeVar, List<Type>, boolean), except that third parameter is computed directly, as follows: if all all bounds are interface types, the computed supertype is Object,otherwise the supertype is simply left null (in this case, the supertype is assumed to be the head of the bound list passed as second argument). Note that this check might cause a symbol completion. Hence, this version of setBounds may not be called during a classfile read. 
Params:
t –         a type variable
bounds –    the bounds, must be nonempty/**
     * Same as {@link Types#setBounds(TypeVar, List, boolean)}, except that third parameter is computed directly,
     * as follows: if all all bounds are interface types, the computed supertype is Object,otherwise
     * the supertype is simply left null (in this case, the supertype is assumed to be the head of
     * the bound list passed as second argument). Note that this check might cause a symbol completion.
     * Hence, this version of setBounds may not be called during a classfile read.
     *
     * @param t         a type variable
     * @param bounds    the bounds, must be nonempty
     */
    public void setBounds(TypeVar t, List<Type> bounds) {
        setBounds(t, bounds, bounds.head.tsym.isInterface());
    }

    
Set the bounds field of the given type variable to reflect a (possibly multiple) list of bounds.
This does not cause symbol completion as an extra parameter indicates as to whether all bounds
are interfaces - in which case the supertype is implicitly assumed to be 'Object'.
Params:
t –             a type variable
bounds –        the bounds, must be nonempty
allInterfaces – are all bounds interface types?/**
     * Set the bounds field of the given type variable to reflect a (possibly multiple) list of bounds.
     * This does not cause symbol completion as an extra parameter indicates as to whether all bounds
     * are interfaces - in which case the supertype is implicitly assumed to be 'Object'.
     *
     * @param t             a type variable
     * @param bounds        the bounds, must be nonempty
     * @param allInterfaces are all bounds interface types?
     */
    public void setBounds(TypeVar t, List<Type> bounds, boolean allInterfaces) {
        t.setUpperBound( bounds.tail.isEmpty() ?
                bounds.head :
                makeIntersectionType(bounds, allInterfaces) );
        t.rank_field = -1;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="getBounds">
    
Return list of bounds of the given type variable.
/**
     * Return list of bounds of the given type variable.
     */
    public List<Type> getBounds(TypeVar t) {
        if (t.getUpperBound().hasTag(NONE))
            return List.nil();
        else if (t.getUpperBound().isErroneous() || !t.getUpperBound().isCompound())
            return List.of(t.getUpperBound());
        else if ((erasure(t).tsym.flags() & INTERFACE) == 0)
            return interfaces(t).prepend(supertype(t));
        else
            // No superclass was given in bounds.
            // In this case, supertype is Object, erasure is first interface.
            return interfaces(t);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="classBound">
    
If the given type is a (possibly selected) type variable,
return the bounding class of this type, otherwise return the
type itself.
/**
     * If the given type is a (possibly selected) type variable,
     * return the bounding class of this type, otherwise return the
     * type itself.
     */
    public Type classBound(Type t) {
        return classBound.visit(t);
    }
    // where
        private UnaryVisitor<Type> classBound = new UnaryVisitor<Type>() {

            public Type visitType(Type t, Void ignored) {
                return t;
            }

            @Override
            public Type visitClassType(ClassType t, Void ignored) {
                Type outer1 = classBound(t.getEnclosingType());
                if (outer1 != t.getEnclosingType())
                    return new ClassType(outer1, t.getTypeArguments(), t.tsym,
                                         t.getMetadata());
                else
                    return t;
            }

            @Override
            public Type visitTypeVar(TypeVar t, Void ignored) {
                return classBound(supertype(t));
            }

            @Override
            public Type visitErrorType(ErrorType t, Void ignored) {
                return t;
            }
        };
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="sub signature / override equivalence">
    
Returns true iff the first signature is a sub
signature of the other.  This is not an equivalence
relation.
Params:
t – first signature (possibly raw).
s – second signature (could be subjected to erasure).
See Also:
overrideEquivalent(Type t, Type s)
@jls
section 8.4.2.
Returns:
true if t is a sub signature of s./**
     * Returns true iff the first signature is a <em>sub
     * signature</em> of the other.  This is <b>not</b> an equivalence
     * relation.
     *
     * @jls section 8.4.2.
     * @see #overrideEquivalent(Type t, Type s)
     * @param t first signature (possibly raw).
     * @param s second signature (could be subjected to erasure).
     * @return true if t is a sub signature of s.
     */
    public boolean isSubSignature(Type t, Type s) {
        return isSubSignature(t, s, true);
    }

    public boolean isSubSignature(Type t, Type s, boolean strict) {
        return hasSameArgs(t, s, strict) || hasSameArgs(t, erasure(s), strict);
    }

    
Returns true iff these signatures are related by override
equivalence.  This is the natural extension of
isSubSignature to an equivalence relation.
Params:
t – a signature (possible raw, could be subjected to
erasure).
s – a signature (possible raw, could be subjected to
erasure).
See Also:
isSubSignature(Type t, Type s)
@jls
section 8.4.2.
Returns:
true if either argument is a sub signature of the other./**
     * Returns true iff these signatures are related by <em>override
     * equivalence</em>.  This is the natural extension of
     * isSubSignature to an equivalence relation.
     *
     * @jls section 8.4.2.
     * @see #isSubSignature(Type t, Type s)
     * @param t a signature (possible raw, could be subjected to
     * erasure).
     * @param s a signature (possible raw, could be subjected to
     * erasure).
     * @return true if either argument is a sub signature of the other.
     */
    public boolean overrideEquivalent(Type t, Type s) {
        return hasSameArgs(t, s) ||
            hasSameArgs(t, erasure(s)) || hasSameArgs(erasure(t), s);
    }

    public boolean overridesObjectMethod(TypeSymbol origin, Symbol msym) {
        for (Symbol sym : syms.objectType.tsym.members().getSymbolsByName(msym.name)) {
            if (msym.overrides(sym, origin, Types.this, true)) {
                return true;
            }
        }
        return false;
    }

    
This enum defines the strategy for implementing most specific return type check
during the most specific and functional interface checks.
/**
     * This enum defines the strategy for implementing most specific return type check
     * during the most specific and functional interface checks.
     */
    public enum MostSpecificReturnCheck {
        
Return r1 is more specific than r2 if r1 <: r2. Extra care required for (i) handling method type variables (if either method is generic) and (ii) subtyping should be replaced by type-equivalence for primitives. This is essentially an inlined version of Types.resultSubtype(Type, Type, Warner), where the assignability check has been replaced with a strict subtyping check. /**
         * Return r1 is more specific than r2 if {@code r1 <: r2}. Extra care required for (i) handling
         * method type variables (if either method is generic) and (ii) subtyping should be replaced
         * by type-equivalence for primitives. This is essentially an inlined version of
         * {@link Types#resultSubtype(Type, Type, Warner)}, where the assignability check has been
         * replaced with a strict subtyping check.
         */
        BASIC() {
            @Override
            public boolean test(Type mt1, Type mt2, Types types) {
                List<Type> tvars = mt1.getTypeArguments();
                List<Type> svars = mt2.getTypeArguments();
                Type t = mt1.getReturnType();
                Type s = types.subst(mt2.getReturnType(), svars, tvars);
                return types.isSameType(t, s) ||
                    !t.isPrimitive() &&
                    !s.isPrimitive() &&
                    types.isSubtype(t, s);
            }
        },
        
Return r1 is more specific than r2 if r1 is return-type-substitutable for r2.
/**
         * Return r1 is more specific than r2 if r1 is return-type-substitutable for r2.
         */
        RTS() {
            @Override
            public boolean test(Type mt1, Type mt2, Types types) {
                return types.returnTypeSubstitutable(mt1, mt2);
            }
        };

        public abstract boolean test(Type mt1, Type mt2, Types types);
    }

    
Merge multiple abstract methods. The preferred method is a method that is a subsignature
of all the other signatures and whose return type is more specific {@see MostSpecificReturnCheck}.
The resulting preferred method has a thrown clause that is the intersection of the merged
methods' clauses.
/**
     * Merge multiple abstract methods. The preferred method is a method that is a subsignature
     * of all the other signatures and whose return type is more specific {@see MostSpecificReturnCheck}.
     * The resulting preferred method has a thrown clause that is the intersection of the merged
     * methods' clauses.
     */
    public Optional<Symbol> mergeAbstracts(List<Symbol> ambiguousInOrder, Type site, boolean sigCheck) {
        //first check for preconditions
        boolean shouldErase = false;
        List<Type> erasedParams = ambiguousInOrder.head.erasure(this).getParameterTypes();
        for (Symbol s : ambiguousInOrder) {
            if ((s.flags() & ABSTRACT) == 0 ||
                    (sigCheck && !isSameTypes(erasedParams, s.erasure(this).getParameterTypes()))) {
                return Optional.empty();
            } else if (s.type.hasTag(FORALL)) {
                shouldErase = true;
            }
        }
        //then merge abstracts
        for (MostSpecificReturnCheck mostSpecificReturnCheck : MostSpecificReturnCheck.values()) {
            outer: for (Symbol s : ambiguousInOrder) {
                Type mt = memberType(site, s);
                List<Type> allThrown = mt.getThrownTypes();
                for (Symbol s2 : ambiguousInOrder) {
                    if (s != s2) {
                        Type mt2 = memberType(site, s2);
                        if (!isSubSignature(mt, mt2) ||
                                !mostSpecificReturnCheck.test(mt, mt2, this)) {
                            //ambiguity cannot be resolved
                            continue outer;
                        } else {
                            List<Type> thrownTypes2 = mt2.getThrownTypes();
                            if (!mt.hasTag(FORALL) && shouldErase) {
                                thrownTypes2 = erasure(thrownTypes2);
                            } else if (mt.hasTag(FORALL)) {
                                //subsignature implies that if most specific is generic, then all other
                                //methods are too
                                Assert.check(mt2.hasTag(FORALL));
                                // if both are generic methods, adjust thrown types ahead of intersection computation
                                thrownTypes2 = subst(thrownTypes2, mt2.getTypeArguments(), mt.getTypeArguments());
                            }
                            allThrown = chk.intersect(allThrown, thrownTypes2);
                        }
                    }
                }
                return (allThrown == mt.getThrownTypes()) ?
                        Optional.of(s) :
                        Optional.of(new MethodSymbol(
                                s.flags(),
                                s.name,
                                createMethodTypeWithThrown(s.type, allThrown),
                                s.owner) {
                            @Override
                            public Symbol baseSymbol() {
                                return s;
                            }
                        });
            }
        }
        return Optional.empty();
    }

    // <editor-fold defaultstate="collapsed" desc="Determining method implementation in given site">
    class ImplementationCache {

        private WeakHashMap<MethodSymbol, SoftReference<Map<TypeSymbol, Entry>>> _map = new WeakHashMap<>();

        class Entry {
            final MethodSymbol cachedImpl;
            final Filter<Symbol> implFilter;
            final boolean checkResult;
            final int prevMark;

            public Entry(MethodSymbol cachedImpl,
                    Filter<Symbol> scopeFilter,
                    boolean checkResult,
                    int prevMark) {
                this.cachedImpl = cachedImpl;
                this.implFilter = scopeFilter;
                this.checkResult = checkResult;
                this.prevMark = prevMark;
            }

            boolean matches(Filter<Symbol> scopeFilter, boolean checkResult, int mark) {
                return this.implFilter == scopeFilter &&
                        this.checkResult == checkResult &&
                        this.prevMark == mark;
            }
        }

        MethodSymbol get(MethodSymbol ms, TypeSymbol origin, boolean checkResult, Filter<Symbol> implFilter) {
            SoftReference<Map<TypeSymbol, Entry>> ref_cache = _map.get(ms);
            Map<TypeSymbol, Entry> cache = ref_cache != null ? ref_cache.get() : null;
            if (cache == null) {
                cache = new HashMap<>();
                _map.put(ms, new SoftReference<>(cache));
            }
            Entry e = cache.get(origin);
            CompoundScope members = membersClosure(origin.type, true);
            if (e == null ||
                    !e.matches(implFilter, checkResult, members.getMark())) {
                MethodSymbol impl = implementationInternal(ms, origin, checkResult, implFilter);
                cache.put(origin, new Entry(impl, implFilter, checkResult, members.getMark()));
                return impl;
            }
            else {
                return e.cachedImpl;
            }
        }

        private MethodSymbol implementationInternal(MethodSymbol ms, TypeSymbol origin, boolean checkResult, Filter<Symbol> implFilter) {
            for (Type t = origin.type; t.hasTag(CLASS) || t.hasTag(TYPEVAR); t = supertype(t)) {
                t = skipTypeVars(t, false);
                TypeSymbol c = t.tsym;
                Symbol bestSoFar = null;
                for (Symbol sym : c.members().getSymbolsByName(ms.name, implFilter)) {
                    if (sym != null && sym.overrides(ms, origin, Types.this, checkResult)) {
                        bestSoFar = sym;
                        if ((sym.flags() & ABSTRACT) == 0) {
                            //if concrete impl is found, exit immediately
                            break;
                        }
                    }
                }
                if (bestSoFar != null) {
                    //return either the (only) concrete implementation or the first abstract one
                    return (MethodSymbol)bestSoFar;
                }
            }
            return null;
        }
    }

    private ImplementationCache implCache = new ImplementationCache();

    public MethodSymbol implementation(MethodSymbol ms, TypeSymbol origin, boolean checkResult, Filter<Symbol> implFilter) {
        return implCache.get(ms, origin, checkResult, implFilter);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="compute transitive closure of all members in given site">
    class MembersClosureCache extends SimpleVisitor<Scope.CompoundScope, Void> {

        private Map<TypeSymbol, CompoundScope> _map = new HashMap<>();

        Set<TypeSymbol> seenTypes = new HashSet<>();

        class MembersScope extends CompoundScope {

            CompoundScope scope;

            public MembersScope(CompoundScope scope) {
                super(scope.owner);
                this.scope = scope;
            }

            Filter<Symbol> combine(Filter<Symbol> sf) {
                return s -> !s.owner.isInterface() && (sf == null || sf.accepts(s));
            }

            @Override
            public Iterable<Symbol> getSymbols(Filter<Symbol> sf, LookupKind lookupKind) {
                return scope.getSymbols(combine(sf), lookupKind);
            }

            @Override
            public Iterable<Symbol> getSymbolsByName(Name name, Filter<Symbol> sf, LookupKind lookupKind) {
                return scope.getSymbolsByName(name, combine(sf), lookupKind);
            }

            @Override
            public int getMark() {
                return scope.getMark();
            }
        }

        CompoundScope nilScope;

        
members closure visitor methods /** members closure visitor methods **/

        public CompoundScope visitType(Type t, Void _unused) {
            if (nilScope == null) {
                nilScope = new CompoundScope(syms.noSymbol);
            }
            return nilScope;
        }

        @Override
        public CompoundScope visitClassType(ClassType t, Void _unused) {
            if (!seenTypes.add(t.tsym)) {
                //this is possible when an interface is implemented in multiple
                //superclasses, or when a class hierarchy is circular - in such
                //cases we don't need to recurse (empty scope is returned)
                return new CompoundScope(t.tsym);
            }
            try {
                seenTypes.add(t.tsym);
                ClassSymbol csym = (ClassSymbol)t.tsym;
                CompoundScope membersClosure = _map.get(csym);
                if (membersClosure == null) {
                    membersClosure = new CompoundScope(csym);
                    for (Type i : interfaces(t)) {
                        membersClosure.prependSubScope(visit(i, null));
                    }
                    membersClosure.prependSubScope(visit(supertype(t), null));
                    membersClosure.prependSubScope(csym.members());
                    _map.put(csym, membersClosure);
                }
                return membersClosure;
            }
            finally {
                seenTypes.remove(t.tsym);
            }
        }

        @Override
        public CompoundScope visitTypeVar(TypeVar t, Void _unused) {
            return visit(t.getUpperBound(), null);
        }
    }

    private MembersClosureCache membersCache = new MembersClosureCache();

    public CompoundScope membersClosure(Type site, boolean skipInterface) {
        CompoundScope cs = membersCache.visit(site, null);
        Assert.checkNonNull(cs, () -> "type " + site);
        return skipInterface ? membersCache.new MembersScope(cs) : cs;
    }
    // </editor-fold>


    
Return first abstract member of class `sym'.
/** Return first abstract member of class `sym'.
     */
    public MethodSymbol firstUnimplementedAbstract(ClassSymbol sym) {
        try {
            return firstUnimplementedAbstractImpl(sym, sym);
        } catch (CompletionFailure ex) {
            chk.completionError(enter.getEnv(sym).tree.pos(), ex);
            return null;
        }
    }
        //where:
        private MethodSymbol firstUnimplementedAbstractImpl(ClassSymbol impl, ClassSymbol c) {
            MethodSymbol undef = null;
            // Do not bother to search in classes that are not abstract,
            // since they cannot have abstract members.
            if (c == impl || (c.flags() & (ABSTRACT | INTERFACE)) != 0) {
                Scope s = c.members();
                for (Symbol sym : s.getSymbols(NON_RECURSIVE)) {
                    if (sym.kind == MTH &&
                        (sym.flags() & (ABSTRACT|DEFAULT|PRIVATE)) == ABSTRACT) {
                        MethodSymbol absmeth = (MethodSymbol)sym;
                        MethodSymbol implmeth = absmeth.implementation(impl, this, true);
                        if (implmeth == null || implmeth == absmeth) {
                            //look for default implementations
                            if (allowDefaultMethods) {
                                MethodSymbol prov = interfaceCandidates(impl.type, absmeth).head;
                                if (prov != null && prov.overrides(absmeth, impl, this, true)) {
                                    implmeth = prov;
                                }
                            }
                        }
                        if (implmeth == null || implmeth == absmeth) {
                            undef = absmeth;
                            break;
                        }
                    }
                }
                if (undef == null) {
                    Type st = supertype(c.type);
                    if (st.hasTag(CLASS))
                        undef = firstUnimplementedAbstractImpl(impl, (ClassSymbol)st.tsym);
                }
                for (List<Type> l = interfaces(c.type);
                     undef == null && l.nonEmpty();
                     l = l.tail) {
                    undef = firstUnimplementedAbstractImpl(impl, (ClassSymbol)l.head.tsym);
                }
            }
            return undef;
        }

    public class CandidatesCache {
        public Map<Entry, List<MethodSymbol>> cache = new WeakHashMap<>();

        class Entry {
            Type site;
            MethodSymbol msym;

            Entry(Type site, MethodSymbol msym) {
                this.site = site;
                this.msym = msym;
            }

            @Override
            public boolean equals(Object obj) {
                if (obj instanceof Entry) {
                    Entry e = (Entry)obj;
                    return e.msym == msym && isSameType(site, e.site);
                } else {
                    return false;
                }
            }

            @Override
            public int hashCode() {
                return Types.this.hashCode(site) & ~msym.hashCode();
            }
        }

        public List<MethodSymbol> get(Entry e) {
            return cache.get(e);
        }

        public void put(Entry e, List<MethodSymbol> msymbols) {
            cache.put(e, msymbols);
        }
    }

    public CandidatesCache candidatesCache = new CandidatesCache();

    //where
    public List<MethodSymbol> interfaceCandidates(Type site, MethodSymbol ms) {
        CandidatesCache.Entry e = candidatesCache.new Entry(site, ms);
        List<MethodSymbol> candidates = candidatesCache.get(e);
        if (candidates == null) {
            Filter<Symbol> filter = new MethodFilter(ms, site);
            List<MethodSymbol> candidates2 = List.nil();
            for (Symbol s : membersClosure(site, false).getSymbols(filter)) {
                if (!site.tsym.isInterface() && !s.owner.isInterface()) {
                    return List.of((MethodSymbol)s);
                } else if (!candidates2.contains(s)) {
                    candidates2 = candidates2.prepend((MethodSymbol)s);
                }
            }
            candidates = prune(candidates2);
            candidatesCache.put(e, candidates);
        }
        return candidates;
    }

    public List<MethodSymbol> prune(List<MethodSymbol> methods) {
        ListBuffer<MethodSymbol> methodsMin = new ListBuffer<>();
        for (MethodSymbol m1 : methods) {
            boolean isMin_m1 = true;
            for (MethodSymbol m2 : methods) {
                if (m1 == m2) continue;
                if (m2.owner != m1.owner &&
                        asSuper(m2.owner.type, m1.owner) != null) {
                    isMin_m1 = false;
                    break;
                }
            }
            if (isMin_m1)
                methodsMin.append(m1);
        }
        return methodsMin.toList();
    }
    // where
            private class MethodFilter implements Filter<Symbol> {

                Symbol msym;
                Type site;

                MethodFilter(Symbol msym, Type site) {
                    this.msym = msym;
                    this.site = site;
                }

                public boolean accepts(Symbol s) {
                    return s.kind == MTH &&
                            s.name == msym.name &&
                            (s.flags() & SYNTHETIC) == 0 &&
                            s.isInheritedIn(site.tsym, Types.this) &&
                            overrideEquivalent(memberType(site, s), memberType(site, msym));
                }
            }
    // </editor-fold>

    
Does t have the same arguments as s?  It is assumed that both
types are (possibly polymorphic) method types.  Monomorphic
method types "have the same arguments", if their argument lists
are equal.  Polymorphic method types "have the same arguments",
if they have the same arguments after renaming all type
variables of one to corresponding type variables in the other,
where correspondence is by position in the type parameter list.
/**
     * Does t have the same arguments as s?  It is assumed that both
     * types are (possibly polymorphic) method types.  Monomorphic
     * method types "have the same arguments", if their argument lists
     * are equal.  Polymorphic method types "have the same arguments",
     * if they have the same arguments after renaming all type
     * variables of one to corresponding type variables in the other,
     * where correspondence is by position in the type parameter list.
     */
    public boolean hasSameArgs(Type t, Type s) {
        return hasSameArgs(t, s, true);
    }

    public boolean hasSameArgs(Type t, Type s, boolean strict) {
        return hasSameArgs(t, s, strict ? hasSameArgs_strict : hasSameArgs_nonstrict);
    }

    private boolean hasSameArgs(Type t, Type s, TypeRelation hasSameArgs) {
        return hasSameArgs.visit(t, s);
    }
    // where
        private class HasSameArgs extends TypeRelation {

            boolean strict;

            public HasSameArgs(boolean strict) {
                this.strict = strict;
            }

            public Boolean visitType(Type t, Type s) {
                throw new AssertionError();
            }

            @Override
            public Boolean visitMethodType(MethodType t, Type s) {
                return s.hasTag(METHOD)
                    && containsTypeEquivalent(t.argtypes, s.getParameterTypes());
            }

            @Override
            public Boolean visitForAll(ForAll t, Type s) {
                if (!s.hasTag(FORALL))
                    return strict ? false : visitMethodType(t.asMethodType(), s);

                ForAll forAll = (ForAll)s;
                return hasSameBounds(t, forAll)
                    && visit(t.qtype, subst(forAll.qtype, forAll.tvars, t.tvars));
            }

            @Override
            public Boolean visitErrorType(ErrorType t, Type s) {
                return false;
            }
        }

    TypeRelation hasSameArgs_strict = new HasSameArgs(true);
        TypeRelation hasSameArgs_nonstrict = new HasSameArgs(false);

    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="subst">
    public List<Type> subst(List<Type> ts,
                            List<Type> from,
                            List<Type> to) {
        return ts.map(new Subst(from, to));
    }

    
Substitute all occurrences of a type in `from' with the
corresponding type in `to' in 't'. Match lists `from' and `to'
from the right: If lists have different length, discard leading
elements of the longer list.
/**
     * Substitute all occurrences of a type in `from' with the
     * corresponding type in `to' in 't'. Match lists `from' and `to'
     * from the right: If lists have different length, discard leading
     * elements of the longer list.
     */
    public Type subst(Type t, List<Type> from, List<Type> to) {
        return t.map(new Subst(from, to));
    }

    private class Subst extends StructuralTypeMapping<Void> {
        List<Type> from;
        List<Type> to;

        public Subst(List<Type> from, List<Type> to) {
            int fromLength = from.length();
            int toLength = to.length();
            while (fromLength > toLength) {
                fromLength--;
                from = from.tail;
            }
            while (fromLength < toLength) {
                toLength--;
                to = to.tail;
            }
            this.from = from;
            this.to = to;
        }

        @Override
        public Type visitTypeVar(TypeVar t, Void ignored) {
            for (List<Type> from = this.from, to = this.to;
                 from.nonEmpty();
                 from = from.tail, to = to.tail) {
                if (t.equalsIgnoreMetadata(from.head)) {
                    return to.head.withTypeVar(t);
                }
            }
            return t;
        }

        @Override
        public Type visitClassType(ClassType t, Void ignored) {
            if (!t.isCompound()) {
                return super.visitClassType(t, ignored);
            } else {
                Type st = visit(supertype(t));
                List<Type> is = visit(interfaces(t), ignored);
                if (st == supertype(t) && is == interfaces(t))
                    return t;
                else
                    return makeIntersectionType(is.prepend(st));
            }
        }

        @Override
        public Type visitWildcardType(WildcardType t, Void ignored) {
            WildcardType t2 = (WildcardType)super.visitWildcardType(t, ignored);
            if (t2 != t && t.isExtendsBound() && t2.type.isExtendsBound()) {
                t2.type = wildUpperBound(t2.type);
            }
            return t2;
        }

        @Override
        public Type visitForAll(ForAll t, Void ignored) {
            if (Type.containsAny(to, t.tvars)) {
                //perform alpha-renaming of free-variables in 't'
                //if 'to' types contain variables that are free in 't'
                List<Type> freevars = newInstances(t.tvars);
                t = new ForAll(freevars,
                               Types.this.subst(t.qtype, t.tvars, freevars));
            }
            List<Type> tvars1 = substBounds(t.tvars, from, to);
            Type qtype1 = visit(t.qtype);
            if (tvars1 == t.tvars && qtype1 == t.qtype) {
                return t;
            } else if (tvars1 == t.tvars) {
                return new ForAll(tvars1, qtype1) {
                    @Override
                    public boolean needsStripping() {
                        return true;
                    }
                };
            } else {
                return new ForAll(tvars1, Types.this.subst(qtype1, t.tvars, tvars1)) {
                    @Override
                    public boolean needsStripping() {
                        return true;
                    }
                };
            }
        }
    }

    public List<Type> substBounds(List<Type> tvars,
                                  List<Type> from,
                                  List<Type> to) {
        if (tvars.isEmpty())
            return tvars;
        ListBuffer<Type> newBoundsBuf = new ListBuffer<>();
        boolean changed = false;
        // calculate new bounds
        for (Type t : tvars) {
            TypeVar tv = (TypeVar) t;
            Type bound = subst(tv.getUpperBound(), from, to);
            if (bound != tv.getUpperBound())
                changed = true;
            newBoundsBuf.append(bound);
        }
        if (!changed)
            return tvars;
        ListBuffer<Type> newTvars = new ListBuffer<>();
        // create new type variables without bounds
        for (Type t : tvars) {
            newTvars.append(new TypeVar(t.tsym, null, syms.botType,
                                        t.getMetadata()));
        }
        // the new bounds should use the new type variables in place
        // of the old
        List<Type> newBounds = newBoundsBuf.toList();
        from = tvars;
        to = newTvars.toList();
        for (; !newBounds.isEmpty(); newBounds = newBounds.tail) {
            newBounds.head = subst(newBounds.head, from, to);
        }
        newBounds = newBoundsBuf.toList();
        // set the bounds of new type variables to the new bounds
        for (Type t : newTvars.toList()) {
            TypeVar tv = (TypeVar) t;
            tv.setUpperBound( newBounds.head );
            newBounds = newBounds.tail;
        }
        return newTvars.toList();
    }

    public TypeVar substBound(TypeVar t, List<Type> from, List<Type> to) {
        Type bound1 = subst(t.getUpperBound(), from, to);
        if (bound1 == t.getUpperBound())
            return t;
        else {
            // create new type variable without bounds
            TypeVar tv = new TypeVar(t.tsym, null, syms.botType,
                                     t.getMetadata());
            // the new bound should use the new type variable in place
            // of the old
            tv.setUpperBound( subst(bound1, List.of(t), List.of(tv)) );
            return tv;
        }
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="hasSameBounds">
    
Does t have the same bounds for quantified variables as s?
/**
     * Does t have the same bounds for quantified variables as s?
     */
    public boolean hasSameBounds(ForAll t, ForAll s) {
        List<Type> l1 = t.tvars;
        List<Type> l2 = s.tvars;
        while (l1.nonEmpty() && l2.nonEmpty() &&
               isSameType(l1.head.getUpperBound(),
                          subst(l2.head.getUpperBound(),
                                s.tvars,
                                t.tvars))) {
            l1 = l1.tail;
            l2 = l2.tail;
        }
        return l1.isEmpty() && l2.isEmpty();
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="newInstances">
    
Create new vector of type variables from list of variables
 changing all recursive bounds from old to new list.
/** Create new vector of type variables from list of variables
     *  changing all recursive bounds from old to new list.
     */
    public List<Type> newInstances(List<Type> tvars) {
        List<Type> tvars1 = tvars.map(newInstanceFun);
        for (List<Type> l = tvars1; l.nonEmpty(); l = l.tail) {
            TypeVar tv = (TypeVar) l.head;
            tv.setUpperBound( subst(tv.getUpperBound(), tvars, tvars1) );
        }
        return tvars1;
    }
        private static final TypeMapping<Void> newInstanceFun = new TypeMapping<Void>() {
            @Override
            public TypeVar visitTypeVar(TypeVar t, Void _unused) {
                return new TypeVar(t.tsym, t.getUpperBound(), t.getLowerBound(), t.getMetadata());
            }
        };
    // </editor-fold>

    public Type createMethodTypeWithParameters(Type original, List<Type> newParams) {
        return original.accept(methodWithParameters, newParams);
    }
    // where
        private final MapVisitor<List<Type>> methodWithParameters = new MapVisitor<List<Type>>() {
            public Type visitType(Type t, List<Type> newParams) {
                throw new IllegalArgumentException("Not a method type: " + t);
            }
            public Type visitMethodType(MethodType t, List<Type> newParams) {
                return new MethodType(newParams, t.restype, t.thrown, t.tsym);
            }
            public Type visitForAll(ForAll t, List<Type> newParams) {
                return new ForAll(t.tvars, t.qtype.accept(this, newParams));
            }
        };

    public Type createMethodTypeWithThrown(Type original, List<Type> newThrown) {
        return original.accept(methodWithThrown, newThrown);
    }
    // where
        private final MapVisitor<List<Type>> methodWithThrown = new MapVisitor<List<Type>>() {
            public Type visitType(Type t, List<Type> newThrown) {
                throw new IllegalArgumentException("Not a method type: " + t);
            }
            public Type visitMethodType(MethodType t, List<Type> newThrown) {
                return new MethodType(t.argtypes, t.restype, newThrown, t.tsym);
            }
            public Type visitForAll(ForAll t, List<Type> newThrown) {
                return new ForAll(t.tvars, t.qtype.accept(this, newThrown));
            }
        };

    public Type createMethodTypeWithReturn(Type original, Type newReturn) {
        return original.accept(methodWithReturn, newReturn);
    }
    // where
        private final MapVisitor<Type> methodWithReturn = new MapVisitor<Type>() {
            public Type visitType(Type t, Type newReturn) {
                throw new IllegalArgumentException("Not a method type: " + t);
            }
            public Type visitMethodType(MethodType t, Type newReturn) {
                return new MethodType(t.argtypes, newReturn, t.thrown, t.tsym) {
                    @Override
                    public Type baseType() {
                        return t;
                    }
                };
            }
            public Type visitForAll(ForAll t, Type newReturn) {
                return new ForAll(t.tvars, t.qtype.accept(this, newReturn)) {
                    @Override
                    public Type baseType() {
                        return t;
                    }
                };
            }
        };

    // <editor-fold defaultstate="collapsed" desc="createErrorType">
    public Type createErrorType(Type originalType) {
        return new ErrorType(originalType, syms.errSymbol);
    }

    public Type createErrorType(ClassSymbol c, Type originalType) {
        return new ErrorType(c, originalType);
    }

    public Type createErrorType(Name name, TypeSymbol container, Type originalType) {
        return new ErrorType(name, container, originalType);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="rank">
    
The rank of a class is the length of the longest path between
the class and java.lang.Object in the class inheritance
graph. Undefined for all but reference types.
/**
     * The rank of a class is the length of the longest path between
     * the class and java.lang.Object in the class inheritance
     * graph. Undefined for all but reference types.
     */
    public int rank(Type t) {
        switch(t.getTag()) {
        case CLASS: {
            ClassType cls = (ClassType)t;
            if (cls.rank_field < 0) {
                Name fullname = cls.tsym.getQualifiedName();
                if (fullname == names.java_lang_Object)
                    cls.rank_field = 0;
                else {
                    int r = rank(supertype(cls));
                    for (List<Type> l = interfaces(cls);
                         l.nonEmpty();
                         l = l.tail) {
                        if (rank(l.head) > r)
                            r = rank(l.head);
                    }
                    cls.rank_field = r + 1;
                }
            }
            return cls.rank_field;
        }
        case TYPEVAR: {
            TypeVar tvar = (TypeVar)t;
            if (tvar.rank_field < 0) {
                int r = rank(supertype(tvar));
                for (List<Type> l = interfaces(tvar);
                     l.nonEmpty();
                     l = l.tail) {
                    if (rank(l.head) > r) r = rank(l.head);
                }
                tvar.rank_field = r + 1;
            }
            return tvar.rank_field;
        }
        case ERROR:
        case NONE:
            return 0;
        default:
            throw new AssertionError();
        }
    }
    // </editor-fold>

    
Helper method for generating a string representation of a given type
accordingly to a given locale
/**
     * Helper method for generating a string representation of a given type
     * accordingly to a given locale
     */
    public String toString(Type t, Locale locale) {
        return Printer.createStandardPrinter(messages).visit(t, locale);
    }

    
Helper method for generating a string representation of a given type
accordingly to a given locale
/**
     * Helper method for generating a string representation of a given type
     * accordingly to a given locale
     */
    public String toString(Symbol t, Locale locale) {
        return Printer.createStandardPrinter(messages).visit(t, locale);
    }

    // <editor-fold defaultstate="collapsed" desc="toString">
    
This toString is slightly more descriptive than the one on Type.
Deprecated:
Types.toString(Type t, Locale l) provides better support
for localization/**
     * This toString is slightly more descriptive than the one on Type.
     *
     * @deprecated Types.toString(Type t, Locale l) provides better support
     * for localization
     */
    @Deprecated
    public String toString(Type t) {
        if (t.hasTag(FORALL)) {
            ForAll forAll = (ForAll)t;
            return typaramsString(forAll.tvars) + forAll.qtype;
        }
        return "" + t;
    }
    // where
        private String typaramsString(List<Type> tvars) {
            StringBuilder s = new StringBuilder();
            s.append('<');
            boolean first = true;
            for (Type t : tvars) {
                if (!first) s.append(", ");
                first = false;
                appendTyparamString(((TypeVar)t), s);
            }
            s.append('>');
            return s.toString();
        }
        private void appendTyparamString(TypeVar t, StringBuilder buf) {
            buf.append(t);
            if (t.getUpperBound() == null ||
                t.getUpperBound().tsym.getQualifiedName() == names.java_lang_Object)
                return;
            buf.append(" extends "); // Java syntax; no need for i18n
            Type bound = t.getUpperBound();
            if (!bound.isCompound()) {
                buf.append(bound);
            } else if ((erasure(t).tsym.flags() & INTERFACE) == 0) {
                buf.append(supertype(t));
                for (Type intf : interfaces(t)) {
                    buf.append('&');
                    buf.append(intf);
                }
            } else {
                // No superclass was given in bounds.
                // In this case, supertype is Object, erasure is first interface.
                boolean first = true;
                for (Type intf : interfaces(t)) {
                    if (!first) buf.append('&');
                    first = false;
                    buf.append(intf);
                }
            }
        }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Determining least upper bounds of types">
    
A cache for closures.
A closure is a list of all the supertypes and interfaces of
a class or interface type, ordered by ClassSymbol.precedes
(that is, subclasses come first, arbitrary but fixed
otherwise).
/**
     * A cache for closures.
     *
     * <p>A closure is a list of all the supertypes and interfaces of
     * a class or interface type, ordered by ClassSymbol.precedes
     * (that is, subclasses come first, arbitrary but fixed
     * otherwise).
     */
    private Map<Type,List<Type>> closureCache = new HashMap<>();

    
Returns the closure of a class or interface type.
/**
     * Returns the closure of a class or interface type.
     */
    public List<Type> closure(Type t) {
        List<Type> cl = closureCache.get(t);
        if (cl == null) {
            Type st = supertype(t);
            if (!t.isCompound()) {
                if (st.hasTag(CLASS)) {
                    cl = insert(closure(st), t);
                } else if (st.hasTag(TYPEVAR)) {
                    cl = closure(st).prepend(t);
                } else {
                    cl = List.of(t);
                }
            } else {
                cl = closure(supertype(t));
            }
            for (List<Type> l = interfaces(t); l.nonEmpty(); l = l.tail)
                cl = union(cl, closure(l.head));
            closureCache.put(t, cl);
        }
        return cl;
    }

    
Collect types into a new closure (using a @code{ClosureHolder})
/**
     * Collect types into a new closure (using a @code{ClosureHolder})
     */
    public Collector<Type, ClosureHolder, List<Type>> closureCollector(boolean minClosure, BiPredicate<Type, Type> shouldSkip) {
        return Collector.of(() -> new ClosureHolder(minClosure, shouldSkip),
                ClosureHolder::add,
                ClosureHolder::merge,
                ClosureHolder::closure);
    }
    //where
        class ClosureHolder {
            List<Type> closure;
            final boolean minClosure;
            final BiPredicate<Type, Type> shouldSkip;

            ClosureHolder(boolean minClosure, BiPredicate<Type, Type> shouldSkip) {
                this.closure = List.nil();
                this.minClosure = minClosure;
                this.shouldSkip = shouldSkip;
            }

            void add(Type type) {
                closure = insert(closure, type, shouldSkip);
            }

            ClosureHolder merge(ClosureHolder other) {
                closure = union(closure, other.closure, shouldSkip);
                return this;
            }

            List<Type> closure() {
                return minClosure ? closureMin(closure) : closure;
            }
        }

    BiPredicate<Type, Type> basicClosureSkip = (t1, t2) -> t1.tsym == t2.tsym;

    
Insert a type in a closure
/**
     * Insert a type in a closure
     */
    public List<Type> insert(List<Type> cl, Type t, BiPredicate<Type, Type> shouldSkip) {
        if (cl.isEmpty()) {
            return cl.prepend(t);
        } else if (shouldSkip.test(t, cl.head)) {
            return cl;
        } else if (t.tsym.precedes(cl.head.tsym, this)) {
            return cl.prepend(t);
        } else {
            // t comes after head, or the two are unrelated
            return insert(cl.tail, t, shouldSkip).prepend(cl.head);
        }
    }

    public List<Type> insert(List<Type> cl, Type t) {
        return insert(cl, t, basicClosureSkip);
    }

    
Form the union of two closures
/**
     * Form the union of two closures
     */
    public List<Type> union(List<Type> cl1, List<Type> cl2, BiPredicate<Type, Type> shouldSkip) {
        if (cl1.isEmpty()) {
            return cl2;
        } else if (cl2.isEmpty()) {
            return cl1;
        } else if (shouldSkip.test(cl1.head, cl2.head)) {
            return union(cl1.tail, cl2.tail, shouldSkip).prepend(cl1.head);
        } else if (cl1.head.tsym.precedes(cl2.head.tsym, this)) {
            return union(cl1.tail, cl2, shouldSkip).prepend(cl1.head);
        } else if (cl2.head.tsym.precedes(cl1.head.tsym, this)) {
            return union(cl1, cl2.tail, shouldSkip).prepend(cl2.head);
        } else {
            // unrelated types
            return union(cl1.tail, cl2, shouldSkip).prepend(cl1.head);
        }
    }

    public List<Type> union(List<Type> cl1, List<Type> cl2) {
        return union(cl1, cl2, basicClosureSkip);
    }

    
Intersect two closures
/**
     * Intersect two closures
     */
    public List<Type> intersect(List<Type> cl1, List<Type> cl2) {
        if (cl1 == cl2)
            return cl1;
        if (cl1.isEmpty() || cl2.isEmpty())
            return List.nil();
        if (cl1.head.tsym.precedes(cl2.head.tsym, this))
            return intersect(cl1.tail, cl2);
        if (cl2.head.tsym.precedes(cl1.head.tsym, this))
            return intersect(cl1, cl2.tail);
        if (isSameType(cl1.head, cl2.head))
            return intersect(cl1.tail, cl2.tail).prepend(cl1.head);
        if (cl1.head.tsym == cl2.head.tsym &&
            cl1.head.hasTag(CLASS) && cl2.head.hasTag(CLASS)) {
            if (cl1.head.isParameterized() && cl2.head.isParameterized()) {
                Type merge = merge(cl1.head,cl2.head);
                return intersect(cl1.tail, cl2.tail).prepend(merge);
            }
            if (cl1.head.isRaw() || cl2.head.isRaw())
                return intersect(cl1.tail, cl2.tail).prepend(erasure(cl1.head));
        }
        return intersect(cl1.tail, cl2.tail);
    }
    // where
        class TypePair {
            final Type t1;
            final Type t2;;

            TypePair(Type t1, Type t2) {
                this.t1 = t1;
                this.t2 = t2;
            }
            @Override
            public int hashCode() {
                return 127 * Types.this.hashCode(t1) + Types.this.hashCode(t2);
            }
            @Override
            public boolean equals(Object obj) {
                if (!(obj instanceof TypePair))
                    return false;
                TypePair typePair = (TypePair)obj;
                return isSameType(t1, typePair.t1)
                    && isSameType(t2, typePair.t2);
            }
        }
        Set<TypePair> mergeCache = new HashSet<>();
        private Type merge(Type c1, Type c2) {
            ClassType class1 = (ClassType) c1;
            List<Type> act1 = class1.getTypeArguments();
            ClassType class2 = (ClassType) c2;
            List<Type> act2 = class2.getTypeArguments();
            ListBuffer<Type> merged = new ListBuffer<>();
            List<Type> typarams = class1.tsym.type.getTypeArguments();

            while (act1.nonEmpty() && act2.nonEmpty() && typarams.nonEmpty()) {
                if (containsType(act1.head, act2.head)) {
                    merged.append(act1.head);
                } else if (containsType(act2.head, act1.head)) {
                    merged.append(act2.head);
                } else {
                    TypePair pair = new TypePair(c1, c2);
                    Type m;
                    if (mergeCache.add(pair)) {
                        m = new WildcardType(lub(wildUpperBound(act1.head),
                                                 wildUpperBound(act2.head)),
                                             BoundKind.EXTENDS,
                                             syms.boundClass);
                        mergeCache.remove(pair);
                    } else {
                        m = new WildcardType(syms.objectType,
                                             BoundKind.UNBOUND,
                                             syms.boundClass);
                    }
                    merged.append(m.withTypeVar(typarams.head));
                }
                act1 = act1.tail;
                act2 = act2.tail;
                typarams = typarams.tail;
            }
            Assert.check(act1.isEmpty() && act2.isEmpty() && typarams.isEmpty());
            // There is no spec detailing how type annotations are to
            // be inherited.  So set it to noAnnotations for now
            return new ClassType(class1.getEnclosingType(), merged.toList(),
                                 class1.tsym);
        }

    
Return the minimum type of a closure, a compound type if no
unique minimum exists.
/**
     * Return the minimum type of a closure, a compound type if no
     * unique minimum exists.
     */
    private Type compoundMin(List<Type> cl) {
        if (cl.isEmpty()) return syms.objectType;
        List<Type> compound = closureMin(cl);
        if (compound.isEmpty())
            return null;
        else if (compound.tail.isEmpty())
            return compound.head;
        else
            return makeIntersectionType(compound);
    }

    
Return the minimum types of a closure, suitable for computing
compoundMin or glb.
/**
     * Return the minimum types of a closure, suitable for computing
     * compoundMin or glb.
     */
    private List<Type> closureMin(List<Type> cl) {
        ListBuffer<Type> classes = new ListBuffer<>();
        ListBuffer<Type> interfaces = new ListBuffer<>();
        Set<Type> toSkip = new HashSet<>();
        while (!cl.isEmpty()) {
            Type current = cl.head;
            boolean keep = !toSkip.contains(current);
            if (keep && current.hasTag(TYPEVAR)) {
                // skip lower-bounded variables with a subtype in cl.tail
                for (Type t : cl.tail) {
                    if (isSubtypeNoCapture(t, current)) {
                        keep = false;
                        break;
                    }
                }
            }
            if (keep) {
                if (current.isInterface())
                    interfaces.append(current);
                else
                    classes.append(current);
                for (Type t : cl.tail) {
                    // skip supertypes of 'current' in cl.tail
                    if (isSubtypeNoCapture(current, t))
                        toSkip.add(t);
                }
            }
            cl = cl.tail;
        }
        return classes.appendList(interfaces).toList();
    }

    
Return the least upper bound of list of types.  if the lub does
not exist return null.
/**
     * Return the least upper bound of list of types.  if the lub does
     * not exist return null.
     */
    public Type lub(List<Type> ts) {
        return lub(ts.toArray(new Type[ts.length()]));
    }

    
Return the least upper bound (lub) of set of types.  If the lub
does not exist return the type of null (bottom).
/**
     * Return the least upper bound (lub) of set of types.  If the lub
     * does not exist return the type of null (bottom).
     */
    public Type lub(Type... ts) {
        final int UNKNOWN_BOUND = 0;
        final int ARRAY_BOUND = 1;
        final int CLASS_BOUND = 2;

        int[] kinds = new int[ts.length];

        int boundkind = UNKNOWN_BOUND;
        for (int i = 0 ; i < ts.length ; i++) {
            Type t = ts[i];
            switch (t.getTag()) {
            case CLASS:
                boundkind |= kinds[i] = CLASS_BOUND;
                break;
            case ARRAY:
                boundkind |= kinds[i] = ARRAY_BOUND;
                break;
            case  TYPEVAR:
                do {
                    t = t.getUpperBound();
                } while (t.hasTag(TYPEVAR));
                if (t.hasTag(ARRAY)) {
                    boundkind |= kinds[i] = ARRAY_BOUND;
                } else {
                    boundkind |= kinds[i] = CLASS_BOUND;
                }
                break;
            default:
                kinds[i] = UNKNOWN_BOUND;
                if (t.isPrimitive())
                    return syms.errType;
            }
        }
        switch (boundkind) {
        case 0:
            return syms.botType;

        case ARRAY_BOUND:
            // calculate lub(A[], B[])
            Type[] elements = new Type[ts.length];
            for (int i = 0 ; i < ts.length ; i++) {
                Type elem = elements[i] = elemTypeFun.apply(ts[i]);
                if (elem.isPrimitive()) {
                    // if a primitive type is found, then return
                    // arraySuperType unless all the types are the
                    // same
                    Type first = ts[0];
                    for (int j = 1 ; j < ts.length ; j++) {
                        if (!isSameType(first, ts[j])) {
                             // lub(int[], B[]) is Cloneable & Serializable
                            return arraySuperType();
                        }
                    }
                    // all the array types are the same, return one
                    // lub(int[], int[]) is int[]
                    return first;
                }
            }
            // lub(A[], B[]) is lub(A, B)[]
            return new ArrayType(lub(elements), syms.arrayClass);

        case CLASS_BOUND:
            // calculate lub(A, B)
            int startIdx = 0;
            for (int i = 0; i < ts.length ; i++) {
                Type t = ts[i];
                if (t.hasTag(CLASS) || t.hasTag(TYPEVAR)) {
                    break;
                } else {
                    startIdx++;
                }
            }
            Assert.check(startIdx < ts.length);
            //step 1 - compute erased candidate set (EC)
            List<Type> cl = erasedSupertypes(ts[startIdx]);
            for (int i = startIdx + 1 ; i < ts.length ; i++) {
                Type t = ts[i];
                if (t.hasTag(CLASS) || t.hasTag(TYPEVAR))
                    cl = intersect(cl, erasedSupertypes(t));
            }
            //step 2 - compute minimal erased candidate set (MEC)
            List<Type> mec = closureMin(cl);
            //step 3 - for each element G in MEC, compute lci(Inv(G))
            List<Type> candidates = List.nil();
            for (Type erasedSupertype : mec) {
                List<Type> lci = List.of(asSuper(ts[startIdx], erasedSupertype.tsym));
                for (int i = startIdx + 1 ; i < ts.length ; i++) {
                    Type superType = asSuper(ts[i], erasedSupertype.tsym);
                    lci = intersect(lci, superType != null ? List.of(superType) : List.nil());
                }
                candidates = candidates.appendList(lci);
            }
            //step 4 - let MEC be { G1, G2 ... Gn }, then we have that
            //lub = lci(Inv(G1)) & lci(Inv(G2)) & ... & lci(Inv(Gn))
            return compoundMin(candidates);

        default:
            // calculate lub(A, B[])
            List<Type> classes = List.of(arraySuperType());
            for (int i = 0 ; i < ts.length ; i++) {
                if (kinds[i] != ARRAY_BOUND) // Filter out any arrays
                    classes = classes.prepend(ts[i]);
            }
            // lub(A, B[]) is lub(A, arraySuperType)
            return lub(classes);
        }
    }
    // where
        List<Type> erasedSupertypes(Type t) {
            ListBuffer<Type> buf = new ListBuffer<>();
            for (Type sup : closure(t)) {
                if (sup.hasTag(TYPEVAR)) {
                    buf.append(sup);
                } else {
                    buf.append(erasure(sup));
                }
            }
            return buf.toList();
        }

        private Type arraySuperType = null;
        private Type arraySuperType() {
            // initialized lazily to avoid problems during compiler startup
            if (arraySuperType == null) {
                synchronized (this) {
                    if (arraySuperType == null) {
                        // JLS 10.8: all arrays implement Cloneable and Serializable.
                        arraySuperType = makeIntersectionType(List.of(syms.serializableType,
                                syms.cloneableType), true);
                    }
                }
            }
            return arraySuperType;
        }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Greatest lower bound">
    public Type glb(List<Type> ts) {
        Type t1 = ts.head;
        for (Type t2 : ts.tail) {
            if (t1.isErroneous())
                return t1;
            t1 = glb(t1, t2);
        }
        return t1;
    }
    //where
    public Type glb(Type t, Type s) {
        if (s == null)
            return t;
        else if (t.isPrimitive() || s.isPrimitive())
            return syms.errType;
        else if (isSubtypeNoCapture(t, s))
            return t;
        else if (isSubtypeNoCapture(s, t))
            return s;

        List<Type> closure = union(closure(t), closure(s));
        return glbFlattened(closure, t);
    }
    //where
    
Perform glb for a list of non-primitive, non-error, non-compound types; redundant elements are removed. Bounds should be ordered according to Symbol.precedes(TypeSymbol, Types). 
Params:
flatBounds – List of type to glb
errT – Original type to use if the result is an error type/**
     * Perform glb for a list of non-primitive, non-error, non-compound types;
     * redundant elements are removed.  Bounds should be ordered according to
     * {@link Symbol#precedes(TypeSymbol,Types)}.
     *
     * @param flatBounds List of type to glb
     * @param errT Original type to use if the result is an error type
     */
    private Type glbFlattened(List<Type> flatBounds, Type errT) {
        List<Type> bounds = closureMin(flatBounds);

        if (bounds.isEmpty()) {             // length == 0
            return syms.objectType;
        } else if (bounds.tail.isEmpty()) { // length == 1
            return bounds.head;
        } else {                            // length > 1
            int classCount = 0;
            List<Type> cvars = List.nil();
            List<Type> lowers = List.nil();
            for (Type bound : bounds) {
                if (!bound.isInterface()) {
                    classCount++;
                    Type lower = cvarLowerBound(bound);
                    if (bound != lower && !lower.hasTag(BOT)) {
                        cvars = cvars.append(bound);
                        lowers = lowers.append(lower);
                    }
                }
            }
            if (classCount > 1) {
                if (lowers.isEmpty()) {
                    return createErrorType(errT);
                } else {
                    // try again with lower bounds included instead of capture variables
                    List<Type> newBounds = bounds.diff(cvars).appendList(lowers);
                    return glb(newBounds);
                }
            }
        }
        return makeIntersectionType(bounds);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="hashCode">
    
Compute a hash code on a type.
/**
     * Compute a hash code on a type.
     */
    public int hashCode(Type t) {
        return hashCode(t, false);
    }

    public int hashCode(Type t, boolean strict) {
        return strict ?
                hashCodeStrictVisitor.visit(t) :
                hashCodeVisitor.visit(t);
    }
    // where
        private static final HashCodeVisitor hashCodeVisitor = new HashCodeVisitor();
        private static final HashCodeVisitor hashCodeStrictVisitor = new HashCodeVisitor() {
            @Override
            public Integer visitTypeVar(TypeVar t, Void ignored) {
                return System.identityHashCode(t);
            }
        };

        private static class HashCodeVisitor extends UnaryVisitor<Integer> {
            public Integer visitType(Type t, Void ignored) {
                return t.getTag().ordinal();
            }

            @Override
            public Integer visitClassType(ClassType t, Void ignored) {
                int result = visit(t.getEnclosingType());
                result *= 127;
                result += t.tsym.flatName().hashCode();
                for (Type s : t.getTypeArguments()) {
                    result *= 127;
                    result += visit(s);
                }
                return result;
            }

            @Override
            public Integer visitMethodType(MethodType t, Void ignored) {
                int h = METHOD.ordinal();
                for (List<Type> thisargs = t.argtypes;
                     thisargs.tail != null;
                     thisargs = thisargs.tail)
                    h = (h << 5) + visit(thisargs.head);
                return (h << 5) + visit(t.restype);
            }

            @Override
            public Integer visitWildcardType(WildcardType t, Void ignored) {
                int result = t.kind.hashCode();
                if (t.type != null) {
                    result *= 127;
                    result += visit(t.type);
                }
                return result;
            }

            @Override
            public Integer visitArrayType(ArrayType t, Void ignored) {
                return visit(t.elemtype) + 12;
            }

            @Override
            public Integer visitTypeVar(TypeVar t, Void ignored) {
                return System.identityHashCode(t);
            }

            @Override
            public Integer visitUndetVar(UndetVar t, Void ignored) {
                return System.identityHashCode(t);
            }

            @Override
            public Integer visitErrorType(ErrorType t, Void ignored) {
                return 0;
            }
        }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Return-Type-Substitutable">
    
Does t have a result that is a subtype of the result type of s,
suitable for covariant returns?  It is assumed that both types
are (possibly polymorphic) method types.  Monomorphic method
types are handled in the obvious way.  Polymorphic method types
require renaming all type variables of one to corresponding
type variables in the other, where correspondence is by
position in the type parameter list. /**
     * Does t have a result that is a subtype of the result type of s,
     * suitable for covariant returns?  It is assumed that both types
     * are (possibly polymorphic) method types.  Monomorphic method
     * types are handled in the obvious way.  Polymorphic method types
     * require renaming all type variables of one to corresponding
     * type variables in the other, where correspondence is by
     * position in the type parameter list. */
    public boolean resultSubtype(Type t, Type s, Warner warner) {
        List<Type> tvars = t.getTypeArguments();
        List<Type> svars = s.getTypeArguments();
        Type tres = t.getReturnType();
        Type sres = subst(s.getReturnType(), svars, tvars);
        return covariantReturnType(tres, sres, warner);
    }

    
Return-Type-Substitutable.
@jls
section 8.4.5/**
     * Return-Type-Substitutable.
     * @jls section 8.4.5
     */
    public boolean returnTypeSubstitutable(Type r1, Type r2) {
        if (hasSameArgs(r1, r2))
            return resultSubtype(r1, r2, noWarnings);
        else
            return covariantReturnType(r1.getReturnType(),
                                       erasure(r2.getReturnType()),
                                       noWarnings);
    }

    public boolean returnTypeSubstitutable(Type r1,
                                           Type r2, Type r2res,
                                           Warner warner) {
        if (isSameType(r1.getReturnType(), r2res))
            return true;
        if (r1.getReturnType().isPrimitive() || r2res.isPrimitive())
            return false;

        if (hasSameArgs(r1, r2))
            return covariantReturnType(r1.getReturnType(), r2res, warner);
        if (isSubtypeUnchecked(r1.getReturnType(), r2res, warner))
            return true;
        if (!isSubtype(r1.getReturnType(), erasure(r2res)))
            return false;
        warner.warn(LintCategory.UNCHECKED);
        return true;
    }

    
Is t an appropriate return type in an overrider for a
method that returns s?
/**
     * Is t an appropriate return type in an overrider for a
     * method that returns s?
     */
    public boolean covariantReturnType(Type t, Type s, Warner warner) {
        return
            isSameType(t, s) ||
            !t.isPrimitive() &&
            !s.isPrimitive() &&
            isAssignable(t, s, warner);
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Box/unbox support">
    
Return the class that boxes the given primitive.
/**
     * Return the class that boxes the given primitive.
     */
    public ClassSymbol boxedClass(Type t) {
        return syms.enterClass(syms.java_base, syms.boxedName[t.getTag().ordinal()]);
    }

    
Return the boxed type if 't' is primitive, otherwise return 't' itself.
/**
     * Return the boxed type if 't' is primitive, otherwise return 't' itself.
     */
    public Type boxedTypeOrType(Type t) {
        return t.isPrimitive() ?
            boxedClass(t).type :
            t;
    }

    
Return the primitive type corresponding to a boxed type.
/**
     * Return the primitive type corresponding to a boxed type.
     */
    public Type unboxedType(Type t) {
        for (int i=0; i<syms.boxedName.length; i++) {
            Name box = syms.boxedName[i];
            if (box != null &&
                asSuper(t, syms.enterClass(syms.java_base, box)) != null)
                return syms.typeOfTag[i];
        }
        return Type.noType;
    }

    
Return the unboxed type if 't' is a boxed class, otherwise return 't' itself.
/**
     * Return the unboxed type if 't' is a boxed class, otherwise return 't' itself.
     */
    public Type unboxedTypeOrType(Type t) {
        Type unboxedType = unboxedType(t);
        return unboxedType.hasTag(NONE) ? t : unboxedType;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Capture conversion">
    /*
     * JLS 5.1.10 Capture Conversion:
     *
     * Let G name a generic type declaration with n formal type
     * parameters A1 ... An with corresponding bounds U1 ... Un. There
     * exists a capture conversion from G<T1 ... Tn> to G<S1 ... Sn>,
     * where, for 1 <= i <= n:
     *
     * + If Ti is a wildcard type argument (4.5.1) of the form ? then
     *   Si is a fresh type variable whose upper bound is
     *   Ui[A1 := S1, ..., An := Sn] and whose lower bound is the null
     *   type.
     *
     * + If Ti is a wildcard type argument of the form ? extends Bi,
     *   then Si is a fresh type variable whose upper bound is
     *   glb(Bi, Ui[A1 := S1, ..., An := Sn]) and whose lower bound is
     *   the null type, where glb(V1,... ,Vm) is V1 & ... & Vm. It is
     *   a compile-time error if for any two classes (not interfaces)
     *   Vi and Vj,Vi is not a subclass of Vj or vice versa.
     *
     * + If Ti is a wildcard type argument of the form ? super Bi,
     *   then Si is a fresh type variable whose upper bound is
     *   Ui[A1 := S1, ..., An := Sn] and whose lower bound is Bi.
     *
     * + Otherwise, Si = Ti.
     *
     * Capture conversion on any type other than a parameterized type
     * (4.5) acts as an identity conversion (5.1.1). Capture
     * conversions never require a special action at run time and
     * therefore never throw an exception at run time.
     *
     * Capture conversion is not applied recursively.
     */
    
Capture conversion as specified by the JLS.
/**
     * Capture conversion as specified by the JLS.
     */

    public List<Type> capture(List<Type> ts) {
        List<Type> buf = List.nil();
        for (Type t : ts) {
            buf = buf.prepend(capture(t));
        }
        return buf.reverse();
    }

    public Type capture(Type t) {
        if (!t.hasTag(CLASS)) {
            return t;
        }
        if (t.getEnclosingType() != Type.noType) {
            Type capturedEncl = capture(t.getEnclosingType());
            if (capturedEncl != t.getEnclosingType()) {
                Type type1 = memberType(capturedEncl, t.tsym);
                t = subst(type1, t.tsym.type.getTypeArguments(), t.getTypeArguments());
            }
        }
        ClassType cls = (ClassType)t;
        if (cls.isRaw() || !cls.isParameterized())
            return cls;

        ClassType G = (ClassType)cls.asElement().asType();
        List<Type> A = G.getTypeArguments();
        List<Type> T = cls.getTypeArguments();
        List<Type> S = freshTypeVariables(T);

        List<Type> currentA = A;
        List<Type> currentT = T;
        List<Type> currentS = S;
        boolean captured = false;
        while (!currentA.isEmpty() &&
               !currentT.isEmpty() &&
               !currentS.isEmpty()) {
            if (currentS.head != currentT.head) {
                captured = true;
                WildcardType Ti = (WildcardType)currentT.head;
                Type Ui = currentA.head.getUpperBound();
                CapturedType Si = (CapturedType)currentS.head;
                if (Ui == null)
                    Ui = syms.objectType;
                switch (Ti.kind) {
                case UNBOUND:
                    Si.setUpperBound( subst(Ui, A, S) );
                    Si.lower = syms.botType;
                    break;
                case EXTENDS:
                    Si.setUpperBound( glb(Ti.getExtendsBound(), subst(Ui, A, S)) );
                    Si.lower = syms.botType;
                    break;
                case SUPER:
                    Si.setUpperBound( subst(Ui, A, S) );
                    Si.lower = Ti.getSuperBound();
                    break;
                }
                Type tmpBound = Si.getUpperBound().hasTag(UNDETVAR) ? ((UndetVar)Si.getUpperBound()).qtype : Si.getUpperBound();
                Type tmpLower = Si.lower.hasTag(UNDETVAR) ? ((UndetVar)Si.lower).qtype : Si.lower;
                if (!Si.getUpperBound().hasTag(ERROR) &&
                    !Si.lower.hasTag(ERROR) &&
                    isSameType(tmpBound, tmpLower)) {
                    currentS.head = Si.getUpperBound();
                }
            }
            currentA = currentA.tail;
            currentT = currentT.tail;
            currentS = currentS.tail;
        }
        if (!currentA.isEmpty() || !currentT.isEmpty() || !currentS.isEmpty())
            return erasure(t); // some "rare" type involved

        if (captured)
            return new ClassType(cls.getEnclosingType(), S, cls.tsym,
                                 cls.getMetadata());
        else
            return t;
    }
    // where
        public List<Type> freshTypeVariables(List<Type> types) {
            ListBuffer<Type> result = new ListBuffer<>();
            for (Type t : types) {
                if (t.hasTag(WILDCARD)) {
                    Type bound = ((WildcardType)t).getExtendsBound();
                    if (bound == null)
                        bound = syms.objectType;
                    result.append(new CapturedType(capturedName,
                                                   syms.noSymbol,
                                                   bound,
                                                   syms.botType,
                                                   (WildcardType)t));
                } else {
                    result.append(t);
                }
            }
            return result.toList();
        }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Internal utility methods">
    private boolean sideCast(Type from, Type to, Warner warn) {
        // We are casting from type $from$ to type $to$, which are
        // non-final unrelated types.  This method
        // tries to reject a cast by transferring type parameters
        // from $to$ to $from$ by common superinterfaces.
        boolean reverse = false;
        Type target = to;
        if ((to.tsym.flags() & INTERFACE) == 0) {
            Assert.check((from.tsym.flags() & INTERFACE) != 0);
            reverse = true;
            to = from;
            from = target;
        }
        List<Type> commonSupers = superClosure(to, erasure(from));
        boolean giveWarning = commonSupers.isEmpty();
        // The arguments to the supers could be unified here to
        // get a more accurate analysis
        while (commonSupers.nonEmpty()) {
            Type t1 = asSuper(from, commonSupers.head.tsym);
            Type t2 = commonSupers.head; // same as asSuper(to, commonSupers.head.tsym);
            if (disjointTypes(t1.getTypeArguments(), t2.getTypeArguments()))
                return false;
            giveWarning = giveWarning || (reverse ? giveWarning(t2, t1) : giveWarning(t1, t2));
            commonSupers = commonSupers.tail;
        }
        if (giveWarning && !isReifiable(reverse ? from : to))
            warn.warn(LintCategory.UNCHECKED);
        return true;
    }

    private boolean sideCastFinal(Type from, Type to, Warner warn) {
        // We are casting from type $from$ to type $to$, which are
        // unrelated types one of which is final and the other of
        // which is an interface.  This method
        // tries to reject a cast by transferring type parameters
        // from the final class to the interface.
        boolean reverse = false;
        Type target = to;
        if ((to.tsym.flags() & INTERFACE) == 0) {
            Assert.check((from.tsym.flags() & INTERFACE) != 0);
            reverse = true;
            to = from;
            from = target;
        }
        Assert.check((from.tsym.flags() & FINAL) != 0);
        Type t1 = asSuper(from, to.tsym);
        if (t1 == null) return false;
        Type t2 = to;
        if (disjointTypes(t1.getTypeArguments(), t2.getTypeArguments()))
            return false;
        if (!isReifiable(target) &&
            (reverse ? giveWarning(t2, t1) : giveWarning(t1, t2)))
            warn.warn(LintCategory.UNCHECKED);
        return true;
    }

    private boolean giveWarning(Type from, Type to) {
        List<Type> bounds = to.isCompound() ?
                directSupertypes(to) : List.of(to);
        for (Type b : bounds) {
            Type subFrom = asSub(from, b.tsym);
            if (b.isParameterized() &&
                    (!(isUnbounded(b) ||
                    isSubtype(from, b) ||
                    ((subFrom != null) && containsType(b.allparams(), subFrom.allparams()))))) {
                return true;
            }
        }
        return false;
    }

    private List<Type> superClosure(Type t, Type s) {
        List<Type> cl = List.nil();
        for (List<Type> l = interfaces(t); l.nonEmpty(); l = l.tail) {
            if (isSubtype(s, erasure(l.head))) {
                cl = insert(cl, l.head);
            } else {
                cl = union(cl, superClosure(l.head, s));
            }
        }
        return cl;
    }

    private boolean containsTypeEquivalent(Type t, Type s) {
        return isSameType(t, s) || // shortcut
            containsType(t, s) && containsType(s, t);
    }

    // <editor-fold defaultstate="collapsed" desc="adapt">
    
Adapt a type by computing a substitution which maps a source
type to a target type.
Params:
source –    the source type
target –    the target type
from –      the type variables of the computed substitution
to –        the types of the computed substitution./**
     * Adapt a type by computing a substitution which maps a source
     * type to a target type.
     *
     * @param source    the source type
     * @param target    the target type
     * @param from      the type variables of the computed substitution
     * @param to        the types of the computed substitution.
     */
    public void adapt(Type source,
                       Type target,
                       ListBuffer<Type> from,
                       ListBuffer<Type> to) throws AdaptFailure {
        new Adapter(from, to).adapt(source, target);
    }

    class Adapter extends SimpleVisitor<Void, Type> {

        ListBuffer<Type> from;
        ListBuffer<Type> to;
        Map<Symbol,Type> mapping;

        Adapter(ListBuffer<Type> from, ListBuffer<Type> to) {
            this.from = from;
            this.to = to;
            mapping = new HashMap<>();
        }

        public void adapt(Type source, Type target) throws AdaptFailure {
            visit(source, target);
            List<Type> fromList = from.toList();
            List<Type> toList = to.toList();
            while (!fromList.isEmpty()) {
                Type val = mapping.get(fromList.head.tsym);
                if (toList.head != val)
                    toList.head = val;
                fromList = fromList.tail;
                toList = toList.tail;
            }
        }

        @Override
        public Void visitClassType(ClassType source, Type target) throws AdaptFailure {
            if (target.hasTag(CLASS))
                adaptRecursive(source.allparams(), target.allparams());
            return null;
        }

        @Override
        public Void visitArrayType(ArrayType source, Type target) throws AdaptFailure {
            if (target.hasTag(ARRAY))
                adaptRecursive(elemtype(source), elemtype(target));
            return null;
        }

        @Override
        public Void visitWildcardType(WildcardType source, Type target) throws AdaptFailure {
            if (source.isExtendsBound())
                adaptRecursive(wildUpperBound(source), wildUpperBound(target));
            else if (source.isSuperBound())
                adaptRecursive(wildLowerBound(source), wildLowerBound(target));
            return null;
        }

        @Override
        public Void visitTypeVar(TypeVar source, Type target) throws AdaptFailure {
            // Check to see if there is
            // already a mapping for $source$, in which case
            // the old mapping will be merged with the new
            Type val = mapping.get(source.tsym);
            if (val != null) {
                if (val.isSuperBound() && target.isSuperBound()) {
                    val = isSubtype(wildLowerBound(val), wildLowerBound(target))
                        ? target : val;
                } else if (val.isExtendsBound() && target.isExtendsBound()) {
                    val = isSubtype(wildUpperBound(val), wildUpperBound(target))
                        ? val : target;
                } else if (!isSameType(val, target)) {
                    throw new AdaptFailure();
                }
            } else {
                val = target;
                from.append(source);
                to.append(target);
            }
            mapping.put(source.tsym, val);
            return null;
        }

        @Override
        public Void visitType(Type source, Type target) {
            return null;
        }

        private Set<TypePair> cache = new HashSet<>();

        private void adaptRecursive(Type source, Type target) {
            TypePair pair = new TypePair(source, target);
            if (cache.add(pair)) {
                try {
                    visit(source, target);
                } finally {
                    cache.remove(pair);
                }
            }
        }

        private void adaptRecursive(List<Type> source, List<Type> target) {
            if (source.length() == target.length()) {
                while (source.nonEmpty()) {
                    adaptRecursive(source.head, target.head);
                    source = source.tail;
                    target = target.tail;
                }
            }
        }
    }

    public static class AdaptFailure extends RuntimeException {
        static final long serialVersionUID = -7490231548272701566L;
    }

    private void adaptSelf(Type t,
                           ListBuffer<Type> from,
                           ListBuffer<Type> to) {
        try {
            //if (t.tsym.type != t)
                adapt(t.tsym.type, t, from, to);
        } catch (AdaptFailure ex) {
            // Adapt should never fail calculating a mapping from
            // t.tsym.type to t as there can be no merge problem.
            throw new AssertionError(ex);
        }
    }
    // </editor-fold>

    
Rewrite all type variables (universal quantifiers) in the given type to wildcards (existential quantifiers). This is used to determine if a cast is allowed. For example, if high is true and T <: Number, then List<T> is rewritten to List<?  extends Number>. Since List<Integer> <:
List<? extends Number> a List<T> can be cast to 
List<Integer> with a warning. 
Params:
t – a type
high – if true return an upper bound; otherwise a lower
bound
rewriteTypeVars – only rewrite captured wildcards if false;
otherwise rewrite all type variables
Returns:
the type rewritten with wildcards (existential
quantifiers) only/**
     * Rewrite all type variables (universal quantifiers) in the given
     * type to wildcards (existential quantifiers).  This is used to
     * determine if a cast is allowed.  For example, if high is true
     * and {@code T <: Number}, then {@code List<T>} is rewritten to
     * {@code List<?  extends Number>}.  Since {@code List<Integer> <:
     * List<? extends Number>} a {@code List<T>} can be cast to {@code
     * List<Integer>} with a warning.
     * @param t a type
     * @param high if true return an upper bound; otherwise a lower
     * bound
     * @param rewriteTypeVars only rewrite captured wildcards if false;
     * otherwise rewrite all type variables
     * @return the type rewritten with wildcards (existential
     * quantifiers) only
     */
    private Type rewriteQuantifiers(Type t, boolean high, boolean rewriteTypeVars) {
        return new Rewriter(high, rewriteTypeVars).visit(t);
    }

    class Rewriter extends UnaryVisitor<Type> {

        boolean high;
        boolean rewriteTypeVars;

        Rewriter(boolean high, boolean rewriteTypeVars) {
            this.high = high;
            this.rewriteTypeVars = rewriteTypeVars;
        }

        @Override
        public Type visitClassType(ClassType t, Void s) {
            ListBuffer<Type> rewritten = new ListBuffer<>();
            boolean changed = false;
            for (Type arg : t.allparams()) {
                Type bound = visit(arg);
                if (arg != bound) {
                    changed = true;
                }
                rewritten.append(bound);
            }
            if (changed)
                return subst(t.tsym.type,
                        t.tsym.type.allparams(),
                        rewritten.toList());
            else
                return t;
        }

        public Type visitType(Type t, Void s) {
            return t;
        }

        @Override
        public Type visitCapturedType(CapturedType t, Void s) {
            Type w_bound = t.wildcard.type;
            Type bound = w_bound.contains(t) ?
                        erasure(w_bound) :
                        visit(w_bound);
            return rewriteAsWildcardType(visit(bound), t.wildcard.bound, t.wildcard.kind);
        }

        @Override
        public Type visitTypeVar(TypeVar t, Void s) {
            if (rewriteTypeVars) {
                Type bound = t.getUpperBound().contains(t) ?
                        erasure(t.getUpperBound()) :
                        visit(t.getUpperBound());
                return rewriteAsWildcardType(bound, t, EXTENDS);
            } else {
                return t;
            }
        }

        @Override
        public Type visitWildcardType(WildcardType t, Void s) {
            Type bound2 = visit(t.type);
            return t.type == bound2 ? t : rewriteAsWildcardType(bound2, t.bound, t.kind);
        }

        private Type rewriteAsWildcardType(Type bound, TypeVar formal, BoundKind bk) {
            switch (bk) {
               case EXTENDS: return high ?
                       makeExtendsWildcard(B(bound), formal) :
                       makeExtendsWildcard(syms.objectType, formal);
               case SUPER: return high ?
                       makeSuperWildcard(syms.botType, formal) :
                       makeSuperWildcard(B(bound), formal);
               case UNBOUND: return makeExtendsWildcard(syms.objectType, formal);
               default:
                   Assert.error("Invalid bound kind " + bk);
                   return null;
            }
        }

        Type B(Type t) {
            while (t.hasTag(WILDCARD)) {
                WildcardType w = (WildcardType)t;
                t = high ?
                    w.getExtendsBound() :
                    w.getSuperBound();
                if (t == null) {
                    t = high ? syms.objectType : syms.botType;
                }
            }
            return t;
        }
    }


    
Create a wildcard with the given upper (extends) bound; create
an unbounded wildcard if bound is Object.
Params:
bound – the upper bound
formal – the formal type parameter that will be
substituted by the wildcard/**
     * Create a wildcard with the given upper (extends) bound; create
     * an unbounded wildcard if bound is Object.
     *
     * @param bound the upper bound
     * @param formal the formal type parameter that will be
     * substituted by the wildcard
     */
    private WildcardType makeExtendsWildcard(Type bound, TypeVar formal) {
        if (bound == syms.objectType) {
            return new WildcardType(syms.objectType,
                                    BoundKind.UNBOUND,
                                    syms.boundClass,
                                    formal);
        } else {
            return new WildcardType(bound,
                                    BoundKind.EXTENDS,
                                    syms.boundClass,
                                    formal);
        }
    }

    
Create a wildcard with the given lower (super) bound; create an unbounded wildcard if bound is bottom (type of null). 
Params:
bound – the lower bound
formal – the formal type parameter that will be
substituted by the wildcard/**
     * Create a wildcard with the given lower (super) bound; create an
     * unbounded wildcard if bound is bottom (type of {@code null}).
     *
     * @param bound the lower bound
     * @param formal the formal type parameter that will be
     * substituted by the wildcard
     */
    private WildcardType makeSuperWildcard(Type bound, TypeVar formal) {
        if (bound.hasTag(BOT)) {
            return new WildcardType(syms.objectType,
                                    BoundKind.UNBOUND,
                                    syms.boundClass,
                                    formal);
        } else {
            return new WildcardType(bound,
                                    BoundKind.SUPER,
                                    syms.boundClass,
                                    formal);
        }
    }

    
A wrapper for a type that allows use in sets.
/**
     * A wrapper for a type that allows use in sets.
     */
    public static class UniqueType {
        public final Type type;
        final Types types;

        public UniqueType(Type type, Types types) {
            this.type = type;
            this.types = types;
        }

        public int hashCode() {
            return types.hashCode(type);
        }

        public boolean equals(Object obj) {
            return (obj instanceof UniqueType) &&
                types.isSameType(type, ((UniqueType)obj).type);
        }

        public String toString() {
            return type.toString();
        }

    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Visitors">
    
A default visitor for types.  All visitor methods except
visitType are implemented by delegating to visitType.  Concrete
subclasses must provide an implementation of visitType and can
override other methods as needed.
Type parameters:
<R> – the return type of the operation implemented by this
visitor; use Void if no return type is needed.
<S> – the type of the second argument (the first being the
type itself) of the operation implemented by this visitor; use
Void if a second argument is not needed./**
     * A default visitor for types.  All visitor methods except
     * visitType are implemented by delegating to visitType.  Concrete
     * subclasses must provide an implementation of visitType and can
     * override other methods as needed.
     *
     * @param <R> the return type of the operation implemented by this
     * visitor; use Void if no return type is needed.
     * @param <S> the type of the second argument (the first being the
     * type itself) of the operation implemented by this visitor; use
     * Void if a second argument is not needed.
     */
    public static abstract class DefaultTypeVisitor<R,S> implements Type.Visitor<R,S> {
        final public R visit(Type t, S s)               { return t.accept(this, s); }
        public R visitClassType(ClassType t, S s)       { return visitType(t, s); }
        public R visitWildcardType(WildcardType t, S s) { return visitType(t, s); }
        public R visitArrayType(ArrayType t, S s)       { return visitType(t, s); }
        public R visitMethodType(MethodType t, S s)     { return visitType(t, s); }
        public R visitPackageType(PackageType t, S s)   { return visitType(t, s); }
        public R visitModuleType(ModuleType t, S s)     { return visitType(t, s); }
        public R visitTypeVar(TypeVar t, S s)           { return visitType(t, s); }
        public R visitCapturedType(CapturedType t, S s) { return visitType(t, s); }
        public R visitForAll(ForAll t, S s)             { return visitType(t, s); }
        public R visitUndetVar(UndetVar t, S s)         { return visitType(t, s); }
        public R visitErrorType(ErrorType t, S s)       { return visitType(t, s); }
    }

    
A default visitor for symbols.  All visitor methods except
visitSymbol are implemented by delegating to visitSymbol.  Concrete
subclasses must provide an implementation of visitSymbol and can
override other methods as needed.
Type parameters:
<R> – the return type of the operation implemented by this
visitor; use Void if no return type is needed.
<S> – the type of the second argument (the first being the
symbol itself) of the operation implemented by this visitor; use
Void if a second argument is not needed./**
     * A default visitor for symbols.  All visitor methods except
     * visitSymbol are implemented by delegating to visitSymbol.  Concrete
     * subclasses must provide an implementation of visitSymbol and can
     * override other methods as needed.
     *
     * @param <R> the return type of the operation implemented by this
     * visitor; use Void if no return type is needed.
     * @param <S> the type of the second argument (the first being the
     * symbol itself) of the operation implemented by this visitor; use
     * Void if a second argument is not needed.
     */
    public static abstract class DefaultSymbolVisitor<R,S> implements Symbol.Visitor<R,S> {
        final public R visit(Symbol s, S arg)                   { return s.accept(this, arg); }
        public R visitClassSymbol(ClassSymbol s, S arg)         { return visitSymbol(s, arg); }
        public R visitMethodSymbol(MethodSymbol s, S arg)       { return visitSymbol(s, arg); }
        public R visitOperatorSymbol(OperatorSymbol s, S arg)   { return visitSymbol(s, arg); }
        public R visitPackageSymbol(PackageSymbol s, S arg)     { return visitSymbol(s, arg); }
        public R visitTypeSymbol(TypeSymbol s, S arg)           { return visitSymbol(s, arg); }
        public R visitVarSymbol(VarSymbol s, S arg)             { return visitSymbol(s, arg); }
    }

    
A simple visitor for types.  This visitor is simple as
captured wildcards, for-all types (generic methods), and
undetermined type variables (part of inference) are hidden.
Captured wildcards are hidden by treating them as type
variables and the rest are hidden by visiting their qtypes.
Type parameters:
<R> – the return type of the operation implemented by this
visitor; use Void if no return type is needed.
<S> – the type of the second argument (the first being the
type itself) of the operation implemented by this visitor; use
Void if a second argument is not needed./**
     * A <em>simple</em> visitor for types.  This visitor is simple as
     * captured wildcards, for-all types (generic methods), and
     * undetermined type variables (part of inference) are hidden.
     * Captured wildcards are hidden by treating them as type
     * variables and the rest are hidden by visiting their qtypes.
     *
     * @param <R> the return type of the operation implemented by this
     * visitor; use Void if no return type is needed.
     * @param <S> the type of the second argument (the first being the
     * type itself) of the operation implemented by this visitor; use
     * Void if a second argument is not needed.
     */
    public static abstract class SimpleVisitor<R,S> extends DefaultTypeVisitor<R,S> {
        @Override
        public R visitCapturedType(CapturedType t, S s) {
            return visitTypeVar(t, s);
        }
        @Override
        public R visitForAll(ForAll t, S s) {
            return visit(t.qtype, s);
        }
        @Override
        public R visitUndetVar(UndetVar t, S s) {
            return visit(t.qtype, s);
        }
    }

    
A plain relation on types.  That is a 2-ary function on the
form Type × Type → Boolean.

/**
     * A plain relation on types.  That is a 2-ary function on the
     * form Type&nbsp;&times;&nbsp;Type&nbsp;&rarr;&nbsp;Boolean.
     * <!-- In plain text: Type x Type -> Boolean -->
     */
    public static abstract class TypeRelation extends SimpleVisitor<Boolean,Type> {}

    
A convenience visitor for implementing operations that only
require one argument (the type itself), that is, unary
operations.
Type parameters:
<R> – the return type of the operation implemented by this
visitor; use Void if no return type is needed./**
     * A convenience visitor for implementing operations that only
     * require one argument (the type itself), that is, unary
     * operations.
     *
     * @param <R> the return type of the operation implemented by this
     * visitor; use Void if no return type is needed.
     */
    public static abstract class UnaryVisitor<R> extends SimpleVisitor<R,Void> {
        final public R visit(Type t) { return t.accept(this, null); }
    }

    
A visitor for implementing a mapping from types to types.  The
default behavior of this class is to implement the identity
mapping (mapping a type to itself).  This can be overridden in
subclasses.
Type parameters:
<S> – the type of the second argument (the first being the
type itself) of this mapping; use Void if a second argument is
not needed./**
     * A visitor for implementing a mapping from types to types.  The
     * default behavior of this class is to implement the identity
     * mapping (mapping a type to itself).  This can be overridden in
     * subclasses.
     *
     * @param <S> the type of the second argument (the first being the
     * type itself) of this mapping; use Void if a second argument is
     * not needed.
     */
    public static class MapVisitor<S> extends DefaultTypeVisitor<Type,S> {
        final public Type visit(Type t) { return t.accept(this, null); }
        public Type visitType(Type t, S s) { return t; }
    }

    
An abstract class for mappings from types to types (see Type.map(TypeMapping<Object>). This class implements the functional interface Function, that allows it to be used fluently in stream-like processing. /**
     * An abstract class for mappings from types to types (see {@link Type#map(TypeMapping)}.
     * This class implements the functional interface {@code Function}, that allows it to be used
     * fluently in stream-like processing.
     */
    public static class TypeMapping<S> extends MapVisitor<S> implements Function<Type, Type> {
        @Override
        public Type apply(Type type) { return visit(type); }

        List<Type> visit(List<Type> ts, S s) {
            return ts.map(t -> visit(t, s));
        }

        @Override
        public Type visitCapturedType(CapturedType t, S s) {
            return visitTypeVar(t, s);
        }
    }
    // </editor-fold>


    // <editor-fold defaultstate="collapsed" desc="Annotation support">

    public RetentionPolicy getRetention(Attribute.Compound a) {
        return getRetention(a.type.tsym);
    }

    public RetentionPolicy getRetention(TypeSymbol sym) {
        RetentionPolicy vis = RetentionPolicy.CLASS; // the default
        Attribute.Compound c = sym.attribute(syms.retentionType.tsym);
        if (c != null) {
            Attribute value = c.member(names.value);
            if (value != null && value instanceof Attribute.Enum) {
                Name levelName = ((Attribute.Enum)value).value.name;
                if (levelName == names.SOURCE) vis = RetentionPolicy.SOURCE;
                else if (levelName == names.CLASS) vis = RetentionPolicy.CLASS;
                else if (levelName == names.RUNTIME) vis = RetentionPolicy.RUNTIME;
                else ;// /* fail soft */ throw new AssertionError(levelName);
            }
        }
        return vis;
    }
    // </editor-fold>

    // <editor-fold defaultstate="collapsed" desc="Signature Generation">

    public static abstract class SignatureGenerator {

        public static class InvalidSignatureException extends RuntimeException {
            private static final long serialVersionUID = 0;

            private final Type type;

            InvalidSignatureException(Type type) {
                this.type = type;
            }

            public Type type() {
                return type;
            }
        }

        private final Types types;

        protected abstract void append(char ch);
        protected abstract void append(byte[] ba);
        protected abstract void append(Name name);
        protected void classReference(ClassSymbol c) { /* by default: no-op */ }

        protected SignatureGenerator(Types types) {
            this.types = types;
        }

        
Assemble signature of given type in string buffer.
/**
         * Assemble signature of given type in string buffer.
         */
        public void assembleSig(Type type) {
            switch (type.getTag()) {
                case BYTE:
                    append('B');
                    break;
                case SHORT:
                    append('S');
                    break;
                case CHAR:
                    append('C');
                    break;
                case INT:
                    append('I');
                    break;
                case LONG:
                    append('J');
                    break;
                case FLOAT:
                    append('F');
                    break;
                case DOUBLE:
                    append('D');
                    break;
                case BOOLEAN:
                    append('Z');
                    break;
                case VOID:
                    append('V');
                    break;
                case CLASS:
                    if (type.isCompound()) {
                        throw new InvalidSignatureException(type);
                    }
                    append('L');
                    assembleClassSig(type);
                    append(';');
                    break;
                case ARRAY:
                    ArrayType at = (ArrayType) type;
                    append('[');
                    assembleSig(at.elemtype);
                    break;
                case METHOD:
                    MethodType mt = (MethodType) type;
                    append('(');
                    assembleSig(mt.argtypes);
                    append(')');
                    assembleSig(mt.restype);
                    if (hasTypeVar(mt.thrown)) {
                        for (List<Type> l = mt.thrown; l.nonEmpty(); l = l.tail) {
                            append('^');
                            assembleSig(l.head);
                        }
                    }
                    break;
                case WILDCARD: {
                    Type.WildcardType ta = (Type.WildcardType) type;
                    switch (ta.kind) {
                        case SUPER:
                            append('-');
                            assembleSig(ta.type);
                            break;
                        case EXTENDS:
                            append('+');
                            assembleSig(ta.type);
                            break;
                        case UNBOUND:
                            append('*');
                            break;
                        default:
                            throw new AssertionError(ta.kind);
                    }
                    break;
                }
                case TYPEVAR:
                    if (((TypeVar)type).isCaptured()) {
                        throw new InvalidSignatureException(type);
                    }
                    append('T');
                    append(type.tsym.name);
                    append(';');
                    break;
                case FORALL:
                    Type.ForAll ft = (Type.ForAll) type;
                    assembleParamsSig(ft.tvars);
                    assembleSig(ft.qtype);
                    break;
                default:
                    throw new AssertionError("typeSig " + type.getTag());
            }
        }

        public boolean hasTypeVar(List<Type> l) {
            while (l.nonEmpty()) {
                if (l.head.hasTag(TypeTag.TYPEVAR)) {
                    return true;
                }
                l = l.tail;
            }
            return false;
        }

        public void assembleClassSig(Type type) {
            ClassType ct = (ClassType) type;
            ClassSymbol c = (ClassSymbol) ct.tsym;
            classReference(c);
            Type outer = ct.getEnclosingType();
            if (outer.allparams().nonEmpty()) {
                boolean rawOuter =
                        c.owner.kind == MTH || // either a local class
                        c.name == types.names.empty; // or anonymous
                assembleClassSig(rawOuter
                        ? types.erasure(outer)
                        : outer);
                append(rawOuter ? '$' : '.');
                Assert.check(c.flatname.startsWith(c.owner.enclClass().flatname));
                append(rawOuter
                        ? c.flatname.subName(c.owner.enclClass().flatname.getByteLength() + 1, c.flatname.getByteLength())
                        : c.name);
            } else {
                append(externalize(c.flatname));
            }
            if (ct.getTypeArguments().nonEmpty()) {
                append('<');
                assembleSig(ct.getTypeArguments());
                append('>');
            }
        }

        public void assembleParamsSig(List<Type> typarams) {
            append('<');
            for (List<Type> ts = typarams; ts.nonEmpty(); ts = ts.tail) {
                Type.TypeVar tvar = (Type.TypeVar) ts.head;
                append(tvar.tsym.name);
                List<Type> bounds = types.getBounds(tvar);
                if ((bounds.head.tsym.flags() & INTERFACE) != 0) {
                    append(':');
                }
                for (List<Type> l = bounds; l.nonEmpty(); l = l.tail) {
                    append(':');
                    assembleSig(l.head);
                }
            }
            append('>');
        }

        private void assembleSig(List<Type> types) {
            for (List<Type> ts = types; ts.nonEmpty(); ts = ts.tail) {
                assembleSig(ts.head);
            }
        }
    }
    // </editor-fold>

    public void newRound() {
        descCache._map.clear();
        isDerivedRawCache.clear();
        implCache._map.clear();
        membersCache._map.clear();
        closureCache.clear();
    }
}