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

 /*

  * Copyright 1999-2008 Sun Microsystems, Inc.  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.  Sun designates this

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

  * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

  * have any questions.

  */

 package com.sun.tools.javac.comp;

 import java.util.*;

 import java.util.Set;

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

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

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

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

 import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;

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

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

 import com.sun.tools.javac.code.Lint;

 import com.sun.tools.javac.code.Lint.LintCategory;

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

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

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

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

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

 /** Type checking helper class for the attribution phase.

  *

  *  <p><b>This is NOT part of any API supported by Sun Microsystems.  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 Check {

     protected static final Context.Key<Check> checkKey =

         new Context.Key<Check>();

     private final Name.Table names;

     private final Log log;

     private final Symtab syms;

     private final Infer infer;

     private final Target target;

     private final Source source;

     private final Types types;

     private final boolean skipAnnotations;

     private final TreeInfo treeinfo;

     // The set of lint options currently in effect. It is initialized

     // from the context, and then is set/reset as needed by Attr as it

     // visits all the various parts of the trees during attribution.

     private Lint lint;

     public static Check instance(Context context) {

         Check instance = context.get(checkKey);

         if (instance == null)

             instance = new Check(context);

         return instance;

     }

     protected Check(Context context) {

         context.put(checkKey, this);

         names = Name.Table.instance(context);

         log = Log.instance(context);

         syms = Symtab.instance(context);

         infer = Infer.instance(context);

         this.types = Types.instance(context);

         Options options = Options.instance(context);

         target = Target.instance(context);

         source = Source.instance(context);

         lint = Lint.instance(context);

         treeinfo = TreeInfo.instance(context);

         Source source = Source.instance(context);

         allowGenerics = source.allowGenerics();

         allowAnnotations = source.allowAnnotations();

         complexInference = options.get("-complexinference") != null;

         skipAnnotations = options.get("skipAnnotations") != null;

         boolean verboseDeprecated = lint.isEnabled(LintCategory.DEPRECATION);

         boolean verboseUnchecked = lint.isEnabled(LintCategory.UNCHECKED);

         deprecationHandler = new MandatoryWarningHandler(log,verboseDeprecated, "deprecated");

         uncheckedHandler = new MandatoryWarningHandler(log, verboseUnchecked, "unchecked");

     }

     /** Switch: generics enabled?

      */

     boolean allowGenerics;

     /** Switch: annotations enabled?

      */

     boolean allowAnnotations;

     /** Switch: -complexinference option set?

      */

     boolean complexInference;

     /** A table mapping flat names of all compiled classes in this run to their

      *  symbols; maintained from outside.

      */

     public Map<Name,ClassSymbol> compiled = new HashMap<Name, ClassSymbol>();

     /** A handler for messages about deprecated usage.

      */

     private MandatoryWarningHandler deprecationHandler;

     /** A handler for messages about unchecked or unsafe usage.

      */

     private MandatoryWarningHandler uncheckedHandler;

 /* *************************************************************************

  * Errors and Warnings

  **************************************************************************/

     Lint setLint(Lint newLint) {

         Lint prev = lint;

         lint = newLint;

         return prev;

     }

     /** Warn about deprecated symbol.

      *  @param pos        Position to be used for error reporting.

      *  @param sym        The deprecated symbol.

      */

     void warnDeprecated(DiagnosticPosition pos, Symbol sym) {

         if (!lint.isSuppressed(LintCategory.DEPRECATION))

             deprecationHandler.report(pos, "has.been.deprecated", sym, sym.location());

     }

     /** Warn about unchecked operation.

      *  @param pos        Position to be used for error reporting.

      *  @param msg        A string describing the problem.

      */

     public void warnUnchecked(DiagnosticPosition pos, String msg, Object... args) {

         if (!lint.isSuppressed(LintCategory.UNCHECKED))

             uncheckedHandler.report(pos, msg, args);

     }

     /**

      * Report any deferred diagnostics.

      */

     public void reportDeferredDiagnostics() {

         deprecationHandler.reportDeferredDiagnostic();

         uncheckedHandler.reportDeferredDiagnostic();

     }

     /** Report a failure to complete a class.

      *  @param pos        Position to be used for error reporting.

      *  @param ex         The failure to report.

      */

     public Type completionError(DiagnosticPosition pos, CompletionFailure ex) {

         log.error(pos, "cant.access", ex.sym, ex.getDetailValue());

         if (ex instanceof ClassReader.BadClassFile) throw new Abort();

         else return syms.errType;

     }

     /** Report a type error.

      *  @param pos        Position to be used for error reporting.

      *  @param problem    A string describing the error.

      *  @param found      The type that was found.

      *  @param req        The type that was required.

      */

     Type typeError(DiagnosticPosition pos, Object problem, Type found, Type req) {

         log.error(pos, "prob.found.req",

                   problem, found, req);

         return syms.errType;

     }

     Type typeError(DiagnosticPosition pos, String problem, Type found, Type req, Object explanation) {

         log.error(pos, "prob.found.req.1", problem, found, req, explanation);

         return syms.errType;

     }

     /** Report an error that wrong type tag was found.

      *  @param pos        Position to be used for error reporting.

      *  @param required   An internationalized string describing the type tag

      *                    required.

      *  @param found      The type that was found.

      */

     Type typeTagError(DiagnosticPosition pos, Object required, Object found) {

         log.error(pos, "type.found.req", found, required);

         return syms.errType;

     }

     /** Report an error that symbol cannot be referenced before super

      *  has been called.

      *  @param pos        Position to be used for error reporting.

      *  @param sym        The referenced symbol.

      */

     void earlyRefError(DiagnosticPosition pos, Symbol sym) {

         log.error(pos, "cant.ref.before.ctor.called", sym);

     }

     /** Report duplicate declaration error.

      */

     void duplicateError(DiagnosticPosition pos, Symbol sym) {

         if (!sym.type.isErroneous()) {

             log.error(pos, "already.defined", sym, sym.location());

         }

     }

     /** Report array/varargs duplicate declaration

      */

     void varargsDuplicateError(DiagnosticPosition pos, Symbol sym1, Symbol sym2) {

         if (!sym1.type.isErroneous() && !sym2.type.isErroneous()) {

             log.error(pos, "array.and.varargs", sym1, sym2, sym2.location());

         }

     }

 /* ************************************************************************

  * duplicate declaration checking

  *************************************************************************/

     /** Check that variable does not hide variable with same name in

      *  immediately enclosing local scope.

      *  @param pos           Position for error reporting.

      *  @param v             The symbol.

      *  @param s             The scope.

      */

     void checkTransparentVar(DiagnosticPosition pos, VarSymbol v, Scope s) {

         if (s.next != null) {

             for (Scope.Entry e = s.next.lookup(v.name);

                  e.scope != null && e.sym.owner == v.owner;

                  e = e.next()) {

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

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

                     v.name != names.error) {

                     duplicateError(pos, e.sym);

                     return;

                 }

             }

         }

     }

     /** Check that a class or interface does not hide a class or

      *  interface with same name in immediately enclosing local scope.

      *  @param pos           Position for error reporting.

      *  @param c             The symbol.

      *  @param s             The scope.

      */

     void checkTransparentClass(DiagnosticPosition pos, ClassSymbol c, Scope s) {

         if (s.next != null) {

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

                  e.scope != null && e.sym.owner == c.owner;

                  e = e.next()) {

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

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

                     c.name != names.error) {

                     duplicateError(pos, e.sym);

                     return;

                 }

             }

         }

     }

     /** Check that class does not have the same name as one of

      *  its enclosing classes, or as a class defined in its enclosing scope.

      *  return true if class is unique in its enclosing scope.

      *  @param pos           Position for error reporting.

      *  @param name          The class name.

      *  @param s             The enclosing scope.

      */

     boolean checkUniqueClassName(DiagnosticPosition pos, Name name, Scope s) {

         for (Scope.Entry e = s.lookup(name); e.scope == s; e = e.next()) {

             if (e.sym.kind == TYP && e.sym.name != names.error) {

                 duplicateError(pos, e.sym);

                 return false;

             }

         }

         for (Symbol sym = s.owner; sym != null; sym = sym.owner) {

             if (sym.kind == TYP && sym.name == name && sym.name != names.error) {

                 duplicateError(pos, sym);

                 return true;

             }

         }

         return true;

     }

 /* *************************************************************************

  * Class name generation

  **************************************************************************/

     /** Return name of local class.

      *  This is of the form    <enclClass> $ n <classname>

      *  where

      *    enclClass is the flat name of the enclosing class,

      *    classname is the simple name of the local class

      */

     Name localClassName(ClassSymbol c) {

         for (int i=1; ; i++) {

             Name flatname = names.

                 fromString("" + c.owner.enclClass().flatname +

                            target.syntheticNameChar() + i +

                            c.name);

             if (compiled.get(flatname) == null) return flatname;

         }

     }

 /* *************************************************************************

  * Type Checking

  **************************************************************************/

     /** Check that a given type is assignable to a given proto-type.

      *  If it is, return the type, otherwise return errType.

      *  @param pos        Position to be used for error reporting.

      *  @param found      The type that was found.

      *  @param req        The type that was required.

      */

     Type checkType(DiagnosticPosition pos, Type found, Type req) {

         if (req.tag == ERROR)

             return req;

         if (found.tag == FORALL)

             return instantiatePoly(pos, (ForAll)found, req, convertWarner(pos, found, req));

         if (req.tag == NONE)

             return found;

         if (types.isAssignable(found, req, convertWarner(pos, found, req)))

             return found;

         if (found.tag <= DOUBLE && req.tag <= DOUBLE)

             return typeError(pos, JCDiagnostic.fragment("possible.loss.of.precision"), found, req);

         if (found.isSuperBound()) {

             log.error(pos, "assignment.from.super-bound", found);

             return syms.errType;

         }

         if (req.isExtendsBound()) {

             log.error(pos, "assignment.to.extends-bound", req);

             return syms.errType;

         }

         return typeError(pos, JCDiagnostic.fragment("incompatible.types"), found, req);

     }

     /** Instantiate polymorphic type to some prototype, unless

      *  prototype is `anyPoly' in which case polymorphic type

      *  is returned unchanged.

      */

     Type instantiatePoly(DiagnosticPosition pos, ForAll t, Type pt, Warner warn) {

         if (pt == Infer.anyPoly && complexInference) {

             return t;

         } else if (pt == Infer.anyPoly || pt.tag == NONE) {

             Type newpt = t.qtype.tag <= VOID ? t.qtype : syms.objectType;

             return instantiatePoly(pos, t, newpt, warn);

         } else if (pt.tag == ERROR) {

             return pt;

         } else {

             try {

                 return infer.instantiateExpr(t, pt, warn);

             } catch (Infer.NoInstanceException ex) {

                 if (ex.isAmbiguous) {

                     JCDiagnostic d = ex.getDiagnostic();

                     log.error(pos,

                               "undetermined.type" + (d!=null ? ".1" : ""),

                               t, d);

                     return syms.errType;

                 } else {

                     JCDiagnostic d = ex.getDiagnostic();

                     return typeError(pos,

                                      JCDiagnostic.fragment("incompatible.types" + (d!=null ? ".1" : ""), d),

                                      t, pt);

                 }

             }

         }

     }

     /** Check that a given type can be cast to a given target type.

      *  Return the result of the cast.

      *  @param pos        Position to be used for error reporting.

      *  @param found      The type that is being cast.

      *  @param req        The target type of the cast.

      */

     Type checkCastable(DiagnosticPosition pos, Type found, Type req) {

         if (found.tag == FORALL) {

             instantiatePoly(pos, (ForAll) found, req, castWarner(pos, found, req));

             return req;

         } else if (types.isCastable(found, req, castWarner(pos, found, req))) {

             return req;

         } else {

             return typeError(pos,

                              JCDiagnostic.fragment("inconvertible.types"),

                              found, req);

         }

     }

 //where

         /** Is type a type variable, or a (possibly multi-dimensional) array of

          *  type variables?

          */

         boolean isTypeVar(Type t) {

             return t.tag == TYPEVAR || t.tag == ARRAY && isTypeVar(types.elemtype(t));

         }

     /** Check that a type is within some bounds.

      *

      *  Used in TypeApply to verify that, e.g., X in V<X> is a valid

      *  type argument.

      *  @param pos           Position to be used for error reporting.

      *  @param a             The type that should be bounded by bs.

      *  @param bs            The bound.

      */

     private void checkExtends(DiagnosticPosition pos, Type a, TypeVar bs) {

         if (a.isUnbound()) {

             return;

         } else if (a.tag != WILDCARD) {

             a = types.upperBound(a);

             for (List<Type> l = types.getBounds(bs); l.nonEmpty(); l = l.tail) {

                 if (!types.isSubtype(a, l.head)) {

                     log.error(pos, "not.within.bounds", a);

                     return;

                 }

             }

         } else if (a.isExtendsBound()) {

             if (!types.isCastable(bs.getUpperBound(), types.upperBound(a), Warner.noWarnings))

                 log.error(pos, "not.within.bounds", a);

         } else if (a.isSuperBound()) {

             if (types.notSoftSubtype(types.lowerBound(a), bs.getUpperBound()))

                 log.error(pos, "not.within.bounds", a);

         }

     }

     /** Check that type is different from 'void'.

      *  @param pos           Position to be used for error reporting.

      *  @param t             The type to be checked.

      */

     Type checkNonVoid(DiagnosticPosition pos, Type t) {

         if (t.tag == VOID) {

             log.error(pos, "void.not.allowed.here");

             return syms.errType;

         } else {

             return t;

         }

     }

     /** Check that type is a class or interface type.

      *  @param pos           Position to be used for error reporting.

      *  @param t             The type to be checked.

      */

     Type checkClassType(DiagnosticPosition pos, Type t) {

         if (t.tag != CLASS && t.tag != ERROR)

             return typeTagError(pos,

                                 JCDiagnostic.fragment("type.req.class"),

                                 (t.tag == TYPEVAR)

                                 ? JCDiagnostic.fragment("type.parameter", t)

                                 : t);

         else

             return t;

     }

     /** Check that type is a class or interface type.

      *  @param pos           Position to be used for error reporting.

      *  @param t             The type to be checked.

      *  @param noBounds    True if type bounds are illegal here.

      */

     Type checkClassType(DiagnosticPosition pos, Type t, boolean noBounds) {

         t = checkClassType(pos, t);

         if (noBounds && t.isParameterized()) {

             List<Type> args = t.getTypeArguments();

             while (args.nonEmpty()) {

                 if (args.head.tag == WILDCARD)

                     return typeTagError(pos,

                                         log.getLocalizedString("type.req.exact"),

                                         args.head);

                 args = args.tail;

             }

         }

         return t;

     }

     /** Check that type is a reifiable class, interface or array type.

      *  @param pos           Position to be used for error reporting.

      *  @param t             The type to be checked.

      */

     Type checkReifiableReferenceType(DiagnosticPosition pos, Type t) {

         if (t.tag != CLASS && t.tag != ARRAY && t.tag != ERROR) {

             return typeTagError(pos,

                                 JCDiagnostic.fragment("type.req.class.array"),

                                 t);

         } else if (!types.isReifiable(t)) {

             log.error(pos, "illegal.generic.type.for.instof");

             return syms.errType;

         } else {

             return t;

         }

     }

     /** Check that type is a reference type, i.e. a class, interface or array type

      *  or a type variable.

      *  @param pos           Position to be used for error reporting.

      *  @param t             The type to be checked.

      */

     Type checkRefType(DiagnosticPosition pos, Type t) {

         switch (t.tag) {

         case CLASS:

         case ARRAY:

         case TYPEVAR:

         case WILDCARD:

         case ERROR:

             return t;

         default:

             return typeTagError(pos,

                                 JCDiagnostic.fragment("type.req.ref"),

                                 t);

         }

     }

     /** Check that type is a null or reference type.

      *  @param pos           Position to be used for error reporting.

      *  @param t             The type to be checked.

      */

     Type checkNullOrRefType(DiagnosticPosition pos, Type t) {

         switch (t.tag) {

         case CLASS:

         case ARRAY:

         case TYPEVAR:

         case WILDCARD:

         case BOT:

         case ERROR:

             return t;

         default:

             return typeTagError(pos,

                                 JCDiagnostic.fragment("type.req.ref"),

                                 t);

         }

     }

     /** Check that flag set does not contain elements of two conflicting sets. s

      *  Return true if it doesn't.

      *  @param pos           Position to be used for error reporting.

      *  @param flags         The set of flags to be checked.

      *  @param set1          Conflicting flags set #1.

      *  @param set2          Conflicting flags set #2.

      */

     boolean checkDisjoint(DiagnosticPosition pos, long flags, long set1, long set2) {

         if ((flags & set1) != 0 && (flags & set2) != 0) {

             log.error(pos,

                       "illegal.combination.of.modifiers",

                       TreeInfo.flagNames(TreeInfo.firstFlag(flags & set1)),

                       TreeInfo.flagNames(TreeInfo.firstFlag(flags & set2)));

             return false;

         } else

             return true;

     }

     /** Check that given modifiers are legal for given symbol and

      *  return modifiers together with any implicit modififiers for that symbol.

      *  Warning: we can't use flags() here since this method

      *  is called during class enter, when flags() would cause a premature

      *  completion.

      *  @param pos           Position to be used for error reporting.

      *  @param flags         The set of modifiers given in a definition.

      *  @param sym           The defined symbol.

      */

     long checkFlags(DiagnosticPosition pos, long flags, Symbol sym, JCTree tree) {

         long mask;

         long implicit = 0;

         switch (sym.kind) {

         case VAR:

             if (sym.owner.kind != TYP)

                 mask = LocalVarFlags;

             else if ((sym.owner.flags_field & INTERFACE) != 0)

                 mask = implicit = InterfaceVarFlags;

             else

                 mask = VarFlags;

             break;

         case MTH:

             if (sym.name == names.init) {

                 if ((sym.owner.flags_field & ENUM) != 0) {

                     // enum constructors cannot be declared public or

                     // protected and must be implicitly or explicitly

                     // private

                     implicit = PRIVATE;

                     mask = PRIVATE;

                 } else

                     mask = ConstructorFlags;

             }  else if ((sym.owner.flags_field & INTERFACE) != 0)

                 mask = implicit = InterfaceMethodFlags;

             else {

                 mask = MethodFlags;

             }

             // Imply STRICTFP if owner has STRICTFP set.

             if (((flags|implicit) & Flags.ABSTRACT) == 0)

               implicit |= sym.owner.flags_field & STRICTFP;

             break;

         case TYP:

             if (sym.isLocal()) {

                 mask = LocalClassFlags;

                 if (sym.name.len == 0) { // Anonymous class

                     // Anonymous classes in static methods are themselves static;

                     // that's why we admit STATIC here.

                     mask |= STATIC;

                     // JLS: Anonymous classes are final.

                     implicit |= FINAL;

                 }

                 if ((sym.owner.flags_field & STATIC) == 0 &&

                     (flags & ENUM) != 0)

                     log.error(pos, "enums.must.be.static");

             } else if (sym.owner.kind == TYP) {

                 mask = MemberClassFlags;

                 if (sym.owner.owner.kind == PCK ||

                     (sym.owner.flags_field & STATIC) != 0)

                     mask |= STATIC;

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

                     log.error(pos, "enums.must.be.static");

                 // Nested interfaces and enums are always STATIC (Spec ???)

                 if ((flags & (INTERFACE | ENUM)) != 0 ) implicit = STATIC;

             } else {

                 mask = ClassFlags;

             }

             // Interfaces are always ABSTRACT

             if ((flags & INTERFACE) != 0) implicit |= ABSTRACT;

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

                 // enums can't be declared abstract or final

                 mask &= ~(ABSTRACT | FINAL);

                 implicit |= implicitEnumFinalFlag(tree);

             }

             // Imply STRICTFP if owner has STRICTFP set.

             implicit |= sym.owner.flags_field & STRICTFP;

             break;

         default:

             throw new AssertionError();

         }

         long illegal = flags & StandardFlags & ~mask;

         if (illegal != 0) {

             if ((illegal & INTERFACE) != 0) {

                 log.error(pos, "intf.not.allowed.here");

                 mask |= INTERFACE;

             }

             else {

                 log.error(pos,

                           "mod.not.allowed.here", TreeInfo.flagNames(illegal));

             }

         }

         else if ((sym.kind == TYP ||

                   // ISSUE: Disallowing abstract&private is no longer appropriate

                   // in the presence of inner classes. Should it be deleted here?

                   checkDisjoint(pos, flags,

                                 ABSTRACT,

                                 PRIVATE | STATIC))

                  &&

                  checkDisjoint(pos, flags,

                                ABSTRACT | INTERFACE,

                                FINAL | NATIVE | SYNCHRONIZED)

                  &&

                  checkDisjoint(pos, flags,

                                PUBLIC,

                                PRIVATE | PROTECTED)

                  &&

                  checkDisjoint(pos, flags,

                                PRIVATE,

                                PUBLIC | PROTECTED)

                  &&

                  checkDisjoint(pos, flags,

                                FINAL,

                                VOLATILE)

                  &&

                  (sym.kind == TYP ||

                   checkDisjoint(pos, flags,

                                 ABSTRACT | NATIVE,

                                 STRICTFP))) {

             // skip

         }

         return flags & (mask | ~StandardFlags) | implicit;

     }

     /** Determine if this enum should be implicitly final.

      *

      *  If the enum has no specialized enum contants, it is final.

      *

      *  If the enum does have specialized enum contants, it is

      *  <i>not</i> final.

      */

     private long implicitEnumFinalFlag(JCTree tree) {

         if (tree.getTag() != JCTree.CLASSDEF) return 0;

         class SpecialTreeVisitor extends JCTree.Visitor {

             boolean specialized;

             SpecialTreeVisitor() {

                 this.specialized = false;

             };

             public void visitTree(JCTree tree) { /* no-op */ }

             public void visitVarDef(JCVariableDecl tree) {

                 if ((tree.mods.flags & ENUM) != 0) {

                     if (tree.init instanceof JCNewClass &&

                         ((JCNewClass) tree.init).def != null) {

                         specialized = true;

                     }

                 }

             }

         }

         SpecialTreeVisitor sts = new SpecialTreeVisitor();

         JCClassDecl cdef = (JCClassDecl) tree;

         for (JCTree defs: cdef.defs) {

             defs.accept(sts);

             if (sts.specialized) return 0;

         }

         return FINAL;

     }

 /* *************************************************************************

  * Type Validation

  **************************************************************************/

     /** Validate a type expression. That is,

      *  check that all type arguments of a parametric type are within

      *  their bounds. This must be done in a second phase after type attributon

      *  since a class might have a subclass as type parameter bound. E.g:

      *

      *  class B<A extends C> { ... }

      *  class C extends B<C> { ... }

      *

      *  and we can't make sure that the bound is already attributed because

      *  of possible cycles.

      */

     private Validator validator = new Validator();

     /** Visitor method: Validate a type expression, if it is not null, catching

      *  and reporting any completion failures.

      */

     void validate(JCTree tree) {

         try {

             if (tree != null) tree.accept(validator);

         } catch (CompletionFailure ex) {

             completionError(tree.pos(), ex);

         }

     }

     /** Visitor method: Validate a list of type expressions.

      */

     void validate(List<? extends JCTree> trees) {

         for (List<? extends JCTree> l = trees; l.nonEmpty(); l = l.tail)

             validate(l.head);

     }

     /** Visitor method: Validate a list of type parameters.

      */

     void validateTypeParams(List<JCTypeParameter> trees) {

         for (List<JCTypeParameter> l = trees; l.nonEmpty(); l = l.tail)

             validate(l.head);

     }

     /** A visitor class for type validation.

      */

     class Validator extends JCTree.Visitor {

         public void visitTypeArray(JCArrayTypeTree tree) {

             validate(tree.elemtype);

         }

         public void visitTypeApply(JCTypeApply tree) {

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

                 List<Type> formals = tree.type.tsym.type.getTypeArguments();

                 List<Type> actuals = tree.type.getTypeArguments();

                 List<JCExpression> args = tree.arguments;

                 List<Type> forms = formals;

                 ListBuffer<TypeVar> tvars_buf = new ListBuffer<TypeVar>();

                 // For matching pairs of actual argument types `a' and

                 // formal type parameters with declared bound `b' ...

                 while (args.nonEmpty() && forms.nonEmpty()) {

                     validate(args.head);

                     // exact type arguments needs to know their

                     // bounds (for upper and lower bound

                     // calculations).  So we create new TypeVars with

                     // bounds substed with actuals.

                     tvars_buf.append(types.substBound(((TypeVar)forms.head),

                                                       formals,

                                                       Type.removeBounds(actuals)));

                     args = args.tail;

                     forms = forms.tail;

                 }

                 args = tree.arguments;

                 List<TypeVar> tvars = tvars_buf.toList();

                 while (args.nonEmpty() && tvars.nonEmpty()) {

                     // Let the actual arguments know their bound

                     args.head.type.withTypeVar(tvars.head);

                     args = args.tail;

                     tvars = tvars.tail;

                 }

                 args = tree.arguments;

                 tvars = tvars_buf.toList();

                 while (args.nonEmpty() && tvars.nonEmpty()) {

                     checkExtends(args.head.pos(),

                                  args.head.type,

                                  tvars.head);

                     args = args.tail;

                     tvars = tvars.tail;

                 }

                 // Check that this type is either fully parameterized, or

                 // not parameterized at all.

                 if (tree.type.getEnclosingType().isRaw())

                     log.error(tree.pos(), "improperly.formed.type.inner.raw.param");

                 if (tree.clazz.getTag() == JCTree.SELECT)

                     visitSelectInternal((JCFieldAccess)tree.clazz);

             }

         }

         public void visitTypeParameter(JCTypeParameter tree) {

             validate(tree.bounds);

             checkClassBounds(tree.pos(), tree.type);

         }

         @Override

         public void visitWildcard(JCWildcard tree) {

             if (tree.inner != null)

                 validate(tree.inner);

         }

         public void visitSelect(JCFieldAccess tree) {

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

                 visitSelectInternal(tree);

                 // Check that this type is either fully parameterized, or

                 // not parameterized at all.

                 if (tree.selected.type.isParameterized() && tree.type.tsym.type.getTypeArguments().nonEmpty())

                     log.error(tree.pos(), "improperly.formed.type.param.missing");

             }

         }

         public void visitSelectInternal(JCFieldAccess tree) {

             if (tree.type.getEnclosingType().tag != CLASS &&

                 tree.selected.type.isParameterized()) {

                 // The enclosing type is not a class, so we are

                 // looking at a static member type.  However, the

                 // qualifying expression is parameterized.

                 log.error(tree.pos(), "cant.select.static.class.from.param.type");

             } else {

                 // otherwise validate the rest of the expression

                 validate(tree.selected);

             }

         }

         /** Default visitor method: do nothing.

          */

         public void visitTree(JCTree tree) {

         }

     }

 /* *************************************************************************

  * Exception checking

  **************************************************************************/

     /* The following methods treat classes as sets that contain

      * the class itself and all their subclasses

      */

     /** Is given type a subtype of some of the types in given list?

      */

     boolean subset(Type t, List<Type> ts) {

         for (List<Type> l = ts; l.nonEmpty(); l = l.tail)

             if (types.isSubtype(t, l.head)) return true;

         return false;

     }

     /** Is given type a subtype or supertype of

      *  some of the types in given list?

      */

     boolean intersects(Type t, List<Type> ts) {

         for (List<Type> l = ts; l.nonEmpty(); l = l.tail)

             if (types.isSubtype(t, l.head) || types.isSubtype(l.head, t)) return true;

         return false;

     }

     /** Add type set to given type list, unless it is a subclass of some class

      *  in the list.

      */

     List<Type> incl(Type t, List<Type> ts) {

         return subset(t, ts) ? ts : excl(t, ts).prepend(t);

     }

     /** Remove type set from type set list.

      */

     List<Type> excl(Type t, List<Type> ts) {

         if (ts.isEmpty()) {

             return ts;

         } else {

             List<Type> ts1 = excl(t, ts.tail);

             if (types.isSubtype(ts.head, t)) return ts1;

             else if (ts1 == ts.tail) return ts;

             else return ts1.prepend(ts.head);

         }

     }

     /** Form the union of two type set lists.

      */

     List<Type> union(List<Type> ts1, List<Type> ts2) {

         List<Type> ts = ts1;

         for (List<Type> l = ts2; l.nonEmpty(); l = l.tail)

             ts = incl(l.head, ts);

         return ts;

     }

     /** Form the difference of two type lists.

      */

     List<Type> diff(List<Type> ts1, List<Type> ts2) {

         List<Type> ts = ts1;

         for (List<Type> l = ts2; l.nonEmpty(); l = l.tail)

             ts = excl(l.head, ts);

         return ts;

     }

     /** Form the intersection of two type lists.

      */

     public List<Type> intersect(List<Type> ts1, List<Type> ts2) {

         List<Type> ts = List.nil();

         for (List<Type> l = ts1; l.nonEmpty(); l = l.tail)

             if (subset(l.head, ts2)) ts = incl(l.head, ts);

         for (List<Type> l = ts2; l.nonEmpty(); l = l.tail)

             if (subset(l.head, ts1)) ts = incl(l.head, ts);

         return ts;

     }

     /** Is exc an exception symbol that need not be declared?

      */

     boolean isUnchecked(ClassSymbol exc) {

         return

             exc.kind == ERR ||

             exc.isSubClass(syms.errorType.tsym, types) ||

             exc.isSubClass(syms.runtimeExceptionType.tsym, types);

     }

     /** Is exc an exception type that need not be declared?

      */

     boolean isUnchecked(Type exc) {

         return

             (exc.tag == TYPEVAR) ? isUnchecked(types.supertype(exc)) :

             (exc.tag == CLASS) ? isUnchecked((ClassSymbol)exc.tsym) :

             exc.tag == BOT;

     }

     /** Same, but handling completion failures.

      */

     boolean isUnchecked(DiagnosticPosition pos, Type exc) {

         try {

             return isUnchecked(exc);

         } catch (CompletionFailure ex) {

             completionError(pos, ex);

             return true;

         }

     }

     /** Is exc handled by given exception list?

      */

     boolean isHandled(Type exc, List<Type> handled) {

         return isUnchecked(exc) || subset(exc, handled);

     }

     /** Return all exceptions in thrown list that are not in handled list.

      *  @param thrown     The list of thrown exceptions.

      *  @param handled    The list of handled exceptions.

      */

     List<Type> unHandled(List<Type> thrown, List<Type> handled) {

         List<Type> unhandled = List.nil();

         for (List<Type> l = thrown; l.nonEmpty(); l = l.tail)

             if (!isHandled(l.head, handled)) unhandled = unhandled.prepend(l.head);

         return unhandled;

     }

 /* *************************************************************************

  * Overriding/Implementation checking

  **************************************************************************/

     /** The level of access protection given by a flag set,

      *  where PRIVATE is highest and PUBLIC is lowest.

      */

     static int protection(long flags) {

         switch ((short)(flags & AccessFlags)) {

         case PRIVATE: return 3;

         case PROTECTED: return 1;

         default:

         case PUBLIC: return 0;

         case 0: return 2;

         }

     }

     /** A string describing the access permission given by a flag set.

      *  This always returns a space-separated list of Java Keywords.

      */

     private static String protectionString(long flags) {

         long flags1 = flags & AccessFlags;

         return (flags1 == 0) ? "package" : TreeInfo.flagNames(flags1);

     }

     /** A customized "cannot override" error message.

      *  @param m      The overriding method.

      *  @param other  The overridden method.

      *  @return       An internationalized string.

      */

     static Object cannotOverride(MethodSymbol m, MethodSymbol other) {

         String key;

         if ((other.owner.flags() & INTERFACE) == 0)

             key = "cant.override";

         else if ((m.owner.flags() & INTERFACE) == 0)

             key = "cant.implement";

         else

             key = "clashes.with";

         return JCDiagnostic.fragment(key, m, m.location(), other, other.location());

     }

     /** A customized "override" warning message.

      *  @param m      The overriding method.

      *  @param other  The overridden method.

      *  @return       An internationalized string.

      */

     static Object uncheckedOverrides(MethodSymbol m, MethodSymbol other) {

         String key;

         if ((other.owner.flags() & INTERFACE) == 0)

             key = "unchecked.override";

         else if ((m.owner.flags() & INTERFACE) == 0)

             key = "unchecked.implement";

         else

             key = "unchecked.clash.with";

         return JCDiagnostic.fragment(key, m, m.location(), other, other.location());

     }

     /** A customized "override" warning message.

      *  @param m      The overriding method.

      *  @param other  The overridden method.

      *  @return       An internationalized string.

      */

     static Object varargsOverrides(MethodSymbol m, MethodSymbol other) {

         String key;

         if ((other.owner.flags() & INTERFACE) == 0)

             key = "varargs.override";

         else  if ((m.owner.flags() & INTERFACE) == 0)

             key = "varargs.implement";

         else

             key = "varargs.clash.with";

         return JCDiagnostic.fragment(key, m, m.location(), other, other.location());

     }

     /** Check that this method conforms with overridden method 'other'.

      *  where `origin' is the class where checking started.

      *  Complications:

      *  (1) Do not check overriding of synthetic methods

      *      (reason: they might be final).

      *      todo: check whether this is still necessary.

      *  (2) Admit the case where an interface proxy throws fewer exceptions

      *      than the method it implements. Augment the proxy methods with the

      *      undeclared exceptions in this case.

      *  (3) When generics are enabled, admit the case where an interface proxy

      *      has a result type

      *      extended by the result type of the method it implements.

      *      Change the proxies result type to the smaller type in this case.

      *

      *  @param tree         The tree from which positions

      *                      are extracted for errors.

      *  @param m            The overriding method.

      *  @param other        The overridden method.

      *  @param origin       The class of which the overriding method

      *                      is a member.

      */

     void checkOverride(JCTree tree,

                        MethodSymbol m,

                        MethodSymbol other,

                        ClassSymbol origin) {

         // Don't check overriding of synthetic methods or by bridge methods.

         if ((m.flags() & (SYNTHETIC|BRIDGE)) != 0 || (other.flags() & SYNTHETIC) != 0) {

             return;

         }

         // Error if static method overrides instance method (JLS 8.4.6.2).

         if ((m.flags() & STATIC) != 0 &&

                    (other.flags() & STATIC) == 0) {

             log.error(TreeInfo.diagnosticPositionFor(m, tree), "override.static",

                       cannotOverride(m, other));

             return;

         }

         // Error if instance method overrides static or final

         // method (JLS 8.4.6.1).

         if ((other.flags() & FINAL) != 0 ||

                  (m.flags() & STATIC) == 0 &&

                  (other.flags() & STATIC) != 0) {

             log.error(TreeInfo.diagnosticPositionFor(m, tree), "override.meth",

                       cannotOverride(m, other),

                       TreeInfo.flagNames(other.flags() & (FINAL | STATIC)));

             return;

         }

         if ((m.owner.flags() & ANNOTATION) != 0) {

             // handled in validateAnnotationMethod

             return;

         }

         // Error if overriding method has weaker access (JLS 8.4.6.3).

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

                  protection(m.flags()) > protection(other.flags())) {

             log.error(TreeInfo.diagnosticPositionFor(m, tree), "override.weaker.access",

                       cannotOverride(m, other),

                       protectionString(other.flags()));

             return;

         }

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

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

         // Error if overriding result type is different

         // (or, in the case of generics mode, not a subtype) of

         // overridden result type. We have to rename any type parameters

         // before comparing types.

         List<Type> mtvars = mt.getTypeArguments();

         List<Type> otvars = ot.getTypeArguments();

         Type mtres = mt.getReturnType();

         Type otres = types.subst(ot.getReturnType(), otvars, mtvars);

         overrideWarner.warned = false;

         boolean resultTypesOK =

             types.returnTypeSubstitutable(mt, ot, otres, overrideWarner);

         if (!resultTypesOK) {

             if (!source.allowCovariantReturns() &&

                 m.owner != origin &&

                 m.owner.isSubClass(other.owner, types)) {

                 // allow limited interoperability with covariant returns

             } else {

                 typeError(TreeInfo.diagnosticPositionFor(m, tree),

                           JCDiagnostic.fragment("override.incompatible.ret",

                                          cannotOverride(m, other)),

                           mtres, otres);

                 return;

             }

         } else if (overrideWarner.warned) {

             warnUnchecked(TreeInfo.diagnosticPositionFor(m, tree),

                           "prob.found.req",

                           JCDiagnostic.fragment("override.unchecked.ret",

                                               uncheckedOverrides(m, other)),

                           mtres, otres);

         }

         // Error if overriding method throws an exception not reported

         // by overridden method.

         List<Type> otthrown = types.subst(ot.getThrownTypes(), otvars, mtvars);

         List<Type> unhandled = unHandled(mt.getThrownTypes(), otthrown);

         if (unhandled.nonEmpty()) {

             log.error(TreeInfo.diagnosticPositionFor(m, tree),

                       "override.meth.doesnt.throw",

                       cannotOverride(m, other),

                       unhandled.head);

             return;

         }

         // Optional warning if varargs don't agree

         if ((((m.flags() ^ other.flags()) & Flags.VARARGS) != 0)

             && lint.isEnabled(Lint.LintCategory.OVERRIDES)) {

             log.warning(TreeInfo.diagnosticPositionFor(m, tree),

                         ((m.flags() & Flags.VARARGS) != 0)

                         ? "override.varargs.missing"

                         : "override.varargs.extra",

                         varargsOverrides(m, other));

         }

         // Warn if instance method overrides bridge method (compiler spec ??)

         if ((other.flags() & BRIDGE) != 0) {

             log.warning(TreeInfo.diagnosticPositionFor(m, tree), "override.bridge",

                         uncheckedOverrides(m, other));

         }

         // Warn if a deprecated method overridden by a non-deprecated one.

         if ((other.flags() & DEPRECATED) != 0

             && (m.flags() & DEPRECATED) == 0

             && m.outermostClass() != other.outermostClass()

             && !isDeprecatedOverrideIgnorable(other, origin)) {

             warnDeprecated(TreeInfo.diagnosticPositionFor(m, tree), other);

         }

     }

     // where

         private boolean isDeprecatedOverrideIgnorable(MethodSymbol m, ClassSymbol origin) {

             // If the method, m, is defined in an interface, then ignore the issue if the method

             // is only inherited via a supertype and also implemented in the supertype,

             // because in that case, we will rediscover the issue when examining the method

             // in the supertype.

             // If the method, m, is not defined in an interface, then the only time we need to

             // address the issue is when the method is the supertype implemementation: any other

             // case, we will have dealt with when examining the supertype classes

             ClassSymbol mc = m.enclClass();

             Type st = types.supertype(origin.type);

             if (st.tag != CLASS)

                 return true;

             MethodSymbol stimpl = m.implementation((ClassSymbol)st.tsym, types, false);

             if (mc != null && ((mc.flags() & INTERFACE) != 0)) {

                 List<Type> intfs = types.interfaces(origin.type);

                 return (intfs.contains(mc.type) ? false : (stimpl != null));

             }

             else

                 return (stimpl != m);

         }

     // used to check if there were any unchecked conversions

     Warner overrideWarner = new Warner();

     /** Check that a class does not inherit two concrete methods

      *  with the same signature.

      *  @param pos          Position to be used for error reporting.

      *  @param site         The class type to be checked.

      */

     public void checkCompatibleConcretes(DiagnosticPosition pos, Type site) {

         Type sup = types.supertype(site);

         if (sup.tag != CLASS) return;

         for (Type t1 = sup;

              t1.tsym.type.isParameterized();

              t1 = types.supertype(t1)) {

             for (Scope.Entry e1 = t1.tsym.members().elems;

                  e1 != null;

                  e1 = e1.sibling) {

                 Symbol s1 = e1.sym;

                 if (s1.kind != MTH ||

                     (s1.flags() & (STATIC|SYNTHETIC|BRIDGE)) != 0 ||

                     !s1.isInheritedIn(site.tsym, types) ||

                     ((MethodSymbol)s1).implementation(site.tsym,

                                                       types,

                                                       true) != s1)

                     continue;

                 Type st1 = types.memberType(t1, s1);

                 int s1ArgsLength = st1.getParameterTypes().length();

                 if (st1 == s1.type) continue;

                 for (Type t2 = sup;

                      t2.tag == CLASS;

                      t2 = types.supertype(t2)) {

                     for (Scope.Entry e2 = t2.tsym.members().lookup(s1.name);

                          e2.scope != null;

                          e2 = e2.next()) {

                         Symbol s2 = e2.sym;

                         if (s2 == s1 ||

                             s2.kind != MTH ||

                             (s2.flags() & (STATIC|SYNTHETIC|BRIDGE)) != 0 ||

                             s2.type.getParameterTypes().length() != s1ArgsLength ||

                             !s2.isInheritedIn(site.tsym, types) ||

                             ((MethodSymbol)s2).implementation(site.tsym,

                                                               types,

                                                               true) != s2)

                             continue;

                         Type st2 = types.memberType(t2, s2);

                         if (types.overrideEquivalent(st1, st2))

                             log.error(pos, "concrete.inheritance.conflict",

                                       s1, t1, s2, t2, sup);

                     }

                 }

             }

         }

     }

     /** Check that classes (or interfaces) do not each define an abstract

      *  method with same name and arguments but incompatible return types.

      *  @param pos          Position to be used for error reporting.

      *  @param t1           The first argument type.

      *  @param t2           The second argument type.

      */

     public boolean checkCompatibleAbstracts(DiagnosticPosition pos,

                                             Type t1,

                                             Type t2) {

         return checkCompatibleAbstracts(pos, t1, t2,

                                         types.makeCompoundType(t1, t2));

     }

     public boolean checkCompatibleAbstracts(DiagnosticPosition pos,

                                             Type t1,

                                             Type t2,

                                             Type site) {

         Symbol sym = firstIncompatibility(t1, t2, site);

         if (sym != null) {

             log.error(pos, "types.incompatible.diff.ret",

                       t1, t2, sym.name +

                       "(" + types.memberType(t2, sym).getParameterTypes() + ")");

             return false;

         }

         return true;

     }

     /** Return the first method which is defined with same args

      *  but different return types in two given interfaces, or null if none

      *  exists.

      *  @param t1     The first type.

      *  @param t2     The second type.

      *  @param site   The most derived type.

      *  @returns symbol from t2 that conflicts with one in t1.

      */

     private Symbol firstIncompatibility(Type t1, Type t2, Type site) {

         Map<TypeSymbol,Type> interfaces1 = new HashMap<TypeSymbol,Type>();

         closure(t1, interfaces1);

         Map<TypeSymbol,Type> interfaces2;

         if (t1 == t2)

             interfaces2 = interfaces1;

         else

             closure(t2, interfaces1, interfaces2 = new HashMap<TypeSymbol,Type>());

         for (Type t3 : interfaces1.values()) {

             for (Type t4 : interfaces2.values()) {

                 Symbol s = firstDirectIncompatibility(t3, t4, site);

                 if (s != null) return s;

             }

         }

         return null;

     }

     /** Compute all the supertypes of t, indexed by type symbol. */

     private void closure(Type t, Map<TypeSymbol,Type> typeMap) {

         if (t.tag != CLASS) return;

         if (typeMap.put(t.tsym, t) == null) {

             closure(types.supertype(t), typeMap);

             for (Type i : types.interfaces(t))

                 closure(i, typeMap);

         }

     }

     /** Compute all the supertypes of t, indexed by type symbol (except thise in typesSkip). */

     private void closure(Type t, Map<TypeSymbol,Type> typesSkip, Map<TypeSymbol,Type> typeMap) {

         if (t.tag != CLASS) return;

         if (typesSkip.get(t.tsym) != null) return;

         if (typeMap.put(t.tsym, t) == null) {

             closure(types.supertype(t), typesSkip, typeMap);

             for (Type i : types.interfaces(t))

                 closure(i, typesSkip, typeMap);

         }

     }

     /** Return the first method in t2 that conflicts with a method from t1. */

     private Symbol firstDirectIncompatibility(Type t1, Type t2, Type site) {

         for (Scope.Entry e1 = t1.tsym.members().elems; e1 != null; e1 = e1.sibling) {

             Symbol s1 = e1.sym;

             Type st1 = null;

             if (s1.kind != MTH || !s1.isInheritedIn(site.tsym, types)) continue;

             Symbol impl = ((MethodSymbol)s1).implementation(site.tsym, types, false);

             if (impl != null && (impl.flags() & ABSTRACT) == 0) continue;

             for (Scope.Entry e2 = t2.tsym.members().lookup(s1.name); e2.scope != null; e2 = e2.next()) {

                 Symbol s2 = e2.sym;

                 if (s1 == s2) continue;

                 if (s2.kind != MTH || !s2.isInheritedIn(site.tsym, types)) continue;

                 if (st1 == null) st1 = types.memberType(t1, s1);

                 Type st2 = types.memberType(t2, s2);

                 if (types.overrideEquivalent(st1, st2)) {

                     List<Type> tvars1 = st1.getTypeArguments();

                     List<Type> tvars2 = st2.getTypeArguments();

                     Type rt1 = st1.getReturnType();

                     Type rt2 = types.subst(st2.getReturnType(), tvars2, tvars1);

                     boolean compat =

                         types.isSameType(rt1, rt2) ||

                         rt1.tag >= CLASS && rt2.tag >= CLASS &&

                         (types.covariantReturnType(rt1, rt2, Warner.noWarnings) ||

                          types.covariantReturnType(rt2, rt1, Warner.noWarnings));

                     if (!compat) return s2;

                 }

             }

         }

         return null;

     }

     /** Check that a given method conforms with any method it overrides.

      *  @param tree         The tree from which positions are extracted

      *                      for errors.

      *  @param m            The overriding method.

      */

     void checkOverride(JCTree tree, MethodSymbol m) {

         ClassSymbol origin = (ClassSymbol)m.owner;

         if ((origin.flags() & ENUM) != 0 && names.finalize.equals(m.name))

             if (m.overrides(syms.enumFinalFinalize, origin, types, false)) {

                 log.error(tree.pos(), "enum.no.finalize");

                 return;

             }

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

              t = types.supertype(t)) {

             TypeSymbol c = t.tsym;

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

             while (e.scope != null) {

                 if (m.overrides(e.sym, origin, types, false))

                     checkOverride(tree, m, (MethodSymbol)e.sym, origin);

                 else if (e.sym.isInheritedIn(origin, types) && !m.isConstructor()) {

                     Type er1 = m.erasure(types);

                     Type er2 = e.sym.erasure(types);

                     if (types.isSameType(er1,er2)) {

                             log.error(TreeInfo.diagnosticPositionFor(m, tree),

                                     "name.clash.same.erasure.no.override",

                                     m, m.location(),

                                     e.sym, e.sym.location());

                     }

                 }

                 e = e.next();

             }

         }

     }

     /** Check that all abstract members of given class have definitions.

      *  @param pos          Position to be used for error reporting.

      *  @param c            The class.

      */

     void checkAllDefined(DiagnosticPosition pos, ClassSymbol c) {

         try {

             MethodSymbol undef = firstUndef(c, c);

             if (undef != null) {

                 if ((c.flags() & ENUM) != 0 &&

                     types.supertype(c.type).tsym == syms.enumSym &&

                     (c.flags() & FINAL) == 0) {

                     // add the ABSTRACT flag to an enum

                     c.flags_field |= ABSTRACT;

                 } else {

                     MethodSymbol undef1 =

                         new MethodSymbol(undef.flags(), undef.name,

                                          types.memberType(c.type, undef), undef.owner);

                     log.error(pos, "does.not.override.abstract",

                               c, undef1, undef1.location());

                 }

             }

         } catch (CompletionFailure ex) {

             completionError(pos, ex);

         }

     }

 //where

         /** Return first abstract member of class `c' that is not defined

          *  in `impl', null if there is none.

          */

         private MethodSymbol firstUndef(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 (Scope.Entry e = s.elems;

                      undef == null && e != null;

                      e = e.sibling) {

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

                         (e.sym.flags() & (ABSTRACT|IPROXY)) == ABSTRACT) {

                         MethodSymbol absmeth = (MethodSymbol)e.sym;

                         MethodSymbol implmeth = absmeth.implementation(impl, types, true);

                         if (implmeth == null || implmeth == absmeth)

                             undef = absmeth;

                     }

                 }

                 if (undef == null) {

                     Type st = types.supertype(c.type);

                     if (st.tag == CLASS)

                         undef = firstUndef(impl, (ClassSymbol)st.tsym);

                 }

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

                      undef == null && l.nonEmpty();

                      l = l.tail) {

                     undef = firstUndef(impl, (ClassSymbol)l.head.tsym);

                 }

             }

             return undef;

         }

     /** Check for cyclic references. Issue an error if the

      *  symbol of the type referred to has a LOCKED flag set.

      *

      *  @param pos      Position to be used for error reporting.

      *  @param t        The type referred to.

      */

     void checkNonCyclic(DiagnosticPosition pos, Type t) {

         checkNonCyclicInternal(pos, t);

     }

     void checkNonCyclic(DiagnosticPosition pos, TypeVar t) {

         checkNonCyclic1(pos, t, new HashSet<TypeVar>());

     }

     private void checkNonCyclic1(DiagnosticPosition pos, Type t, Set<TypeVar> seen) {

         final TypeVar tv;

         if  (t.tag == TYPEVAR && (t.tsym.flags() & UNATTRIBUTED) != 0)

             return;

         if (seen.contains(t)) {

             tv = (TypeVar)t;

             tv.bound = new ErrorType();

             log.error(pos, "cyclic.inheritance", t);

         } else if (t.tag == TYPEVAR) {

             tv = (TypeVar)t;

             seen.add(tv);

             for (Type b : types.getBounds(tv))

                 checkNonCyclic1(pos, b, seen);

         }

     }

     /** Check for cyclic references. Issue an error if the

      *  symbol of the type referred to has a LOCKED flag set.

      *

      *  @param pos      Position to be used for error reporting.

      *  @param t        The type referred to.

      *  @returns        True if the check completed on all attributed classes

      */

     private boolean checkNonCyclicInternal(DiagnosticPosition pos, Type t) {

         boolean complete = true; // was the check complete?

         //- System.err.println("checkNonCyclicInternal("+t+");");//DEBUG

         Symbol c = t.tsym;

         if ((c.flags_field & ACYCLIC) != 0) return true;

         if ((c.flags_field & LOCKED) != 0) {

             noteCyclic(pos, (ClassSymbol)c);

         } else if (!c.type.isErroneous()) {

             try {

                 c.flags_field |= LOCKED;

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

                     ClassType clazz = (ClassType)c.type;

                     if (clazz.interfaces_field != null)

                         for (List<Type> l=clazz.interfaces_field; l.nonEmpty(); l=l.tail)

                             complete &= checkNonCyclicInternal(pos, l.head);

                     if (clazz.supertype_field != null) {

                         Type st = clazz.supertype_field;

                         if (st != null && st.tag == CLASS)

                             complete &= checkNonCyclicInternal(pos, st);

                     }

                     if (c.owner.kind == TYP)

                         complete &= checkNonCyclicInternal(pos, c.owner.type);

                 }

             } finally {

                 c.flags_field &= ~LOCKED;

             }

         }

         if (complete)

             complete = ((c.flags_field & UNATTRIBUTED) == 0) && c.completer == null;

         if (complete) c.flags_field |= ACYCLIC;

         return complete;

     }

     /** Note that we found an inheritance cycle. */

     private void noteCyclic(DiagnosticPosition pos, ClassSymbol c) {

         log.error(pos, "cyclic.inheritance", c);

         for (List<Type> l=types.interfaces(c.type); l.nonEmpty(); l=l.tail)

             l.head = new ErrorType((ClassSymbol)l.head.tsym);

         Type st = types.supertype(c.type);

         if (st.tag == CLASS)

             ((ClassType)c.type).supertype_field = new ErrorType((ClassSymbol)st.tsym);

         c.type = new ErrorType(c);

         c.flags_field |= ACYCLIC;

     }

     /** Check that all methods which implement some

      *  method conform to the method they implement.

      *  @param tree         The class definition whose members are checked.

      */

     void checkImplementations(JCClassDecl tree) {

         checkImplementations(tree, tree.sym);

     }

 //where

         /** Check that all methods which implement some

          *  method in `ic' conform to the method they implement.

          */

         void checkImplementations(JCClassDecl tree, ClassSymbol ic) {

             ClassSymbol origin = tree.sym;

             for (List<Type> l = types.closure(ic.type); l.nonEmpty(); l = l.tail) {

                 ClassSymbol lc = (ClassSymbol)l.head.tsym;

                 if ((allowGenerics || origin != lc) && (lc.flags() & ABSTRACT) != 0) {

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

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

                             (e.sym.flags() & (STATIC|ABSTRACT)) == ABSTRACT) {

                             MethodSymbol absmeth = (MethodSymbol)e.sym;

                             MethodSymbol implmeth = absmeth.implementation(origin, types, false);

                             if (implmeth != null && implmeth != absmeth &&

                                 (implmeth.owner.flags() & INTERFACE) ==

                                 (origin.flags() & INTERFACE)) {

                                 // don't check if implmeth is in a class, yet

                                 // origin is an interface. This case arises only

                                 // if implmeth is declared in Object. The reason is

                                 // that interfaces really don't inherit from

                                 // Object it's just that the compiler represents

                                 // things that way.

                                 checkOverride(tree, implmeth, absmeth, origin);

                             }

                         }

                     }

                 }

             }

         }

     /** Check that all abstract methods implemented by a class are

      *  mutually compatible.

      *  @param pos          Position to be used for error reporting.

      *  @param c            The class whose interfaces are checked.

      */

     void checkCompatibleSupertypes(DiagnosticPosition pos, Type c) {

         List<Type> supertypes = types.interfaces(c);

         Type supertype = types.supertype(c);

         if (supertype.tag == CLASS &&

             (supertype.tsym.flags() & ABSTRACT) != 0)

             supertypes = supertypes.prepend(supertype);

         for (List<Type> l = supertypes; l.nonEmpty(); l = l.tail) {

             if (allowGenerics && !l.head.getTypeArguments().isEmpty() &&

                 !checkCompatibleAbstracts(pos, l.head, l.head, c))

                 return;

             for (List<Type> m = supertypes; m != l; m = m.tail)

                 if (!checkCompatibleAbstracts(pos, l.head, m.head, c))

                     return;

         }

         checkCompatibleConcretes(pos, c);

     }

     /** Check that class c does not implement directly or indirectly

      *  the same parameterized interface with two different argument lists.

      *  @param pos          Position to be used for error reporting.

      *  @param type         The type whose interfaces are checked.

      */

     void checkClassBounds(DiagnosticPosition pos, Type type) {

         checkClassBounds(pos, new HashMap<TypeSymbol,Type>(), type);

     }

 //where

         /** Enter all interfaces of type `type' into the hash table `seensofar'

          *  with their class symbol as key and their type as value. Make

          *  sure no class is entered with two different types.

          */

         void checkClassBounds(DiagnosticPosition pos,

                               Map<TypeSymbol,Type> seensofar,

                               Type type) {

             if (type.isErroneous()) return;

             for (List<Type> l = types.interfaces(type); l.nonEmpty(); l = l.tail) {

                 Type it = l.head;

                 Type oldit = seensofar.put(it.tsym, it);

                 if (oldit != null) {

                     List<Type> oldparams = oldit.allparams();

                     List<Type> newparams = it.allparams();

                     if (!types.containsTypeEquivalent(oldparams, newparams))

                         log.error(pos, "cant.inherit.diff.arg",

                                   it.tsym, Type.toString(oldparams),

                                   Type.toString(newparams));

                 }

                 checkClassBounds(pos, seensofar, it);

             }

             Type st = types.supertype(type);

             if (st != null) checkClassBounds(pos, seensofar, st);

         }

     /** Enter interface into into set.

      *  If it existed already, issue a "repeated interface" error.

      */

     void checkNotRepeated(DiagnosticPosition pos, Type it, Set<Type> its) {

         if (its.contains(it))

             log.error(pos, "repeated.interface");

         else {

             its.add(it);

         }

     }

 /* *************************************************************************

  * Check annotations

  **************************************************************************/

     /** Annotation types are restricted to primitives, String, an

      *  enum, an annotation, Class, Class<?>, Class<? extends

      *  Anything>, arrays of the preceding.

      */

     void validateAnnotationType(JCTree restype) {

         // restype may be null if an error occurred, so don't bother validating it

         if (restype != null) {

             validateAnnotationType(restype.pos(), restype.type);

         }

     }

     void validateAnnotationType(DiagnosticPosition pos, Type type) {

         if (type.isPrimitive()) return;

         if (types.isSameType(type, syms.stringType)) return;

         if ((type.tsym.flags() & Flags.ENUM) != 0) return;

         if ((type.tsym.flags() & Flags.ANNOTATION) != 0) return;

         if (types.lowerBound(type).tsym == syms.classType.tsym) return;

         if (types.isArray(type) && !types.isArray(types.elemtype(type))) {

             validateAnnotationType(pos, types.elemtype(type));

             return;

         }

         log.error(pos, "invalid.annotation.member.type");

     }

     /**

      * "It is also a compile-time error if any method declared in an

      * annotation type has a signature that is override-equivalent to

      * that of any public or protected method declared in class Object

      * or in the interface annotation.Annotation."

      *

      * @jls3 9.6 Annotation Types

      */

     void validateAnnotationMethod(DiagnosticPosition pos, MethodSymbol m) {

         for (Type sup = syms.annotationType; sup.tag == CLASS; sup = types.supertype(sup)) {

             Scope s = sup.tsym.members();

             for (Scope.Entry e = s.lookup(m.name); e.scope != null; e = e.next()) {

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

                     (e.sym.flags() & (PUBLIC | PROTECTED)) != 0 &&

                     types.overrideEquivalent(m.type, e.sym.type))

                     log.error(pos, "intf.annotation.member.clash", e.sym, sup);

             }

         }

     }

     /** Check the annotations of a symbol.

      */

     public void validateAnnotations(List<JCAnnotation> annotations, Symbol s) {

         if (skipAnnotations) return;

         for (JCAnnotation a : annotations)

             validateAnnotation(a, s);

     }

     /** Check an annotation of a symbol.

      */

     public void validateAnnotation(JCAnnotation a, Symbol s) {

         validateAnnotation(a);

         if (!annotationApplicable(a, s))

             log.error(a.pos(), "annotation.type.not.applicable");

         if (a.annotationType.type.tsym == syms.overrideType.tsym) {

             if (!isOverrider(s))

                 log.error(a.pos(), "method.does.not.override.superclass");

         }

     }

     /** Is s a method symbol that overrides a method in a superclass? */

     boolean isOverrider(Symbol s) {

         if (s.kind != MTH || s.isStatic())

             return false;

         MethodSymbol m = (MethodSymbol)s;

         TypeSymbol owner = (TypeSymbol)m.owner;

         for (Type sup : types.closure(owner.type)) {

             if (sup == owner.type)

                 continue; // skip "this"

             Scope scope = sup.tsym.members();

             for (Scope.Entry e = scope.lookup(m.name); e.scope != null; e = e.next()) {

                 if (!e.sym.isStatic() && m.overrides(e.sym, owner, types, true))

                     return true;

             }

         }

         return false;

     }

     /** Is the annotation applicable to the symbol? */

     boolean annotationApplicable(JCAnnotation a, Symbol s) {

         Attribute.Compound atTarget =

             a.annotationType.type.tsym.attribute(syms.annotationTargetType.tsym);

         if (atTarget == null) return true;

         Attribute atValue = atTarget.member(names.value);

         if (!(atValue instanceof Attribute.Array)) return true; // error recovery

         Attribute.Array arr = (Attribute.Array) atValue;

         for (Attribute app : arr.values) {

             if (!(app instanceof Attribute.Enum)) return true; // recovery

             Attribute.Enum e = (Attribute.Enum) app;

             if (e.value.name == names.TYPE)

                 { if (s.kind == TYP) return true; }

             else if (e.value.name == names.FIELD)

                 { if (s.kind == VAR && s.owner.kind != MTH) return true; }

             else if (e.value.name == names.METHOD)

                 { if (s.kind == MTH && !s.isConstructor()) return true; }

             else if (e.value.name == names.PARAMETER)

                 { if (s.kind == VAR &&

                       s.owner.kind == MTH &&

                       (s.flags() & PARAMETER) != 0)

                     return true;

                 }

             else if (e.value.name == names.CONSTRUCTOR)

                 { if (s.kind == MTH && s.isConstructor()) return true; }

             else if (e.value.name == names.LOCAL_VARIABLE)

                 { if (s.kind == VAR && s.owner.kind == MTH &&

                       (s.flags() & PARAMETER) == 0)

                     return true;

                 }

             else if (e.value.name == names.ANNOTATION_TYPE)

                 { if (s.kind == TYP && (s.flags() & ANNOTATION) != 0)

                     return true;

                 }

             else if (e.value.name == names.PACKAGE)

                 { if (s.kind == PCK) return true; }

             else

                 return true; // recovery

         }

         return false;

     }

     /** Check an annotation value.

      */

     public void validateAnnotation(JCAnnotation a) {

         if (a.type.isErroneous()) return;

         // collect an inventory of the members

         Set<MethodSymbol> members = new HashSet<MethodSymbol>();

         for (Scope.Entry e = a.annotationType.type.tsym.members().elems;

              e != null;

              e = e.sibling)

             if (e.sym.kind == MTH)

                 members.add((MethodSymbol) e.sym);

         // count them off as they're annotated

         for (JCTree arg : a.args) {

             if (arg.getTag() != JCTree.ASSIGN) continue; // recovery

             JCAssign assign = (JCAssign) arg;

             Symbol m = TreeInfo.symbol(assign.lhs);

             if (m == null || m.type.isErroneous()) continue;

             if (!members.remove(m))

                 log.error(arg.pos(), "duplicate.annotation.member.value",

                           m.name, a.type);

             if (assign.rhs.getTag() == ANNOTATION)

                 validateAnnotation((JCAnnotation)assign.rhs);

         }

         // all the remaining ones better have default values

         for (MethodSymbol m : members)

             if (m.defaultValue == null && !m.type.isErroneous())

                 log.error(a.pos(), "annotation.missing.default.value",

                           a.type, m.name);

         // special case: java.lang.annotation.Target must not have

         // repeated values in its value member

         if (a.annotationType.type.tsym != syms.annotationTargetType.tsym ||

             a.args.tail == null)

             return;

         if (a.args.head.getTag() != JCTree.ASSIGN) return; // error recovery

         JCAssign assign = (JCAssign) a.args.head;

         Symbol m = TreeInfo.symbol(assign.lhs);

         if (m.name != names.value) return;

         JCTree rhs = assign.rhs;

         if (rhs.getTag() != JCTree.NEWARRAY) return;

         JCNewArray na = (JCNewArray) rhs;

         Set<Symbol> targets = new HashSet<Symbol>();

         for (JCTree elem : na.elems) {

             if (!targets.add(TreeInfo.symbol(elem))) {

                 log.error(elem.pos(), "repeated.annotation.target");

             }

         }

     }

     void checkDeprecatedAnnotation(DiagnosticPosition pos, Symbol s) {

         if (allowAnnotations &&

             lint.isEnabled(Lint.LintCategory.DEP_ANN) &&

             (s.flags() & DEPRECATED) != 0 &&

             !syms.deprecatedType.isErroneous() &&

             s.attribute(syms.deprecatedType.tsym) == null) {

             log.warning(pos, "missing.deprecated.annotation");

         }

     }

 /* *************************************************************************

  * Check for recursive annotation elements.

  **************************************************************************/

     /** Check for cycles in the graph of annotation elements.

      */

     void checkNonCyclicElements(JCClassDecl tree) {

         if ((tree.sym.flags_field & ANNOTATION) == 0) return;

         assert (tree.sym.flags_field & LOCKED) == 0;

         try {

             tree.sym.flags_field |= LOCKED;

             for (JCTree def : tree.defs) {

                 if (def.getTag() != JCTree.METHODDEF) continue;

                 JCMethodDecl meth = (JCMethodDecl)def;

                 checkAnnotationResType(meth.pos(), meth.restype.type);

             }

         } finally {

             tree.sym.flags_field &= ~LOCKED;

             tree.sym.flags_field |= ACYCLIC_ANN;

         }

     }

     void checkNonCyclicElementsInternal(DiagnosticPosition pos, TypeSymbol tsym) {

         if ((tsym.flags_field & ACYCLIC_ANN) != 0)

             return;

         if ((tsym.flags_field & LOCKED) != 0) {

             log.error(pos, "cyclic.annotation.element");

             return;

         }

         try {

             tsym.flags_field |= LOCKED;

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

                 Symbol s = e.sym;

                 if (s.kind != Kinds.MTH)

                     continue;

                 checkAnnotationResType(pos, ((MethodSymbol)s).type.getReturnType());

             }

         } finally {

             tsym.flags_field &= ~LOCKED;

             tsym.flags_field |= ACYCLIC_ANN;

         }

     }

     void checkAnnotationResType(DiagnosticPosition pos, Type type) {

         switch (type.tag) {

         case TypeTags.CLASS:

             if ((type.tsym.flags() & ANNOTATION) != 0)

                 checkNonCyclicElementsInternal(pos, type.tsym);

             break;

         case TypeTags.ARRAY:

             checkAnnotationResType(pos, types.elemtype(type));

             break;

         default:

             break; // int etc

         }

     }

 /* *************************************************************************

  * Check for cycles in the constructor call graph.

  **************************************************************************/

     /** Check for cycles in the graph of constructors calling other

      *  constructors.

      */

     void checkCyclicConstructors(JCClassDecl tree) {

         Map<Symbol,Symbol> callMap = new HashMap<Symbol, Symbol>();

         // enter each constructor this-call into the map

         for (List<JCTree> l = tree.defs; l.nonEmpty(); l = l.tail) {

             JCMethodInvocation app = TreeInfo.firstConstructorCall(l.head);

             if (app == null) continue;

             JCMethodDecl meth = (JCMethodDecl) l.head;

             if (TreeInfo.name(app.meth) == names._this) {

                 callMap.put(meth.sym, TreeInfo.symbol(app.meth));

             } else {

                 meth.sym.flags_field |= ACYCLIC;

             }

         }

         // Check for cycles in the map

         Symbol[] ctors = new Symbol[0];

         ctors = callMap.keySet().toArray(ctors);

         for (Symbol caller : ctors) {

             checkCyclicConstructor(tree, caller, callMap);

         }

     }

     /** Look in the map to see if the given constructor is part of a

      *  call cycle.

      */

     private void checkCyclicConstructor(JCClassDecl tree, Symbol ctor,

                                         Map<Symbol,Symbol> callMap) {

         if (ctor != null && (ctor.flags_field & ACYCLIC) == 0) {

             if ((ctor.flags_field & LOCKED) != 0) {

                 log.error(TreeInfo.diagnosticPositionFor(ctor, tree),

                           "recursive.ctor.invocation");

             } else {

                 ctor.flags_field |= LOCKED;

                 checkCyclicConstructor(tree, callMap.remove(ctor), callMap);

                 ctor.flags_field &= ~LOCKED;

             }

             ctor.flags_field |= ACYCLIC;

         }

     }

 /* *************************************************************************

  * Miscellaneous

  **************************************************************************/

     /**

      * Return the opcode of the operator but emit an error if it is an

      * error.

      * @param pos        position for error reporting.

      * @param operator   an operator

      * @param tag        a tree tag

      * @param left       type of left hand side

      * @param right      type of right hand side

      */

     int checkOperator(DiagnosticPosition pos,

                        OperatorSymbol operator,

                        int tag,

                        Type left,

                        Type right) {

         if (operator.opcode == ByteCodes.error) {

             log.error(pos,

                       "operator.cant.be.applied",

                       treeinfo.operatorName(tag),

                       left + "," + right);

         }

         return operator.opcode;

     }

     /**

      *  Check for division by integer constant zero

      *  @param pos           Position for error reporting.

      *  @param operator      The operator for the expression

      *  @param operand       The right hand operand for the expression

      */

     void checkDivZero(DiagnosticPosition pos, Symbol operator, Type operand) {

         if (operand.constValue() != null

             && lint.isEnabled(Lint.LintCategory.DIVZERO)

             && operand.tag <= LONG

             && ((Number) (operand.constValue())).longValue() == 0) {

             int opc = ((OperatorSymbol)operator).opcode;

             if (opc == ByteCodes.idiv || opc == ByteCodes.imod

                 || opc == ByteCodes.ldiv || opc == ByteCodes.lmod) {

                 log.warning(pos, "div.zero");

             }

         }

     }

     /**

      * Check for empty statements after if

      */

     void checkEmptyIf(JCIf tree) {

         if (tree.thenpart.getTag() == JCTree.SKIP && tree.elsepart == null && lint.isEnabled(Lint.LintCategory.EMPTY))

             log.warning(tree.thenpart.pos(), "empty.if");

     }

     /** Check that symbol is unique in given scope.

      *  @param pos           Position for error reporting.

      *  @param sym           The symbol.

      *  @param s             The scope.

      */

     boolean checkUnique(DiagnosticPosition pos, Symbol sym, Scope s) {

         if (sym.type.isErroneous())

             return true;

         if (sym.owner.name == names.any) return false;

         for (Scope.Entry e = s.lookup(sym.name); e.scope == s; e = e.next()) {

             if (sym != e.sym &&

                 sym.kind == e.sym.kind &&

                 sym.name != names.error &&

                 (sym.kind != MTH || types.overrideEquivalent(sym.type, e.sym.type))) {

                 if ((sym.flags() & VARARGS) != (e.sym.flags() & VARARGS))

                     varargsDuplicateError(pos, sym, e.sym);

                 else

                     duplicateError(pos, e.sym);

                 return false;

             }

         }

         return true;

     }

     /** Check that single-type import is not already imported or top-level defined,

      *  but make an exception for two single-type imports which denote the same type.

      *  @param pos           Position for error reporting.

      *  @param sym           The symbol.

      *  @param s             The scope

      */

     boolean checkUniqueImport(DiagnosticPosition pos, Symbol sym, Scope s) {

         return checkUniqueImport(pos, sym, s, false);

     }

     /** Check that static single-type import is not already imported or top-level defined,

      *  but make an exception for two single-type imports which denote the same type.

      *  @param pos           Position for error reporting.

      *  @param sym           The symbol.

      *  @param s             The scope

      *  @param staticImport  Whether or not this was a static import

      */

     boolean checkUniqueStaticImport(DiagnosticPosition pos, Symbol sym, Scope s) {

         return checkUniqueImport(pos, sym, s, true);

     }

     /** Check that single-type import is not already imported or top-level defined,

      *  but make an exception for two single-type imports which denote the same type.

      *  @param pos           Position for error reporting.

      *  @param sym           The symbol.

      *  @param s             The scope.

      *  @param staticImport  Whether or not this was a static import

      */

     private boolean checkUniqueImport(DiagnosticPosition pos, Symbol sym, Scope s, boolean staticImport) {

         for (Scope.Entry e = s.lookup(sym.name); e.scope != null; e = e.next()) {

             // is encountered class entered via a class declaration?

             boolean isClassDecl = e.scope == s;

             if ((isClassDecl || sym != e.sym) &&

                 sym.kind == e.sym.kind &&

                 sym.name != names.error) {

                 if (!e.sym.type.isErroneous()) {

                     String what = e.sym.toString();

                     if (!isClassDecl) {

                         if (staticImport)

                             log.error(pos, "already.defined.static.single.import", what);

                         else

                             log.error(pos, "already.defined.single.import", what);

                     }

                     else if (sym != e.sym)

                         log.error(pos, "already.defined.this.unit", what);

                 }

                 return false;

             }

         }

         return true;

     }

     /** Check that a qualified name is in canonical form (for import decls).

      */

     public void checkCanonical(JCTree tree) {

         if (!isCanonical(tree))

             log.error(tree.pos(), "import.requires.canonical",

                       TreeInfo.symbol(tree));

     }

         // where

         private boolean isCanonical(JCTree tree) {

             while (tree.getTag() == JCTree.SELECT) {

                 JCFieldAccess s = (JCFieldAccess) tree;

                 if (s.sym.owner != TreeInfo.symbol(s.selected))

                     return false;

                 tree = s.selected;

             }

             return true;

         }

     private class ConversionWarner extends Warner {

         final String key;

         final Type found;

         final Type expected;

         public ConversionWarner(DiagnosticPosition pos, String key, Type found, Type expected) {

             super(pos);

             this.key = key;

             this.found = found;

             this.expected = expected;

         }

         public void warnUnchecked() {

             boolean warned = this.warned;

             super.warnUnchecked();

             if (warned) return; // suppress redundant diagnostics

             Object problem = JCDiagnostic.fragment(key);

             Check.this.warnUnchecked(pos(), "prob.found.req", problem, found, expected);

         }

     }

     public Warner castWarner(DiagnosticPosition pos, Type found, Type expected) {

         return new ConversionWarner(pos, "unchecked.cast.to.type", found, expected);

     }

     public Warner convertWarner(DiagnosticPosition pos, Type found, Type expected) {

         return new ConversionWarner(pos, "unchecked.assign", found, expected);

     }

 }