Mercurial > jdk8-mips64-public > langtools / file revision

 /*

  * Copyright (c) 1999, 2008, 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.util.Set;

 import java.util.concurrent.Callable;

 import javax.lang.model.element.*;

 import javax.tools.JavaFileObject;

 import com.sun.tools.javac.util.*;

 import com.sun.tools.javac.util.Name;

 import com.sun.tools.javac.code.Type.*;

 import com.sun.tools.javac.comp.Attr;

 import com.sun.tools.javac.comp.AttrContext;

 import com.sun.tools.javac.comp.Env;

 import com.sun.tools.javac.jvm.*;

 import com.sun.tools.javac.model.*;

 import com.sun.tools.javac.tree.JCTree;

 import static com.sun.tools.javac.code.Flags.*;

 import static com.sun.tools.javac.code.Kinds.*;

 import static com.sun.tools.javac.code.TypeTags.*;

 /** Root class for Java symbols. It contains subclasses

  *  for specific sorts of symbols, such as variables, methods and operators,

  *  types, packages. Each subclass is represented as a static inner class

  *  inside Symbol.

  *

  *  <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 abstract class Symbol implements Element {

     // public Throwable debug = new Throwable();

     /** The kind of this symbol.

      *  @see Kinds

      */

     public int kind;

     /** The flags of this symbol.

      */

     public long flags_field;

     /** An accessor method for the flags of this symbol.

      *  Flags of class symbols should be accessed through the accessor

      *  method to make sure that the class symbol is loaded.

      */

     public long flags() { return flags_field; }

     /** The attributes of this symbol.

      */

     public List<Attribute.Compound> attributes_field;

     /** An accessor method for the attributes of this symbol.

      *  Attributes of class symbols should be accessed through the accessor

      *  method to make sure that the class symbol is loaded.

      */

     public List<Attribute.Compound> getAnnotationMirrors() {

         assert attributes_field != null;

         return attributes_field;

     }

     /** Fetch a particular annotation from a symbol. */

     public Attribute.Compound attribute(Symbol anno) {

         for (Attribute.Compound a : getAnnotationMirrors())

             if (a.type.tsym == anno) return a;

         return null;

     }

     /** The name of this symbol in Utf8 representation.

      */

     public Name name;

     /** The type of this symbol.

      */

     public Type type;

     /** The type annotations targeted to a tree directly owned by this symbol

      */

     // type annotations are stored here for two purposes:

     //  - convenient location to store annotations for generation after erasure

     //  - a private interface for accessing type annotations parsed from

     //    classfiles

     //  the field is populated for the following declaration only

     //  class, field, variable and type parameters

     //

     public List<Attribute.TypeCompound> typeAnnotations;

     /** The owner of this symbol.

      */

     public Symbol owner;

     /** The completer of this symbol.

      */

     public Completer completer;

     /** A cache for the type erasure of this symbol.

      */

     public Type erasure_field;

     /** Construct a symbol with given kind, flags, name, type and owner.

      */

     public Symbol(int kind, long flags, Name name, Type type, Symbol owner) {

         this.kind = kind;

         this.flags_field = flags;

         this.type = type;

         this.owner = owner;

         this.completer = null;

         this.erasure_field = null;

         this.attributes_field = List.nil();

         this.typeAnnotations = List.nil();

         this.name = name;

     }

     /** Clone this symbol with new owner.

      *  Legal only for fields and methods.

      */

     public Symbol clone(Symbol newOwner) {

         throw new AssertionError();

     }

     public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

         return v.visitSymbol(this, p);

     }

     /** The Java source which this symbol represents.

      *  A description of this symbol; overrides Object.

      */

     public String toString() {

         return name.toString();

     }

     /** A Java source description of the location of this symbol; used for

      *  error reporting.

      *

      * @return null if the symbol is a package or a toplevel class defined in

      * the default package; otherwise, the owner symbol is returned

      */

     public Symbol location() {

         if (owner.name == null || (owner.name.isEmpty() && owner.kind != PCK && owner.kind != TYP)) {

             return null;

         }

         return owner;

     }

     public Symbol location(Type site, Types types) {

         if (owner.name == null || owner.name.isEmpty()) {

             return location();

         }

         if (owner.type.tag == CLASS) {

             Type ownertype = types.asOuterSuper(site, owner);

             if (ownertype != null) return ownertype.tsym;

         }

         return owner;

     }

     /** The symbol's erased type.

      */

     public Type erasure(Types types) {

         if (erasure_field == null)

             erasure_field = types.erasure(type);

         return erasure_field;

     }

     /** The external type of a symbol. This is the symbol's erased type

      *  except for constructors of inner classes which get the enclosing

      *  instance class added as first argument.

      */

     public Type externalType(Types types) {

         Type t = erasure(types);

         if (name == name.table.names.init && owner.hasOuterInstance()) {

             Type outerThisType = types.erasure(owner.type.getEnclosingType());

             return new MethodType(t.getParameterTypes().prepend(outerThisType),

                                   t.getReturnType(),

                                   t.getThrownTypes(),

                                   t.tsym);

         } else {

             return t;

         }

     }

     public boolean isStatic() {

         return

             (flags() & STATIC) != 0 ||

             (owner.flags() & INTERFACE) != 0 && kind != MTH;

     }

     public boolean isInterface() {

         return (flags() & INTERFACE) != 0;

     }

     /** Is this symbol declared (directly or indirectly) local

      *  to a method or variable initializer?

      *  Also includes fields of inner classes which are in

      *  turn local to a method or variable initializer.

      */

     public boolean isLocal() {

         return

             (owner.kind & (VAR | MTH)) != 0 ||

             (owner.kind == TYP && owner.isLocal());

     }

     /** Has this symbol an empty name? This includes anonymous

      *  inner classses.

      */

     public boolean isAnonymous() {

         return name.isEmpty();

     }

     /** Is this symbol a constructor?

      */

     public boolean isConstructor() {

         return name == name.table.names.init;

     }

     /** The fully qualified name of this symbol.

      *  This is the same as the symbol's name except for class symbols,

      *  which are handled separately.

      */

     public Name getQualifiedName() {

         return name;

     }

     /** The fully qualified name of this symbol after converting to flat

      *  representation. This is the same as the symbol's name except for

      *  class symbols, which are handled separately.

      */

     public Name flatName() {

         return getQualifiedName();

     }

     /** If this is a class or package, its members, otherwise null.

      */

     public Scope members() {

         return null;

     }

     /** A class is an inner class if it it has an enclosing instance class.

      */

     public boolean isInner() {

         return type.getEnclosingType().tag == CLASS;

     }

     /** An inner class has an outer instance if it is not an interface

      *  it has an enclosing instance class which might be referenced from the class.

      *  Nested classes can see instance members of their enclosing class.

      *  Their constructors carry an additional this$n parameter, inserted

      *  implicitly by the compiler.

      *

      *  @see #isInner

      */

     public boolean hasOuterInstance() {

         return

             type.getEnclosingType().tag == CLASS && (flags() & (INTERFACE | NOOUTERTHIS)) == 0;

     }

     /** The closest enclosing class of this symbol's declaration.

      */

     public ClassSymbol enclClass() {

         Symbol c = this;

         while (c != null &&

                ((c.kind & TYP) == 0 || c.type.tag != CLASS)) {

             c = c.owner;

         }

         return (ClassSymbol)c;

     }

     /** The outermost class which indirectly owns this symbol.

      */

     public ClassSymbol outermostClass() {

         Symbol sym = this;

         Symbol prev = null;

         while (sym.kind != PCK) {

             prev = sym;

             sym = sym.owner;

         }

         return (ClassSymbol) prev;

     }

     /** The package which indirectly owns this symbol.

      */

     public PackageSymbol packge() {

         Symbol sym = this;

         while (sym.kind != PCK) {

             sym = sym.owner;

         }

         return (PackageSymbol) sym;

     }

     /** Is this symbol a subclass of `base'? Only defined for ClassSymbols.

      */

     public boolean isSubClass(Symbol base, Types types) {

         throw new AssertionError("isSubClass " + this);

     }

     /** Fully check membership: hierarchy, protection, and hiding.

      *  Does not exclude methods not inherited due to overriding.

      */

     public boolean isMemberOf(TypeSymbol clazz, Types types) {

         return

             owner == clazz ||

             clazz.isSubClass(owner, types) &&

             isInheritedIn(clazz, types) &&

             !hiddenIn((ClassSymbol)clazz, types);

     }

     /** Is this symbol the same as or enclosed by the given class? */

     public boolean isEnclosedBy(ClassSymbol clazz) {

         for (Symbol sym = this; sym.kind != PCK; sym = sym.owner)

             if (sym == clazz) return true;

         return false;

     }

     /** Check for hiding.  Note that this doesn't handle multiple

      *  (interface) inheritance. */

     private boolean hiddenIn(ClassSymbol clazz, Types types) {

         if (kind == MTH && (flags() & STATIC) == 0) return false;

         while (true) {

             if (owner == clazz) return false;

             Scope.Entry e = clazz.members().lookup(name);

             while (e.scope != null) {

                 if (e.sym == this) return false;

                 if (e.sym.kind == kind &&

                     (kind != MTH ||

                      (e.sym.flags() & STATIC) != 0 &&

                      types.isSubSignature(e.sym.type, type)))

                     return true;

                 e = e.next();

             }

             Type superType = types.supertype(clazz.type);

             if (superType.tag != TypeTags.CLASS) return false;

             clazz = (ClassSymbol)superType.tsym;

         }

     }

     /** Is this symbol inherited into a given class?

      *  PRE: If symbol's owner is a interface,

      *       it is already assumed that the interface is a superinterface

      *       of given class.

      *  @param clazz  The class for which we want to establish membership.

      *                This must be a subclass of the member's owner.

      */

     public boolean isInheritedIn(Symbol clazz, Types types) {

         switch ((int)(flags_field & Flags.AccessFlags)) {

         default: // error recovery

         case PUBLIC:

             return true;

         case PRIVATE:

             return this.owner == clazz;

         case PROTECTED:

             // we model interfaces as extending Object

             return (clazz.flags() & INTERFACE) == 0;

         case 0:

             PackageSymbol thisPackage = this.packge();

             for (Symbol sup = clazz;

                  sup != null && sup != this.owner;

                  sup = types.supertype(sup.type).tsym) {

                 while (sup.type.tag == TYPEVAR)

                     sup = sup.type.getUpperBound().tsym;

                 if (sup.type.isErroneous())

                     return true; // error recovery

                 if ((sup.flags() & COMPOUND) != 0)

                     continue;

                 if (sup.packge() != thisPackage)

                     return false;

             }

             return (clazz.flags() & INTERFACE) == 0;

         }

     }

     /** The (variable or method) symbol seen as a member of given

      *  class type`site' (this might change the symbol's type).

      *  This is used exclusively for producing diagnostics.

      */

     public Symbol asMemberOf(Type site, Types types) {

         throw new AssertionError();

     }

     /** Does this method symbol override `other' symbol, when both are seen as

      *  members of class `origin'?  It is assumed that _other is a member

      *  of origin.

      *

      *  It is assumed that both symbols have the same name.  The static

      *  modifier is ignored for this test.

      *

      *  See JLS 8.4.6.1 (without transitivity) and 8.4.6.4

      */

     public boolean overrides(Symbol _other, TypeSymbol origin, Types types, boolean checkResult) {

         return false;

     }

     /** Complete the elaboration of this symbol's definition.

      */

     public void complete() throws CompletionFailure {

         if (completer != null) {

             Completer c = completer;

             completer = null;

             c.complete(this);

         }

     }

     /** True if the symbol represents an entity that exists.

      */

     public boolean exists() {

         return true;

     }

     public Type asType() {

         return type;

     }

     public Symbol getEnclosingElement() {

         return owner;

     }

     public ElementKind getKind() {

         return ElementKind.OTHER;       // most unkind

     }

     public Set<Modifier> getModifiers() {

         return Flags.asModifierSet(flags());

     }

     public Name getSimpleName() {

         return name;

     }

     /**

      * @deprecated this method should never be used by javac internally.

      */

     @Deprecated

     public <A extends java.lang.annotation.Annotation> A getAnnotation(Class<A> annoType) {

         return JavacElements.getAnnotation(this, annoType);

     }

     // TODO: getEnclosedElements should return a javac List, fix in FilteredMemberList

     public java.util.List<Symbol> getEnclosedElements() {

         return List.nil();

     }

     public List<TypeSymbol> getTypeParameters() {

         ListBuffer<TypeSymbol> l = ListBuffer.lb();

         for (Type t : type.getTypeArguments()) {

             l.append(t.tsym);

         }

         return l.toList();

     }

     public static class DelegatedSymbol extends Symbol {

         protected Symbol other;

         public DelegatedSymbol(Symbol other) {

             super(other.kind, other.flags_field, other.name, other.type, other.owner);

             this.other = other;

         }

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

         public Symbol location() { return other.location(); }

         public Symbol location(Type site, Types types) { return other.location(site, types); }

         public Type erasure(Types types) { return other.erasure(types); }

         public Type externalType(Types types) { return other.externalType(types); }

         public boolean isLocal() { return other.isLocal(); }

         public boolean isConstructor() { return other.isConstructor(); }

         public Name getQualifiedName() { return other.getQualifiedName(); }

         public Name flatName() { return other.flatName(); }

         public Scope members() { return other.members(); }

         public boolean isInner() { return other.isInner(); }

         public boolean hasOuterInstance() { return other.hasOuterInstance(); }

         public ClassSymbol enclClass() { return other.enclClass(); }

         public ClassSymbol outermostClass() { return other.outermostClass(); }

         public PackageSymbol packge() { return other.packge(); }

         public boolean isSubClass(Symbol base, Types types) { return other.isSubClass(base, types); }

         public boolean isMemberOf(TypeSymbol clazz, Types types) { return other.isMemberOf(clazz, types); }

         public boolean isEnclosedBy(ClassSymbol clazz) { return other.isEnclosedBy(clazz); }

         public boolean isInheritedIn(Symbol clazz, Types types) { return other.isInheritedIn(clazz, types); }

         public Symbol asMemberOf(Type site, Types types) { return other.asMemberOf(site, types); }

         public void complete() throws CompletionFailure { other.complete(); }

         public <R, P> R accept(ElementVisitor<R, P> v, P p) {

             return other.accept(v, p);

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitSymbol(other, p);

         }

     }

     /** A class for type symbols. Type variables are represented by instances

      *  of this class, classes and packages by instances of subclasses.

      */

     public static class TypeSymbol

             extends Symbol implements TypeParameterElement {

         // Implements TypeParameterElement because type parameters don't

         // have their own TypeSymbol subclass.

         // TODO: type parameters should have their own TypeSymbol subclass

         public TypeSymbol(long flags, Name name, Type type, Symbol owner) {

             super(TYP, flags, name, type, owner);

         }

         /** form a fully qualified name from a name and an owner

          */

         static public Name formFullName(Name name, Symbol owner) {

             if (owner == null) return name;

             if (((owner.kind != ERR)) &&

                 ((owner.kind & (VAR | MTH)) != 0

                  || (owner.kind == TYP && owner.type.tag == TYPEVAR)

                  )) return name;

             Name prefix = owner.getQualifiedName();

             if (prefix == null || prefix == prefix.table.names.empty)

                 return name;

             else return prefix.append('.', name);

         }

         /** form a fully qualified name from a name and an owner, after

          *  converting to flat representation

          */

         static public Name formFlatName(Name name, Symbol owner) {

             if (owner == null ||

                 (owner.kind & (VAR | MTH)) != 0

                 || (owner.kind == TYP && owner.type.tag == TYPEVAR)

                 ) return name;

             char sep = owner.kind == TYP ? '$' : '.';

             Name prefix = owner.flatName();

             if (prefix == null || prefix == prefix.table.names.empty)

                 return name;

             else return prefix.append(sep, name);

         }

         /**

          * A total ordering between type symbols that refines the

          * class inheritance graph.

          *

          * Typevariables always precede other kinds of symbols.

          */

         public final boolean precedes(TypeSymbol that, Types types) {

             if (this == that)

                 return false;

             if (this.type.tag == that.type.tag) {

                 if (this.type.tag == CLASS) {

                     return

                         types.rank(that.type) < types.rank(this.type) ||

                         types.rank(that.type) == types.rank(this.type) &&

                         that.getQualifiedName().compareTo(this.getQualifiedName()) < 0;

                 } else if (this.type.tag == TYPEVAR) {

                     return types.isSubtype(this.type, that.type);

                 }

             }

             return this.type.tag == TYPEVAR;

         }

         // For type params; overridden in subclasses.

         public ElementKind getKind() {

             return ElementKind.TYPE_PARAMETER;

         }

         public java.util.List<Symbol> getEnclosedElements() {

             List<Symbol> list = List.nil();

             if (kind == TYP && type.tag == TYPEVAR) {

                 return list;

             }

             for (Scope.Entry e = members().elems; e != null; e = e.sibling) {

                 if (e.sym != null && (e.sym.flags() & SYNTHETIC) == 0 && e.sym.owner == this)

                     list = list.prepend(e.sym);

             }

             return list;

         }

         // For type params.

         // Perhaps not needed if getEnclosingElement can be spec'ed

         // to do the same thing.

         // TODO: getGenericElement() might not be needed

         public Symbol getGenericElement() {

             return owner;

         }

         public <R, P> R accept(ElementVisitor<R, P> v, P p) {

             assert type.tag == TYPEVAR; // else override will be invoked

             return v.visitTypeParameter(this, p);

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitTypeSymbol(this, p);

         }

         public List<Type> getBounds() {

             TypeVar t = (TypeVar)type;

             Type bound = t.getUpperBound();

             if (!bound.isCompound())

                 return List.of(bound);

             ClassType ct = (ClassType)bound;

             if (!ct.tsym.erasure_field.isInterface()) {

                 return ct.interfaces_field.prepend(ct.supertype_field);

             } else {

                 // No superclass was given in bounds.

                 // In this case, supertype is Object, erasure is first interface.

                 return ct.interfaces_field;

             }

         }

     }

     /** A class for package symbols

      */

     public static class PackageSymbol extends TypeSymbol

         implements PackageElement {

         public Scope members_field;

         public Name fullname;

         public ClassSymbol package_info; // see bug 6443073

         public PackageSymbol(Name name, Type type, Symbol owner) {

             super(0, name, type, owner);

             this.kind = PCK;

             this.members_field = null;

             this.fullname = formFullName(name, owner);

         }

         public PackageSymbol(Name name, Symbol owner) {

             this(name, null, owner);

             this.type = new PackageType(this);

         }

         public String toString() {

             return fullname.toString();

         }

         public Name getQualifiedName() {

             return fullname;

         }

         public boolean isUnnamed() {

             return name.isEmpty() && owner != null;

         }

         public Scope members() {

             if (completer != null) complete();

             return members_field;

         }

         public long flags() {

             if (completer != null) complete();

             return flags_field;

         }

         public List<Attribute.Compound> getAnnotationMirrors() {

             if (completer != null) complete();

             if (package_info != null && package_info.completer != null) {

                 package_info.complete();

                 if (attributes_field.isEmpty())

                     attributes_field = package_info.attributes_field;

             }

             assert attributes_field != null;

             return attributes_field;

         }

         /** A package "exists" if a type or package that exists has

          *  been seen within it.

          */

         public boolean exists() {

             return (flags_field & EXISTS) != 0;

         }

         public ElementKind getKind() {

             return ElementKind.PACKAGE;

         }

         public Symbol getEnclosingElement() {

             return null;

         }

         public <R, P> R accept(ElementVisitor<R, P> v, P p) {

             return v.visitPackage(this, p);

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitPackageSymbol(this, p);

         }

     }

     /** A class for class symbols

      */

     public static class ClassSymbol extends TypeSymbol implements TypeElement {

         /** a scope for all class members; variables, methods and inner classes

          *  type parameters are not part of this scope

          */

         public Scope members_field;

         /** the fully qualified name of the class, i.e. pck.outer.inner.

          *  null for anonymous classes

          */

         public Name fullname;

         /** the fully qualified name of the class after converting to flat

          *  representation, i.e. pck.outer$inner,

          *  set externally for local and anonymous classes

          */

         public Name flatname;

         /** the sourcefile where the class came from

          */

         public JavaFileObject sourcefile;

         /** the classfile from where to load this class

          *  this will have extension .class or .java

          */

         public JavaFileObject classfile;

         /** the constant pool of the class

          */

         public Pool pool;

         public ClassSymbol(long flags, Name name, Type type, Symbol owner) {

             super(flags, name, type, owner);

             this.members_field = null;

             this.fullname = formFullName(name, owner);

             this.flatname = formFlatName(name, owner);

             this.sourcefile = null;

             this.classfile = null;

             this.pool = null;

         }

         public ClassSymbol(long flags, Name name, Symbol owner) {

             this(

                 flags,

                 name,

                 new ClassType(Type.noType, null, null),

                 owner);

             this.type.tsym = this;

         }

         /** The Java source which this symbol represents.

          */

         public String toString() {

             return className();

         }

         public long flags() {

             if (completer != null) complete();

             return flags_field;

         }

         public Scope members() {

             if (completer != null) complete();

             return members_field;

         }

         public List<Attribute.Compound> getAnnotationMirrors() {

             if (completer != null) complete();

             assert attributes_field != null;

             return attributes_field;

         }

         public Type erasure(Types types) {

             if (erasure_field == null)

                 erasure_field = new ClassType(types.erasure(type.getEnclosingType()),

                                               List.<Type>nil(), this);

             return erasure_field;

         }

         public String className() {

             if (name.isEmpty())

                 return

                     Log.getLocalizedString("anonymous.class", flatname);

             else

                 return fullname.toString();

         }

         public Name getQualifiedName() {

             return fullname;

         }

         public Name flatName() {

             return flatname;

         }

         public boolean isSubClass(Symbol base, Types types) {

             if (this == base) {

                 return true;

             } else if ((base.flags() & INTERFACE) != 0) {

                 for (Type t = type; t.tag == CLASS; t = types.supertype(t))

                     for (List<Type> is = types.interfaces(t);

                          is.nonEmpty();

                          is = is.tail)

                         if (is.head.tsym.isSubClass(base, types)) return true;

             } else {

                 for (Type t = type; t.tag == CLASS; t = types.supertype(t))

                     if (t.tsym == base) return true;

             }

             return false;

         }

         /** Complete the elaboration of this symbol's definition.

          */

         public void complete() throws CompletionFailure {

             try {

                 super.complete();

             } catch (CompletionFailure ex) {

                 // quiet error recovery

                 flags_field |= (PUBLIC|STATIC);

                 this.type = new ErrorType(this, Type.noType);

                 throw ex;

             }

         }

         public List<Type> getInterfaces() {

             complete();

             if (type instanceof ClassType) {

                 ClassType t = (ClassType)type;

                 if (t.interfaces_field == null) // FIXME: shouldn't be null

                     t.interfaces_field = List.nil();

                 return t.interfaces_field;

             } else {

                 return List.nil();

             }

         }

         public Type getSuperclass() {

             complete();

             if (type instanceof ClassType) {

                 ClassType t = (ClassType)type;

                 if (t.supertype_field == null) // FIXME: shouldn't be null

                     t.supertype_field = Type.noType;

                 // An interface has no superclass; its supertype is Object.

                 return t.isInterface()

                     ? Type.noType

                     : t.supertype_field;

             } else {

                 return Type.noType;

             }

         }

         public ElementKind getKind() {

             long flags = flags();

             if ((flags & ANNOTATION) != 0)

                 return ElementKind.ANNOTATION_TYPE;

             else if ((flags & INTERFACE) != 0)

                 return ElementKind.INTERFACE;

             else if ((flags & ENUM) != 0)

                 return ElementKind.ENUM;

             else

                 return ElementKind.CLASS;

         }

         public NestingKind getNestingKind() {

             complete();

             if (owner.kind == PCK)

                 return NestingKind.TOP_LEVEL;

             else if (name.isEmpty())

                 return NestingKind.ANONYMOUS;

             else if (owner.kind == MTH)

                 return NestingKind.LOCAL;

             else

                 return NestingKind.MEMBER;

         }

         /**

          * @deprecated this method should never be used by javac internally.

          */

         @Override @Deprecated

         public <A extends java.lang.annotation.Annotation> A getAnnotation(Class<A> annoType) {

             return JavacElements.getAnnotation(this, annoType);

         }

         public <R, P> R accept(ElementVisitor<R, P> v, P p) {

             return v.visitType(this, p);

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitClassSymbol(this, p);

         }

     }

     /** A class for variable symbols

      */

     public static class VarSymbol extends Symbol implements VariableElement {

         /** The variable's declaration position.

          */

         public int pos = Position.NOPOS;

         /** The variable's address. Used for different purposes during

          *  flow analysis, translation and code generation.

          *  Flow analysis:

          *    If this is a blank final or local variable, its sequence number.

          *  Translation:

          *    If this is a private field, its access number.

          *  Code generation:

          *    If this is a local variable, its logical slot number.

          */

         public int adr = -1;

         /** Construct a variable symbol, given its flags, name, type and owner.

          */

         public VarSymbol(long flags, Name name, Type type, Symbol owner) {

             super(VAR, flags, name, type, owner);

         }

         /** Clone this symbol with new owner.

          */

         public VarSymbol clone(Symbol newOwner) {

             VarSymbol v = new VarSymbol(flags_field, name, type, newOwner);

             v.pos = pos;

             v.adr = adr;

             v.data = data;

 //          System.out.println("clone " + v + " in " + newOwner);//DEBUG

             return v;

         }

         public String toString() {

             return name.toString();

         }

         public Symbol asMemberOf(Type site, Types types) {

             return new VarSymbol(flags_field, name, types.memberType(site, this), owner);

         }

         public ElementKind getKind() {

             long flags = flags();

             if ((flags & PARAMETER) != 0) {

                 if (isExceptionParameter())

                     return ElementKind.EXCEPTION_PARAMETER;

                 else

                     return ElementKind.PARAMETER;

             } else if ((flags & ENUM) != 0) {

                 return ElementKind.ENUM_CONSTANT;

             } else if (owner.kind == TYP || owner.kind == ERR) {

                 return ElementKind.FIELD;

             } else {

                 return ElementKind.LOCAL_VARIABLE;

             }

         }

         public <R, P> R accept(ElementVisitor<R, P> v, P p) {

             return v.visitVariable(this, p);

         }

         public Object getConstantValue() { // Mirror API

             return Constants.decode(getConstValue(), type);

         }

         public void setLazyConstValue(final Env<AttrContext> env,

                                       final Log log,

                                       final Attr attr,

                                       final JCTree.JCExpression initializer)

         {

             setData(new Callable<Object>() {

                 public Object call() {

                     JavaFileObject source = log.useSource(env.toplevel.sourcefile);

                     try {

                         Type itype = attr.attribExpr(initializer, env, type);

                         if (itype.constValue() != null)

                             return attr.coerce(itype, type).constValue();

                         else

                             return null;

                     } finally {

                         log.useSource(source);

                     }

                 }

             });

         }

         /**

          * The variable's constant value, if this is a constant.

          * Before the constant value is evaluated, it points to an

          * initalizer environment.  If this is not a constant, it can

          * be used for other stuff.

          */

         private Object data;

         public boolean isExceptionParameter() {

             return data == ElementKind.EXCEPTION_PARAMETER;

         }

         public boolean isResourceVariable() {

             return data == ElementKind.RESOURCE_VARIABLE;

         }

         public Object getConstValue() {

             // TODO: Consider if getConstValue and getConstantValue can be collapsed

             if (data == ElementKind.EXCEPTION_PARAMETER ||

                 data == ElementKind.RESOURCE_VARIABLE) {

                 return null;

             } else if (data instanceof Callable<?>) {

                 // In this case, this is a final variable, with an as

                 // yet unevaluated initializer.

                 Callable<?> eval = (Callable<?>)data;

                 data = null; // to make sure we don't evaluate this twice.

                 try {

                     data = eval.call();

                 } catch (Exception ex) {

                     throw new AssertionError(ex);

                 }

             }

             return data;

         }

         public void setData(Object data) {

             assert !(data instanceof Env<?>) : this;

             this.data = data;

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitVarSymbol(this, p);

         }

     }

     /** A class for method symbols.

      */

     public static class MethodSymbol extends Symbol implements ExecutableElement {

         /** The code of the method. */

         public Code code = null;

         /** The parameters of the method. */

         public List<VarSymbol> params = null;

         /** The names of the parameters */

         public List<Name> savedParameterNames;

         /** For an attribute field accessor, its default value if any.

          *  The value is null if none appeared in the method

          *  declaration.

          */

         public Attribute defaultValue = null;

         /** Construct a method symbol, given its flags, name, type and owner.

          */

         public MethodSymbol(long flags, Name name, Type type, Symbol owner) {

             super(MTH, flags, name, type, owner);

             assert owner.type.tag != TYPEVAR : owner + "." + name;

         }

         /** Clone this symbol with new owner.

          */

         public MethodSymbol clone(Symbol newOwner) {

             MethodSymbol m = new MethodSymbol(flags_field, name, type, newOwner);

             m.code = code;

             return m;

         }

         /** The Java source which this symbol represents.

          */

         public String toString() {

             if ((flags() & BLOCK) != 0) {

                 return owner.name.toString();

             } else {

                 String s = (name == name.table.names.init)

                     ? owner.name.toString()

                     : name.toString();

                 if (type != null) {

                     if (type.tag == FORALL)

                         s = "<" + ((ForAll)type).getTypeArguments() + ">" + s;

                     s += "(" + type.argtypes((flags() & VARARGS) != 0) + ")";

                 }

                 return s;

             }

         }

         /** find a symbol that this (proxy method) symbol implements.

          *  @param    c       The class whose members are searched for

          *                    implementations

          */

         public Symbol implemented(TypeSymbol c, Types types) {

             Symbol impl = null;

             for (List<Type> is = types.interfaces(c.type);

                  impl == null && is.nonEmpty();

                  is = is.tail) {

                 TypeSymbol i = is.head.tsym;

                 for (Scope.Entry e = i.members().lookup(name);

                      impl == null && e.scope != null;

                      e = e.next()) {

                     if (this.overrides(e.sym, (TypeSymbol)owner, types, true) &&

                         // FIXME: I suspect the following requires a

                         // subst() for a parametric return type.

                         types.isSameType(type.getReturnType(),

                                          types.memberType(owner.type, e.sym).getReturnType())) {

                         impl = e.sym;

                     }

                     if (impl == null)

                         impl = implemented(i, types);

                 }

             }

             return impl;

         }

         /** Will the erasure of this method be considered by the VM to

          *  override the erasure of the other when seen from class `origin'?

          */

         public boolean binaryOverrides(Symbol _other, TypeSymbol origin, Types types) {

             if (isConstructor() || _other.kind != MTH) return false;

             if (this == _other) return true;

             MethodSymbol other = (MethodSymbol)_other;

             // check for a direct implementation

             if (other.isOverridableIn((TypeSymbol)owner) &&

                 types.asSuper(owner.type, other.owner) != null &&

                 types.isSameType(erasure(types), other.erasure(types)))

                 return true;

             // check for an inherited implementation

             return

                 (flags() & ABSTRACT) == 0 &&

                 other.isOverridableIn(origin) &&

                 this.isMemberOf(origin, types) &&

                 types.isSameType(erasure(types), other.erasure(types));

         }

         /** The implementation of this (abstract) symbol in class origin,

          *  from the VM's point of view, null if method does not have an

          *  implementation in class.

          *  @param origin   The class of which the implementation is a member.

          */

         public MethodSymbol binaryImplementation(ClassSymbol origin, Types types) {

             for (TypeSymbol c = origin; c != null; c = types.supertype(c.type).tsym) {

                 for (Scope.Entry e = c.members().lookup(name);

                      e.scope != null;

                      e = e.next()) {

                     if (e.sym.kind == MTH &&

                         ((MethodSymbol)e.sym).binaryOverrides(this, origin, types))

                         return (MethodSymbol)e.sym;

                 }

             }

             return null;

         }

         /** Does this symbol override `other' symbol, when both are seen as

          *  members of class `origin'?  It is assumed that _other is a member

          *  of origin.

          *

          *  It is assumed that both symbols have the same name.  The static

          *  modifier is ignored for this test.

          *

          *  See JLS 8.4.6.1 (without transitivity) and 8.4.6.4

          */

         public boolean overrides(Symbol _other, TypeSymbol origin, Types types, boolean checkResult) {

             if (isConstructor() || _other.kind != MTH) return false;

             if (this == _other) return true;

             MethodSymbol other = (MethodSymbol)_other;

             // check for a direct implementation

             if (other.isOverridableIn((TypeSymbol)owner) &&

                 types.asSuper(owner.type, other.owner) != null) {

                 Type mt = types.memberType(owner.type, this);

                 Type ot = types.memberType(owner.type, other);

                 if (types.isSubSignature(mt, ot)) {

                     if (!checkResult)

                         return true;

                     if (types.returnTypeSubstitutable(mt, ot))

                         return true;

                 }

             }

             // check for an inherited implementation

             if ((flags() & ABSTRACT) != 0 ||

                 (other.flags() & ABSTRACT) == 0 ||

                 !other.isOverridableIn(origin) ||

                 !this.isMemberOf(origin, types))

                 return false;

             // assert types.asSuper(origin.type, other.owner) != null;

             Type mt = types.memberType(origin.type, this);

             Type ot = types.memberType(origin.type, other);

             return

                 types.isSubSignature(mt, ot) &&

                 (!checkResult || types.resultSubtype(mt, ot, Warner.noWarnings));

         }

         private boolean isOverridableIn(TypeSymbol origin) {

             // JLS3 8.4.6.1

             switch ((int)(flags_field & Flags.AccessFlags)) {

             case Flags.PRIVATE:

                 return false;

             case Flags.PUBLIC:

                 return true;

             case Flags.PROTECTED:

                 return (origin.flags() & INTERFACE) == 0;

             case 0:

                 // for package private: can only override in the same

                 // package

                 return

                     this.packge() == origin.packge() &&

                     (origin.flags() & INTERFACE) == 0;

             default:

                 return false;

             }

         }

         /** The implementation of this (abstract) symbol in class origin;

          *  null if none exists. Synthetic methods are not considered

          *  as possible implementations.

          */

         public MethodSymbol implementation(TypeSymbol origin, Types types, boolean checkResult) {

             return implementation(origin, types, checkResult, implementation_filter);

         }

         // where

             private static final Filter<Symbol> implementation_filter = new Filter<Symbol>() {

                 public boolean accepts(Symbol s) {

                     return s.kind == Kinds.MTH &&

                             (s.flags() & SYNTHETIC) == 0;

                 }

             };

         public MethodSymbol implementation(TypeSymbol origin, Types types, boolean checkResult, Filter<Symbol> implFilter) {

             MethodSymbol res = types.implementation(this, origin, types, checkResult, implFilter);

             if (res != null)

                 return res;

             // if origin is derived from a raw type, we might have missed

             // an implementation because we do not know enough about instantiations.

             // in this case continue with the supertype as origin.

             if (types.isDerivedRaw(origin.type))

                 return implementation(types.supertype(origin.type).tsym, types, checkResult);

             else

                 return null;

         }

         public List<VarSymbol> params() {

             owner.complete();

             if (params == null) {

                 // If ClassReader.saveParameterNames has been set true, then

                 // savedParameterNames will be set to a list of names that

                 // matches the types in type.getParameterTypes().  If any names

                 // were not found in the class file, those names in the list will

                 // be set to the empty name.

                 // If ClassReader.saveParameterNames has been set false, then

                 // savedParameterNames will be null.

                 List<Name> paramNames = savedParameterNames;

                 savedParameterNames = null;

                 // discard the provided names if the list of names is the wrong size.

                 if (paramNames == null || paramNames.size() != type.getParameterTypes().size())

                     paramNames = List.nil();

                 ListBuffer<VarSymbol> buf = new ListBuffer<VarSymbol>();

                 List<Name> remaining = paramNames;

                 // assert: remaining and paramNames are both empty or both

                 // have same cardinality as type.getParameterTypes()

                 int i = 0;

                 for (Type t : type.getParameterTypes()) {

                     Name paramName;

                     if (remaining.isEmpty()) {

                         // no names for any parameters available

                         paramName = createArgName(i, paramNames);

                     } else {

                         paramName = remaining.head;

                         remaining = remaining.tail;

                         if (paramName.isEmpty()) {

                             // no name for this specific parameter

                             paramName = createArgName(i, paramNames);

                         }

                     }

                     buf.append(new VarSymbol(PARAMETER, paramName, t, this));

                     i++;

                 }

                 params = buf.toList();

             }

             return params;

         }

         // Create a name for the argument at position 'index' that is not in

         // the exclude list. In normal use, either no names will have been

         // provided, in which case the exclude list is empty, or all the names

         // will have been provided, in which case this method will not be called.

         private Name createArgName(int index, List<Name> exclude) {

             String prefix = "arg";

             while (true) {

                 Name argName = name.table.fromString(prefix + index);

                 if (!exclude.contains(argName))

                     return argName;

                 prefix += "$";

             }

         }

         public Symbol asMemberOf(Type site, Types types) {

             return new MethodSymbol(flags_field, name, types.memberType(site, this), owner);

         }

         public ElementKind getKind() {

             if (name == name.table.names.init)

                 return ElementKind.CONSTRUCTOR;

             else if (name == name.table.names.clinit)

                 return ElementKind.STATIC_INIT;

             else

                 return ElementKind.METHOD;

         }

         public Attribute getDefaultValue() {

             return defaultValue;

         }

         public List<VarSymbol> getParameters() {

             return params();

         }

         public boolean isVarArgs() {

             return (flags() & VARARGS) != 0;

         }

         public <R, P> R accept(ElementVisitor<R, P> v, P p) {

             return v.visitExecutable(this, p);

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitMethodSymbol(this, p);

         }

         public Type getReturnType() {

             return asType().getReturnType();

         }

         public List<Type> getThrownTypes() {

             return asType().getThrownTypes();

         }

     }

     /** A class for predefined operators.

      */

     public static class OperatorSymbol extends MethodSymbol {

         public int opcode;

         public OperatorSymbol(Name name, Type type, int opcode, Symbol owner) {

             super(PUBLIC | STATIC, name, type, owner);

             this.opcode = opcode;

         }

         public <R, P> R accept(Symbol.Visitor<R, P> v, P p) {

             return v.visitOperatorSymbol(this, p);

         }

     }

     /** Symbol completer interface.

      */

     public static interface Completer {

         void complete(Symbol sym) throws CompletionFailure;

     }

     public static class CompletionFailure extends RuntimeException {

         private static final long serialVersionUID = 0;

         public Symbol sym;

         /** A diagnostic object describing the failure

          */

         public JCDiagnostic diag;

         /** A localized string describing the failure.

          * @deprecated Use {@code getDetail()} or {@code getMessage()}

          */

         @Deprecated

         public String errmsg;

         public CompletionFailure(Symbol sym, String errmsg) {

             this.sym = sym;

             this.errmsg = errmsg;

 //          this.printStackTrace();//DEBUG

         }

         public CompletionFailure(Symbol sym, JCDiagnostic diag) {

             this.sym = sym;

             this.diag = diag;

 //          this.printStackTrace();//DEBUG

         }

         public JCDiagnostic getDiagnostic() {

             return diag;

         }

         @Override

         public String getMessage() {

             if (diag != null)

                 return diag.getMessage(null);

             else

                 return errmsg;

         }

         public Object getDetailValue() {

             return (diag != null ? diag : errmsg);

         }

         @Override

         public CompletionFailure initCause(Throwable cause) {

             super.initCause(cause);

             return this;

         }

     }

     /**

      * A visitor for symbols.  A visitor is used to implement operations

      * (or relations) on symbols.  Most common operations on types are

      * binary relations and this interface is designed for binary

      * relations, that is, operations on the form

      * Symbol × P → R.

      * <!-- In plain text: Type x P -> R -->

      *

      * @param <R> the return type of the operation implemented by this

      * visitor; use Void if no return type is needed.

      * @param <P> 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 interface Visitor<R,P> {

         R visitClassSymbol(ClassSymbol s, P arg);

         R visitMethodSymbol(MethodSymbol s, P arg);

         R visitPackageSymbol(PackageSymbol s, P arg);

         R visitOperatorSymbol(OperatorSymbol s, P arg);

         R visitVarSymbol(VarSymbol s, P arg);

         R visitTypeSymbol(TypeSymbol s, P arg);

         R visitSymbol(Symbol s, P arg);

     }

 }