/*
 * Copyright (c) 1999, 2020, 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.comp;

import java.util.*;
import java.util.function.Supplier;

import javax.lang.model.element.ElementKind;
import javax.tools.JavaFileManager;

import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Attribute.Compound;
import com.sun.tools.javac.code.Directive.ExportsDirective;
import com.sun.tools.javac.code.Directive.RequiresDirective;
import com.sun.tools.javac.code.Source.Feature;
import com.sun.tools.javac.comp.Annotate.AnnotationTypeMetadata;
import com.sun.tools.javac.jvm.*;
import com.sun.tools.javac.resources.CompilerProperties.Errors;
import com.sun.tools.javac.resources.CompilerProperties.Fragments;
import com.sun.tools.javac.resources.CompilerProperties.Warnings;
import com.sun.tools.javac.tree.*;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticFlag;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
import com.sun.tools.javac.util.JCDiagnostic.Error;
import com.sun.tools.javac.util.JCDiagnostic.Fragment;
import com.sun.tools.javac.util.JCDiagnostic.Warning;
import com.sun.tools.javac.util.List;

import com.sun.tools.javac.code.Lint;
import com.sun.tools.javac.code.Lint.LintCategory;
import com.sun.tools.javac.code.Scope.WriteableScope;
import com.sun.tools.javac.code.Type.*;
import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.comp.DeferredAttr.DeferredAttrContext;
import com.sun.tools.javac.tree.JCTree.*;

import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Flags.ANNOTATION;
import static com.sun.tools.javac.code.Flags.SYNCHRONIZED;
import static com.sun.tools.javac.code.Kinds.*;
import static com.sun.tools.javac.code.Kinds.Kind.*;
import static com.sun.tools.javac.code.Scope.LookupKind.NON_RECURSIVE;
import static com.sun.tools.javac.code.TypeTag.*;
import static com.sun.tools.javac.code.TypeTag.WILDCARD;

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

Type checking helper class for the attribution phase.
 
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.
/** Type checking helper class for the attribution phase.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Check {
    protected static final Context.Key<Check> checkKey = new Context.Key<>();

    private final Names names;
    private final Log log;
    private final Resolve rs;
    private final Symtab syms;
    private final Enter enter;
    private final DeferredAttr deferredAttr;
    private final Infer infer;
    private final Types types;
    private final TypeAnnotations typeAnnotations;
    private final JCDiagnostic.Factory diags;
    private final JavaFileManager fileManager;
    private final Source source;
    private final Target target;
    private final Profile profile;
    private final Preview preview;
    private final boolean warnOnAnyAccessToMembers;

    // 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;

    // The method being analyzed in Attr - it is set/reset as needed by
    // Attr as it visits new method declarations.
    private MethodSymbol method;

    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 = Names.instance(context);
        dfltTargetMeta = new Name[] { names.PACKAGE, names.TYPE,
            names.FIELD, names.RECORD_COMPONENT, names.METHOD, names.CONSTRUCTOR,
            names.ANNOTATION_TYPE, names.LOCAL_VARIABLE, names.PARAMETER};
        log = Log.instance(context);
        rs = Resolve.instance(context);
        syms = Symtab.instance(context);
        enter = Enter.instance(context);
        deferredAttr = DeferredAttr.instance(context);
        infer = Infer.instance(context);
        types = Types.instance(context);
        typeAnnotations = TypeAnnotations.instance(context);
        diags = JCDiagnostic.Factory.instance(context);
        Options options = Options.instance(context);
        lint = Lint.instance(context);
        fileManager = context.get(JavaFileManager.class);

        source = Source.instance(context);
        target = Target.instance(context);
        warnOnAnyAccessToMembers = options.isSet("warnOnAccessToMembers");

        Target target = Target.instance(context);
        syntheticNameChar = target.syntheticNameChar();

        profile = Profile.instance(context);
        preview = Preview.instance(context);

        boolean verboseDeprecated = lint.isEnabled(LintCategory.DEPRECATION);
        boolean verboseRemoval = lint.isEnabled(LintCategory.REMOVAL);
        boolean verboseUnchecked = lint.isEnabled(LintCategory.UNCHECKED);
        boolean enforceMandatoryWarnings = true;

        deprecationHandler = new MandatoryWarningHandler(log, verboseDeprecated,
                enforceMandatoryWarnings, "deprecated", LintCategory.DEPRECATION);
        removalHandler = new MandatoryWarningHandler(log, verboseRemoval,
                enforceMandatoryWarnings, "removal", LintCategory.REMOVAL);
        uncheckedHandler = new MandatoryWarningHandler(log, verboseUnchecked,
                enforceMandatoryWarnings, "unchecked", LintCategory.UNCHECKED);
        sunApiHandler = new MandatoryWarningHandler(log, false,
                enforceMandatoryWarnings, "sunapi", null);

        deferredLintHandler = DeferredLintHandler.instance(context);
    }

    
Character for synthetic names
/** Character for synthetic names
     */
    char syntheticNameChar;

    
A table mapping flat names of all compiled classes for each module in this run
 to their symbols; maintained from outside.
/** A table mapping flat names of all compiled classes for each module in this run
     *  to their symbols; maintained from outside.
     */
    private Map<Pair<ModuleSymbol, Name>,ClassSymbol> compiled = new HashMap<>();

    
A handler for messages about deprecated usage.
/** A handler for messages about deprecated usage.
     */
    private MandatoryWarningHandler deprecationHandler;

    
A handler for messages about deprecated-for-removal usage.
/** A handler for messages about deprecated-for-removal usage.
     */
    private MandatoryWarningHandler removalHandler;

    
A handler for messages about unchecked or unsafe usage.
/** A handler for messages about unchecked or unsafe usage.
     */
    private MandatoryWarningHandler uncheckedHandler;

    
A handler for messages about using proprietary API.
/** A handler for messages about using proprietary API.
     */
    private MandatoryWarningHandler sunApiHandler;

    
A handler for deferred lint warnings.
/** A handler for deferred lint warnings.
     */
    private DeferredLintHandler deferredLintHandler;

/* *************************************************************************
 * Errors and Warnings
 **************************************************************************/

    Lint setLint(Lint newLint) {
        Lint prev = lint;
        lint = newLint;
        return prev;
    }

    MethodSymbol setMethod(MethodSymbol newMethod) {
        MethodSymbol prev = method;
        method = newMethod;
        return prev;
    }

    
Warn about deprecated symbol.
 @param pos        Position to be used for error reporting.
 @param sym        The deprecated symbol.
/** 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 (sym.isDeprecatedForRemoval()) {
            if (!lint.isSuppressed(LintCategory.REMOVAL)) {
                if (sym.kind == MDL) {
                    removalHandler.report(pos, Warnings.HasBeenDeprecatedForRemovalModule(sym));
                } else {
                    removalHandler.report(pos, Warnings.HasBeenDeprecatedForRemoval(sym, sym.location()));
                }
            }
        } else if (!lint.isSuppressed(LintCategory.DEPRECATION)) {
            if (sym.kind == MDL) {
                deprecationHandler.report(pos, Warnings.HasBeenDeprecatedModule(sym));
            } else {
                deprecationHandler.report(pos, Warnings.HasBeenDeprecated(sym, sym.location()));
            }
        }
    }

    
Warn about deprecated symbol.
 @param pos        Position to be used for error reporting.
 @param sym        The deprecated symbol.
/** Warn about deprecated symbol.
     *  @param pos        Position to be used for error reporting.
     *  @param sym        The deprecated symbol.
     */
    void warnPreview(DiagnosticPosition pos, Symbol sym) {
        warnPreview(pos, Warnings.IsPreview(sym));
    }

    
Log a preview warning.
 @param pos        Position to be used for error reporting.
 @param msg        A Warning describing the problem.
/** Log a preview warning.
     *  @param pos        Position to be used for error reporting.
     *  @param msg        A Warning describing the problem.
     */
    public void warnPreview(DiagnosticPosition pos, Warning warnKey) {
        if (!lint.isSuppressed(LintCategory.PREVIEW))
            preview.reportPreviewWarning(pos, warnKey);
    }

    
Warn about unchecked operation.
 @param pos        Position to be used for error reporting.
 @param msg        A string describing the problem.
/** 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, Warning warnKey) {
        if (!lint.isSuppressed(LintCategory.UNCHECKED))
            uncheckedHandler.report(pos, warnKey);
    }

    
Warn about unsafe vararg method decl.
 @param pos        Position to be used for error reporting.
/** Warn about unsafe vararg method decl.
     *  @param pos        Position to be used for error reporting.
     */
    void warnUnsafeVararg(DiagnosticPosition pos, Warning warnKey) {
        if (lint.isEnabled(LintCategory.VARARGS))
            log.warning(LintCategory.VARARGS, pos, warnKey);
    }

    public void warnStatic(DiagnosticPosition pos, Warning warnKey) {
        if (lint.isEnabled(LintCategory.STATIC))
            log.warning(LintCategory.STATIC, pos, warnKey);
    }

    
Warn about division by integer constant zero.
 @param pos        Position to be used for error reporting.
/** Warn about division by integer constant zero.
     *  @param pos        Position to be used for error reporting.
     */
    void warnDivZero(DiagnosticPosition pos) {
        if (lint.isEnabled(LintCategory.DIVZERO))
            log.warning(LintCategory.DIVZERO, pos, Warnings.DivZero);
    }

    
Report any deferred diagnostics.
/**
     * Report any deferred diagnostics.
     */
    public void reportDeferredDiagnostics() {
        deprecationHandler.reportDeferredDiagnostic();
        removalHandler.reportDeferredDiagnostic();
        uncheckedHandler.reportDeferredDiagnostic();
        sunApiHandler.reportDeferredDiagnostic();
    }


    
Report a failure to complete a class.
 @param pos        Position to be used for error reporting.
 @param ex         The failure to report.
/** 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(JCDiagnostic.DiagnosticFlag.NON_DEFERRABLE, pos, Errors.CantAccess(ex.sym, ex.getDetailValue()));
        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.
/** 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, JCDiagnostic required, Object found) {
        // this error used to be raised by the parser,
        // but has been delayed to this point:
        if (found instanceof Type && ((Type)found).hasTag(VOID)) {
            log.error(pos, Errors.IllegalStartOfType);
            return syms.errType;
        }
        log.error(pos, Errors.TypeFoundReq(found, required));
        return types.createErrorType(found instanceof Type ? (Type)found : 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.
/** 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, Errors.CantRefBeforeCtorCalled(sym));
    }

    
Report duplicate declaration error.
/** Report duplicate declaration error.
     */
    void duplicateError(DiagnosticPosition pos, Symbol sym) {
        if (!sym.type.isErroneous()) {
            Symbol location = sym.location();
            if (location.kind == MTH &&
                    ((MethodSymbol)location).isStaticOrInstanceInit()) {
                log.error(pos,
                          Errors.AlreadyDefinedInClinit(kindName(sym),
                                                        sym,
                                                        kindName(sym.location()),
                                                        kindName(sym.location().enclClass()),
                                                        sym.location().enclClass()));
            } else {
                /* dont error if this is a duplicated parameter of a generated canonical constructor
                 * as we should have issued an error for the duplicated fields
                 */
                if (location.kind != MTH ||
                        ((sym.owner.flags_field & GENERATEDCONSTR) == 0) ||
                        ((sym.owner.flags_field & RECORD) == 0)) {
                    log.error(pos,
                            Errors.AlreadyDefined(kindName(sym),
                                    sym,
                                    kindName(sym.location()),
                                    sym.location()));
                }
            }
        }
    }

    
Report array/varargs duplicate declaration
/** Report array/varargs duplicate declaration
     */
    void varargsDuplicateError(DiagnosticPosition pos, Symbol sym1, Symbol sym2) {
        if (!sym1.type.isErroneous() && !sym2.type.isErroneous()) {
            log.error(pos, Errors.ArrayAndVarargs(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.
/** 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) {
        for (Symbol sym : s.getSymbolsByName(v.name)) {
            if (sym.owner != v.owner) break;
            if (sym.kind == VAR &&
                sym.owner.kind.matches(KindSelector.VAL_MTH) &&
                v.name != names.error) {
                duplicateError(pos, 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.
/** 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) {
        for (Symbol sym : s.getSymbolsByName(c.name)) {
            if (sym.owner != c.owner) break;
            if (sym.kind == TYP && !sym.type.hasTag(TYPEVAR) &&
                sym.owner.kind.matches(KindSelector.VAL_MTH) &&
                c.name != names.error) {
                duplicateError(pos, 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.
/** 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 (Symbol sym : s.getSymbolsByName(name, NON_RECURSIVE)) {
            if (sym.kind == TYP && sym.name != names.error) {
                duplicateError(pos, 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
 **************************************************************************/


    private Map<Pair<Name, Name>, Integer> localClassNameIndexes = new HashMap<>();

    
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 /** Return name of local class.
     *  This is of the form   {@code <enclClass> $ n <classname> }
     *  where
     *    enclClass is the flat name of the enclosing class,
     *    classname is the simple name of the local class
     */
    public Name localClassName(ClassSymbol c) {
        Name enclFlatname = c.owner.enclClass().flatname;
        String enclFlatnameStr = enclFlatname.toString();
        Pair<Name, Name> key = new Pair<>(enclFlatname, c.name);
        Integer index = localClassNameIndexes.get(key);
        for (int i = (index == null) ? 1 : index; ; i++) {
            Name flatname = names.fromString(enclFlatnameStr
                    + syntheticNameChar + i + c.name);
            if (getCompiled(c.packge().modle, flatname) == null) {
                localClassNameIndexes.put(key, i + 1);
                return flatname;
            }
        }
    }

    public void clearLocalClassNameIndexes(ClassSymbol c) {
        if (c.owner != null && c.owner.kind != NIL) {
            localClassNameIndexes.remove(new Pair<>(
                    c.owner.enclClass().flatname, c.name));
        }
    }

    public void newRound() {
        compiled.clear();
        localClassNameIndexes.clear();
    }

    public void clear() {
        deprecationHandler.clear();
        removalHandler.clear();
        uncheckedHandler.clear();
        sunApiHandler.clear();
    }

    public void putCompiled(ClassSymbol csym) {
        compiled.put(Pair.of(csym.packge().modle, csym.flatname), csym);
    }

    public ClassSymbol getCompiled(ClassSymbol csym) {
        return compiled.get(Pair.of(csym.packge().modle, csym.flatname));
    }

    public ClassSymbol getCompiled(ModuleSymbol msym, Name flatname) {
        return compiled.get(Pair.of(msym, flatname));
    }

    public void removeCompiled(ClassSymbol csym) {
        compiled.remove(Pair.of(csym.packge().modle, csym.flatname));
    }

/* *************************************************************************
 * Type Checking
 **************************************************************************/

    
A check context is an object that can be used to perform compatibility
checks - depending on the check context, meaning of 'compatibility' might
vary significantly.
/**
     * A check context is an object that can be used to perform compatibility
     * checks - depending on the check context, meaning of 'compatibility' might
     * vary significantly.
     */
    public interface CheckContext {
        
Is type 'found' compatible with type 'req' in given context
/**
         * Is type 'found' compatible with type 'req' in given context
         */
        boolean compatible(Type found, Type req, Warner warn);
        
Report a check error
/**
         * Report a check error
         */
        void report(DiagnosticPosition pos, JCDiagnostic details);
        
Obtain a warner for this check context
/**
         * Obtain a warner for this check context
         */
        public Warner checkWarner(DiagnosticPosition pos, Type found, Type req);

        public InferenceContext inferenceContext();

        public DeferredAttr.DeferredAttrContext deferredAttrContext();
    }

    
This class represent a check context that is nested within another check
context - useful to check sub-expressions. The default behavior simply
redirects all method calls to the enclosing check context leveraging
the forwarding pattern.
/**
     * This class represent a check context that is nested within another check
     * context - useful to check sub-expressions. The default behavior simply
     * redirects all method calls to the enclosing check context leveraging
     * the forwarding pattern.
     */
    static class NestedCheckContext implements CheckContext {
        CheckContext enclosingContext;

        NestedCheckContext(CheckContext enclosingContext) {
            this.enclosingContext = enclosingContext;
        }

        public boolean compatible(Type found, Type req, Warner warn) {
            return enclosingContext.compatible(found, req, warn);
        }

        public void report(DiagnosticPosition pos, JCDiagnostic details) {
            enclosingContext.report(pos, details);
        }

        public Warner checkWarner(DiagnosticPosition pos, Type found, Type req) {
            return enclosingContext.checkWarner(pos, found, req);
        }

        public InferenceContext inferenceContext() {
            return enclosingContext.inferenceContext();
        }

        public DeferredAttrContext deferredAttrContext() {
            return enclosingContext.deferredAttrContext();
        }
    }

    
Check context to be used when evaluating assignment/return statements
/**
     * Check context to be used when evaluating assignment/return statements
     */
    CheckContext basicHandler = new CheckContext() {
        public void report(DiagnosticPosition pos, JCDiagnostic details) {
            log.error(pos, Errors.ProbFoundReq(details));
        }
        public boolean compatible(Type found, Type req, Warner warn) {
            return types.isAssignable(found, req, warn);
        }

        public Warner checkWarner(DiagnosticPosition pos, Type found, Type req) {
            return convertWarner(pos, found, req);
        }

        public InferenceContext inferenceContext() {
            return infer.emptyContext;
        }

        public DeferredAttrContext deferredAttrContext() {
            return deferredAttr.emptyDeferredAttrContext;
        }

        @Override
        public String toString() {
            return "CheckContext: basicHandler";
        }
    };

    
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.
/** 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.
     */
    public Type checkType(DiagnosticPosition pos, Type found, Type req) {
        return checkType(pos, found, req, basicHandler);
    }

    Type checkType(final DiagnosticPosition pos, final Type found, final Type req, final CheckContext checkContext) {
        final InferenceContext inferenceContext = checkContext.inferenceContext();
        if (inferenceContext.free(req) || inferenceContext.free(found)) {
            inferenceContext.addFreeTypeListener(List.of(req, found),
                    solvedContext -> checkType(pos, solvedContext.asInstType(found), solvedContext.asInstType(req), checkContext));
        }
        if (req.hasTag(ERROR))
            return req;
        if (req.hasTag(NONE))
            return found;
        if (checkContext.compatible(found, req, checkContext.checkWarner(pos, found, req))) {
            return found;
        } else {
            if (found.isNumeric() && req.isNumeric()) {
                checkContext.report(pos, diags.fragment(Fragments.PossibleLossOfPrecision(found, req)));
                return types.createErrorType(found);
            }
            checkContext.report(pos, diags.fragment(Fragments.InconvertibleTypes(found, req)));
            return types.createErrorType(found);
        }
    }

    
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.
/** 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) {
        return checkCastable(pos, found, req, basicHandler);
    }
    Type checkCastable(DiagnosticPosition pos, Type found, Type req, CheckContext checkContext) {
        if (types.isCastable(found, req, castWarner(pos, found, req))) {
            return req;
        } else {
            checkContext.report(pos, diags.fragment(Fragments.InconvertibleTypes(found, req)));
            return types.createErrorType(found);
        }
    }

    
Check for redundant casts (i.e. where source type is a subtype of target type)
The problem should only be reported for non-292 cast
/** Check for redundant casts (i.e. where source type is a subtype of target type)
     * The problem should only be reported for non-292 cast
     */
    public void checkRedundantCast(Env<AttrContext> env, final JCTypeCast tree) {
        if (!tree.type.isErroneous()
                && types.isSameType(tree.expr.type, tree.clazz.type)
                && !(ignoreAnnotatedCasts && TreeInfo.containsTypeAnnotation(tree.clazz))
                && !is292targetTypeCast(tree)) {
            deferredLintHandler.report(() -> {
                if (lint.isEnabled(LintCategory.CAST))
                    log.warning(LintCategory.CAST,
                            tree.pos(), Warnings.RedundantCast(tree.clazz.type));
            });
        }
    }
    //where
        private boolean is292targetTypeCast(JCTypeCast tree) {
            boolean is292targetTypeCast = false;
            JCExpression expr = TreeInfo.skipParens(tree.expr);
            if (expr.hasTag(APPLY)) {
                JCMethodInvocation apply = (JCMethodInvocation)expr;
                Symbol sym = TreeInfo.symbol(apply.meth);
                is292targetTypeCast = sym != null &&
                    sym.kind == MTH &&
                    (sym.flags() & HYPOTHETICAL) != 0;
            }
            return is292targetTypeCast;
        }

        private static final boolean ignoreAnnotatedCasts = true;

    
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 a The type that should be bounded by bs. @param bound The bound. /** Check that a type is within some bounds.
     *
     *  Used in TypeApply to verify that, e.g., X in {@code V<X>} is a valid
     *  type argument.
     *  @param a             The type that should be bounded by bs.
     *  @param bound         The bound.
     */
    private boolean checkExtends(Type a, Type bound) {
         if (a.isUnbound()) {
             return true;
         } else if (!a.hasTag(WILDCARD)) {
             a = types.cvarUpperBound(a);
             return types.isSubtype(a, bound);
         } else if (a.isExtendsBound()) {
             return types.isCastable(bound, types.wildUpperBound(a), types.noWarnings);
         } else if (a.isSuperBound()) {
             return !types.notSoftSubtype(types.wildLowerBound(a), bound);
         }
         return true;
     }

    
Check that type is different from 'void'.
 @param pos           Position to be used for error reporting.
 @param t             The type to be checked.
/** 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.hasTag(VOID)) {
            log.error(pos, Errors.VoidNotAllowedHere);
            return types.createErrorType(t);
        } else {
            return t;
        }
    }

    Type checkClassOrArrayType(DiagnosticPosition pos, Type t) {
        if (!t.hasTag(CLASS) && !t.hasTag(ARRAY) && !t.hasTag(ERROR)) {
            return typeTagError(pos,
                                diags.fragment(Fragments.TypeReqClassArray),
                                asTypeParam(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.
/** 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.hasTag(CLASS) && !t.hasTag(ERROR)) {
            return typeTagError(pos,
                                diags.fragment(Fragments.TypeReqClass),
                                asTypeParam(t));
        } else {
            return t;
        }
    }
    //where
        private Object asTypeParam(Type t) {
            return (t.hasTag(TYPEVAR))
                                    ? diags.fragment(Fragments.TypeParameter(t))
                                    : t;
        }

    
Check that type is a valid qualifier for a constructor reference expression
/** Check that type is a valid qualifier for a constructor reference expression
     */
    Type checkConstructorRefType(DiagnosticPosition pos, Type t) {
        t = checkClassOrArrayType(pos, t);
        if (t.hasTag(CLASS)) {
            if ((t.tsym.flags() & (ABSTRACT | INTERFACE)) != 0) {
                log.error(pos, Errors.AbstractCantBeInstantiated(t.tsym));
                t = types.createErrorType(t);
            } else if ((t.tsym.flags() & ENUM) != 0) {
                log.error(pos, Errors.EnumCantBeInstantiated);
                t = types.createErrorType(t);
            } else {
                t = checkClassType(pos, t, true);
            }
        } else if (t.hasTag(ARRAY)) {
            if (!types.isReifiable(((ArrayType)t).elemtype)) {
                log.error(pos, Errors.GenericArrayCreation);
                t = types.createErrorType(t);
            }
        }
        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.
/** 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.hasTag(WILDCARD))
                    return typeTagError(pos,
                                        diags.fragment(Fragments.TypeReqExact),
                                        args.head);
                args = args.tail;
            }
        }
        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.
/** 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) {
        if (t.isReference())
            return t;
        else
            return typeTagError(pos,
                                diags.fragment(Fragments.TypeReqRef),
                                t);
    }

    
Check that each type is a reference type, i.e. a class, interface or array type
 or a type variable.
 @param trees         Original trees, used for error reporting.
 @param types         The types to be checked.
/** Check that each type is a reference type, i.e. a class, interface or array type
     *  or a type variable.
     *  @param trees         Original trees, used for error reporting.
     *  @param types         The types to be checked.
     */
    List<Type> checkRefTypes(List<JCExpression> trees, List<Type> types) {
        List<JCExpression> tl = trees;
        for (List<Type> l = types; l.nonEmpty(); l = l.tail) {
            l.head = checkRefType(tl.head.pos(), l.head);
            tl = tl.tail;
        }
        return types;
    }

    
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.
/** 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) {
        if (t.isReference() || t.hasTag(BOT))
            return t;
        else
            return typeTagError(pos,
                                diags.fragment(Fragments.TypeReqRef),
                                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.
/** 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,
                      Errors.IllegalCombinationOfModifiers(asFlagSet(TreeInfo.firstFlag(flags & set1)),
                                                           asFlagSet(TreeInfo.firstFlag(flags & set2))));
            return false;
        } else
            return true;
    }

    
Check that usage of diamond operator is correct (i.e. diamond should not
be used with non-generic classes or in anonymous class creation expressions)
/** Check that usage of diamond operator is correct (i.e. diamond should not
     * be used with non-generic classes or in anonymous class creation expressions)
     */
    Type checkDiamond(JCNewClass tree, Type t) {
        if (!TreeInfo.isDiamond(tree) ||
                t.isErroneous()) {
            return checkClassType(tree.clazz.pos(), t, true);
        } else {
            if (tree.def != null && !Feature.DIAMOND_WITH_ANONYMOUS_CLASS_CREATION.allowedInSource(source)) {
                log.error(DiagnosticFlag.SOURCE_LEVEL, tree.clazz.pos(),
                        Errors.CantApplyDiamond1(t, Feature.DIAMOND_WITH_ANONYMOUS_CLASS_CREATION.fragment(source.name)));
            }
            if (t.tsym.type.getTypeArguments().isEmpty()) {
                log.error(tree.clazz.pos(),
                          Errors.CantApplyDiamond1(t,
                                                   Fragments.DiamondNonGeneric(t)));
                return types.createErrorType(t);
            } else if (tree.typeargs != null &&
                    tree.typeargs.nonEmpty()) {
                log.error(tree.clazz.pos(),
                          Errors.CantApplyDiamond1(t,
                                                   Fragments.DiamondAndExplicitParams(t)));
                return types.createErrorType(t);
            } else {
                return t;
            }
        }
    }

    
Check that the type inferred using the diamond operator does not contain
 non-denotable types such as captured types or intersection types.
 @param t the type inferred using the diamond operator
 @return  the (possibly empty) list of non-denotable types.
/** Check that the type inferred using the diamond operator does not contain
     *  non-denotable types such as captured types or intersection types.
     *  @param t the type inferred using the diamond operator
     *  @return  the (possibly empty) list of non-denotable types.
     */
    List<Type> checkDiamondDenotable(ClassType t) {
        ListBuffer<Type> buf = new ListBuffer<>();
        for (Type arg : t.allparams()) {
            if (!checkDenotable(arg)) {
                buf.append(arg);
            }
        }
        return buf.toList();
    }

    public boolean checkDenotable(Type t) {
        return denotableChecker.visit(t, null);
    }
        // where

        
diamondTypeChecker: A type visitor that descends down the given type looking for non-denotable
 types. The visit methods return false as soon as a non-denotable type is encountered and true
 otherwise.
/** diamondTypeChecker: A type visitor that descends down the given type looking for non-denotable
         *  types. The visit methods return false as soon as a non-denotable type is encountered and true
         *  otherwise.
         */
        private static final Types.SimpleVisitor<Boolean, Void> denotableChecker = new Types.SimpleVisitor<Boolean, Void>() {
            @Override
            public Boolean visitType(Type t, Void s) {
                return true;
            }
            @Override
            public Boolean visitClassType(ClassType t, Void s) {
                if (t.isUnion() || t.isIntersection()) {
                    return false;
                }
                for (Type targ : t.allparams()) {
                    if (!visit(targ, s)) {
                        return false;
                    }
                }
                return true;
            }

            @Override
            public Boolean visitTypeVar(TypeVar t, Void s) {
                /* Any type variable mentioned in the inferred type must have been declared as a type parameter
                  (i.e cannot have been produced by inference (18.4))
                */
                return (t.tsym.flags() & SYNTHETIC) == 0;
            }

            @Override
            public Boolean visitCapturedType(CapturedType t, Void s) {
                /* Any type variable mentioned in the inferred type must have been declared as a type parameter
                  (i.e cannot have been produced by capture conversion (5.1.10))
                */
                return false;
            }

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

            @Override
            public Boolean visitWildcardType(WildcardType t, Void s) {
                return visit(t.type, s);
            }
        };

    void checkVarargsMethodDecl(Env<AttrContext> env, JCMethodDecl tree) {
        MethodSymbol m = tree.sym;
        boolean hasTrustMeAnno = m.attribute(syms.trustMeType.tsym) != null;
        Type varargElemType = null;
        if (m.isVarArgs()) {
            varargElemType = types.elemtype(tree.params.last().type);
        }
        if (hasTrustMeAnno && !isTrustMeAllowedOnMethod(m)) {
            if (varargElemType != null) {
                JCDiagnostic msg = Feature.PRIVATE_SAFE_VARARGS.allowedInSource(source) ?
                        diags.fragment(Fragments.VarargsTrustmeOnVirtualVarargs(m)) :
                        diags.fragment(Fragments.VarargsTrustmeOnVirtualVarargsFinalOnly(m));
                log.error(tree,
                          Errors.VarargsInvalidTrustmeAnno(syms.trustMeType.tsym,
                                                           msg));
            } else {
                log.error(tree,
                          Errors.VarargsInvalidTrustmeAnno(syms.trustMeType.tsym,
                                                           Fragments.VarargsTrustmeOnNonVarargsMeth(m)));
            }
        } else if (hasTrustMeAnno && varargElemType != null &&
                            types.isReifiable(varargElemType)) {
            warnUnsafeVararg(tree, Warnings.VarargsRedundantTrustmeAnno(
                                syms.trustMeType.tsym,
                                diags.fragment(Fragments.VarargsTrustmeOnReifiableVarargs(varargElemType))));
        }
        else if (!hasTrustMeAnno && varargElemType != null &&
                !types.isReifiable(varargElemType)) {
            warnUnchecked(tree.params.head.pos(), Warnings.UncheckedVarargsNonReifiableType(varargElemType));
        }
    }
    //where
        private boolean isTrustMeAllowedOnMethod(Symbol s) {
            return (s.flags() & VARARGS) != 0 &&
                (s.isConstructor() ||
                    (s.flags() & (STATIC | FINAL |
                                  (Feature.PRIVATE_SAFE_VARARGS.allowedInSource(source) ? PRIVATE : 0) )) != 0);
        }

    Type checkLocalVarType(DiagnosticPosition pos, Type t, Name name) {
        //check that resulting type is not the null type
        if (t.hasTag(BOT)) {
            log.error(pos, Errors.CantInferLocalVarType(name, Fragments.LocalCantInferNull));
            return types.createErrorType(t);
        } else if (t.hasTag(VOID)) {
            log.error(pos, Errors.CantInferLocalVarType(name, Fragments.LocalCantInferVoid));
            return types.createErrorType(t);
        }

        //upward project the initializer type
        return types.upward(t, types.captures(t));
    }

    Type checkMethod(final Type mtype,
            final Symbol sym,
            final Env<AttrContext> env,
            final List<JCExpression> argtrees,
            final List<Type> argtypes,
            final boolean useVarargs,
            InferenceContext inferenceContext) {
        // System.out.println("call   : " + env.tree);
        // System.out.println("method : " + owntype);
        // System.out.println("actuals: " + argtypes);
        if (inferenceContext.free(mtype)) {
            inferenceContext.addFreeTypeListener(List.of(mtype),
                    solvedContext -> checkMethod(solvedContext.asInstType(mtype), sym, env, argtrees, argtypes, useVarargs, solvedContext));
            return mtype;
        }
        Type owntype = mtype;
        List<Type> formals = owntype.getParameterTypes();
        List<Type> nonInferred = sym.type.getParameterTypes();
        if (nonInferred.length() != formals.length()) nonInferred = formals;
        Type last = useVarargs ? formals.last() : null;
        if (sym.name == names.init && sym.owner == syms.enumSym) {
            formals = formals.tail.tail;
            nonInferred = nonInferred.tail.tail;
        }
        if ((sym.flags() & ANONCONSTR_BASED) != 0) {
            formals = formals.tail;
            nonInferred = nonInferred.tail;
        }
        List<JCExpression> args = argtrees;
        if (args != null) {
            //this is null when type-checking a method reference
            while (formals.head != last) {
                JCTree arg = args.head;
                Warner warn = convertWarner(arg.pos(), arg.type, nonInferred.head);
                assertConvertible(arg, arg.type, formals.head, warn);
                args = args.tail;
                formals = formals.tail;
                nonInferred = nonInferred.tail;
            }
            if (useVarargs) {
                Type varArg = types.elemtype(last);
                while (args.tail != null) {
                    JCTree arg = args.head;
                    Warner warn = convertWarner(arg.pos(), arg.type, varArg);
                    assertConvertible(arg, arg.type, varArg, warn);
                    args = args.tail;
                }
            } else if ((sym.flags() & (VARARGS | SIGNATURE_POLYMORPHIC)) == VARARGS) {
                // non-varargs call to varargs method
                Type varParam = owntype.getParameterTypes().last();
                Type lastArg = argtypes.last();
                if (types.isSubtypeUnchecked(lastArg, types.elemtype(varParam)) &&
                    !types.isSameType(types.erasure(varParam), types.erasure(lastArg)))
                    log.warning(argtrees.last().pos(),
                                Warnings.InexactNonVarargsCall(types.elemtype(varParam),varParam));
            }
        }
        if (useVarargs) {
            Type argtype = owntype.getParameterTypes().last();
            if (!types.isReifiable(argtype) &&
                (sym.baseSymbol().attribute(syms.trustMeType.tsym) == null ||
                 !isTrustMeAllowedOnMethod(sym))) {
                warnUnchecked(env.tree.pos(), Warnings.UncheckedGenericArrayCreation(argtype));
            }
            TreeInfo.setVarargsElement(env.tree, types.elemtype(argtype));
         }
         return owntype;
    }
    //where
    private void assertConvertible(JCTree tree, Type actual, Type formal, Warner warn) {
        if (types.isConvertible(actual, formal, warn))
            return;

        if (formal.isCompound()
            && types.isSubtype(actual, types.supertype(formal))
            && types.isSubtypeUnchecked(actual, types.interfaces(formal), warn))
            return;
    }

    
Check that type 't' is a valid instantiation of a generic class
(see JLS 4.5)
Params:
t – class type to be checked
Returns:
true if 't' is well-formed/**
     * Check that type 't' is a valid instantiation of a generic class
     * (see JLS 4.5)
     *
     * @param t class type to be checked
     * @return true if 't' is well-formed
     */
    public boolean checkValidGenericType(Type t) {
        return firstIncompatibleTypeArg(t) == null;
    }
    //WHERE
        private Type firstIncompatibleTypeArg(Type type) {
            List<Type> formals = type.tsym.type.allparams();
            List<Type> actuals = type.allparams();
            List<Type> args = type.getTypeArguments();
            List<Type> forms = type.tsym.type.getTypeArguments();
            ListBuffer<Type> bounds_buf = new ListBuffer<>();

            // For matching pairs of actual argument types `a' and
            // formal type parameters with declared bound `b' ...
            while (args.nonEmpty() && forms.nonEmpty()) {
                // exact type arguments needs to know their
                // bounds (for upper and lower bound
                // calculations).  So we create new bounds where
                // type-parameters are replaced with actuals argument types.
                bounds_buf.append(types.subst(forms.head.getUpperBound(), formals, actuals));
                args = args.tail;
                forms = forms.tail;
            }

            args = type.getTypeArguments();
            List<Type> tvars_cap = types.substBounds(formals,
                                      formals,
                                      types.capture(type).allparams());
            while (args.nonEmpty() && tvars_cap.nonEmpty()) {
                // Let the actual arguments know their bound
                args.head.withTypeVar((TypeVar)tvars_cap.head);
                args = args.tail;
                tvars_cap = tvars_cap.tail;
            }

            args = type.getTypeArguments();
            List<Type> bounds = bounds_buf.toList();

            while (args.nonEmpty() && bounds.nonEmpty()) {
                Type actual = args.head;
                if (!isTypeArgErroneous(actual) &&
                        !bounds.head.isErroneous() &&
                        !checkExtends(actual, bounds.head)) {
                    return args.head;
                }
                args = args.tail;
                bounds = bounds.tail;
            }

            args = type.getTypeArguments();
            bounds = bounds_buf.toList();

            for (Type arg : types.capture(type).getTypeArguments()) {
                if (arg.hasTag(TYPEVAR) &&
                        arg.getUpperBound().isErroneous() &&
                        !bounds.head.isErroneous() &&
                        !isTypeArgErroneous(args.head)) {
                    return args.head;
                }
                bounds = bounds.tail;
                args = args.tail;
            }

            return null;
        }
        //where
        boolean isTypeArgErroneous(Type t) {
            return isTypeArgErroneous.visit(t);
        }

        Types.UnaryVisitor<Boolean> isTypeArgErroneous = new Types.UnaryVisitor<Boolean>() {
            public Boolean visitType(Type t, Void s) {
                return t.isErroneous();
            }
            @Override
            public Boolean visitTypeVar(TypeVar t, Void s) {
                return visit(t.getUpperBound());
            }
            @Override
            public Boolean visitCapturedType(CapturedType t, Void s) {
                return visit(t.getUpperBound()) ||
                        visit(t.getLowerBound());
            }
            @Override
            public Boolean visitWildcardType(WildcardType t, Void s) {
                return visit(t.type);
            }
        };

    
Check that given modifiers are legal for given symbol and
 return modifiers together with any implicit modifiers 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.
/** Check that given modifiers are legal for given symbol and
     *  return modifiers together with any implicit modifiers 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 (TreeInfo.isReceiverParam(tree))
                mask = ReceiverParamFlags;
            else 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) {
                if ((sym.owner.flags_field & ANNOTATION) != 0) {
                    mask = AnnotationTypeElementMask;
                    implicit = PUBLIC | ABSTRACT;
                } else if ((flags & (DEFAULT | STATIC | PRIVATE)) != 0) {
                    mask = InterfaceMethodMask;
                    implicit = (flags & PRIVATE) != 0 ? 0 : PUBLIC;
                    if ((flags & DEFAULT) != 0) {
                        implicit |= ABSTRACT;
                    }
                } else {
                    mask = implicit = InterfaceMethodFlags;
                }
            } else if ((sym.owner.flags_field & RECORD) != 0) {
                mask = RecordMethodFlags;
            } else {
                mask = MethodFlags;
            }
            // Imply STRICTFP if owner has STRICTFP set.
            if (((flags|implicit) & Flags.ABSTRACT) == 0 ||
                ((flags) & Flags.DEFAULT) != 0)
                implicit |= sym.owner.flags_field & STRICTFP;
            break;
        case TYP:
            if (sym.isLocal()) {
                mask = (flags & RECORD) != 0 ? LocalRecordFlags : LocalClassFlags;
                if ((flags & RECORD) != 0) {
                    implicit = STATIC;
                    if (sym.owner.kind == TYP) {
                        log.error(pos, Errors.RecordDeclarationNotAllowedInInnerClasses);
                    }
                }
                if ((sym.owner.flags_field & STATIC) == 0 &&
                    (flags & ENUM) != 0) {
                    log.error(pos, Errors.EnumsMustBeStatic);
                }
            } else if (sym.owner.kind == TYP) {
                mask = (flags & RECORD) != 0 ? MemberRecordFlags : MemberClassFlags;
                if (sym.owner.owner.kind == PCK ||
                    (sym.owner.flags_field & STATIC) != 0)
                    mask |= STATIC;
                else if ((flags & ENUM) != 0) {
                    log.error(pos, Errors.EnumsMustBeStatic);
                } else if ((flags & RECORD) != 0) {
                    log.error(pos, Errors.RecordDeclarationNotAllowedInInnerClasses);
                }
                // Nested interfaces and enums are always STATIC (Spec ???)
                if ((flags & (INTERFACE | ENUM | RECORD)) != 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);
            }
            if ((flags & RECORD) != 0) {
                // records can't be declared abstract
                mask &= ~ABSTRACT;
                implicit |= FINAL;
            }
            // Imply STRICTFP if owner has STRICTFP set.
            implicit |= sym.owner.flags_field & STRICTFP;
            break;
        default:
            throw new AssertionError();
        }
        long illegal = flags & ExtendedStandardFlags & ~mask;
        if (illegal != 0) {
            if ((illegal & INTERFACE) != 0) {
                log.error(pos, ((flags & ANNOTATION) != 0) ? Errors.AnnotationDeclNotAllowedHere : Errors.IntfNotAllowedHere);
                mask |= INTERFACE;
            }
            else {
                log.error(pos,
                          Errors.ModNotAllowedHere(asFlagSet(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 | DEFAULT))
                 &&
                 checkDisjoint(pos, flags,
                                STATIC | PRIVATE,
                                DEFAULT)
                 &&
                 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 | ~ExtendedStandardFlags) | 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
 not final.
/** 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.hasTag(CLASSDEF)) return 0;
        class SpecialTreeVisitor extends JCTree.Visitor {
            boolean specialized;
            SpecialTreeVisitor() {
                this.specialized = false;
            }

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

            @Override
            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 attribution
 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.
Visitor method: Validate a type expression, if it is not null, catching
 and reporting any completion failures.
/** 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 attribution
     *  since a class might have a subclass as type parameter bound. E.g:
     *
     *  <pre>{@code
     *  class B<A extends C> { ... }
     *  class C extends B<C> { ... }
     *  }</pre>
     *
     *  and we can't make sure that the bound is already attributed because
     *  of possible cycles.
     *
     * Visitor method: Validate a type expression, if it is not null, catching
     *  and reporting any completion failures.
     */
    void validate(JCTree tree, Env<AttrContext> env) {
        validate(tree, env, true);
    }
    void validate(JCTree tree, Env<AttrContext> env, boolean checkRaw) {
        new Validator(env).validateTree(tree, checkRaw, true);
    }

    
Visitor method: Validate a list of type expressions.
/** Visitor method: Validate a list of type expressions.
     */
    void validate(List<? extends JCTree> trees, Env<AttrContext> env) {
        for (List<? extends JCTree> l = trees; l.nonEmpty(); l = l.tail)
            validate(l.head, env);
    }

    
A visitor class for type validation.
/** A visitor class for type validation.
     */
    class Validator extends JCTree.Visitor {

        boolean checkRaw;
        boolean isOuter;
        Env<AttrContext> env;

        Validator(Env<AttrContext> env) {
            this.env = env;
        }

        @Override
        public void visitTypeArray(JCArrayTypeTree tree) {
            validateTree(tree.elemtype, checkRaw, isOuter);
        }

        @Override
        public void visitTypeApply(JCTypeApply tree) {
            if (tree.type.hasTag(CLASS)) {
                List<JCExpression> args = tree.arguments;
                List<Type> forms = tree.type.tsym.type.getTypeArguments();

                Type incompatibleArg = firstIncompatibleTypeArg(tree.type);
                if (incompatibleArg != null) {
                    for (JCTree arg : tree.arguments) {
                        if (arg.type == incompatibleArg) {
                            log.error(arg, Errors.NotWithinBounds(incompatibleArg, forms.head));
                        }
                        forms = forms.tail;
                     }
                 }

                forms = tree.type.tsym.type.getTypeArguments();

                boolean is_java_lang_Class = tree.type.tsym.flatName() == names.java_lang_Class;

                // For matching pairs of actual argument types `a' and
                // formal type parameters with declared bound `b' ...
                while (args.nonEmpty() && forms.nonEmpty()) {
                    validateTree(args.head,
                            !(isOuter && is_java_lang_Class),
                            false);
                    args = args.tail;
                    forms = forms.tail;
                }

                // Check that this type is either fully parameterized, or
                // not parameterized at all.
                if (tree.type.getEnclosingType().isRaw())
                    log.error(tree.pos(), Errors.ImproperlyFormedTypeInnerRawParam);
                if (tree.clazz.hasTag(SELECT))
                    visitSelectInternal((JCFieldAccess)tree.clazz);
            }
        }

        @Override
        public void visitTypeParameter(JCTypeParameter tree) {
            validateTrees(tree.bounds, true, isOuter);
            checkClassBounds(tree.pos(), tree.type);
        }

        @Override
        public void visitWildcard(JCWildcard tree) {
            if (tree.inner != null)
                validateTree(tree.inner, true, isOuter);
        }

        @Override
        public void visitSelect(JCFieldAccess tree) {
            if (tree.type.hasTag(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(), Errors.ImproperlyFormedTypeParamMissing);
            }
        }

        public void visitSelectInternal(JCFieldAccess tree) {
            if (tree.type.tsym.isStatic() &&
                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(), Errors.CantSelectStaticClassFromParamType);
            } else {
                // otherwise validate the rest of the expression
                tree.selected.accept(this);
            }
        }

        @Override
        public void visitAnnotatedType(JCAnnotatedType tree) {
            tree.underlyingType.accept(this);
        }

        @Override
        public void visitTypeIdent(JCPrimitiveTypeTree that) {
            if (that.type.hasTag(TypeTag.VOID)) {
                log.error(that.pos(), Errors.VoidNotAllowedHere);
            }
            super.visitTypeIdent(that);
        }

        
Default visitor method: do nothing.
/** Default visitor method: do nothing.
         */
        @Override
        public void visitTree(JCTree tree) {
        }

        public void validateTree(JCTree tree, boolean checkRaw, boolean isOuter) {
            if (tree != null) {
                boolean prevCheckRaw = this.checkRaw;
                this.checkRaw = checkRaw;
                this.isOuter = isOuter;

                try {
                    tree.accept(this);
                    if (checkRaw)
                        checkRaw(tree, env);
                } catch (CompletionFailure ex) {
                    completionError(tree.pos(), ex);
                } finally {
                    this.checkRaw = prevCheckRaw;
                }
            }
        }

        public void validateTrees(List<? extends JCTree> trees, boolean checkRaw, boolean isOuter) {
            for (List<? extends JCTree> l = trees; l.nonEmpty(); l = l.tail)
                validateTree(l.head, checkRaw, isOuter);
        }
    }

    void checkRaw(JCTree tree, Env<AttrContext> env) {
        if (lint.isEnabled(LintCategory.RAW) &&
            tree.type.hasTag(CLASS) &&
            !TreeInfo.isDiamond(tree) &&
            !withinAnonConstr(env) &&
            tree.type.isRaw()) {
            log.warning(LintCategory.RAW,
                    tree.pos(), Warnings.RawClassUse(tree.type, tree.type.tsym.type));
        }
    }
    //where
        private boolean withinAnonConstr(Env<AttrContext> env) {
            return env.enclClass.name.isEmpty() &&
                    env.enclMethod != null && env.enclMethod.name == names.init;
        }

/* *************************************************************************
 * 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?
/** 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?
/** 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.
/** 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.
/** 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.
/** 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.
/** 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.
/** 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?
/** 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?
/** Is exc an exception type that need not be declared?
     */
    boolean isUnchecked(Type exc) {
        return
            (exc.hasTag(TYPEVAR)) ? isUnchecked(types.supertype(exc)) :
            (exc.hasTag(CLASS)) ? isUnchecked((ClassSymbol)exc.tsym) :
            exc.hasTag(BOT);
    }

    boolean isChecked(Type exc) {
        return !isUnchecked(exc);
    }

    
Same, but handling completion failures.
/** 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?
/** 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.
/** 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.
/** 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 customized "cannot override" error message.
 @param m      The overriding method.
 @param other  The overridden method.
 @return       An internationalized string.
/** A customized "cannot override" error message.
     *  @param m      The overriding method.
     *  @param other  The overridden method.
     *  @return       An internationalized string.
     */
    Fragment cannotOverride(MethodSymbol m, MethodSymbol other) {
        Symbol mloc = m.location();
        Symbol oloc = other.location();

        if ((other.owner.flags() & INTERFACE) == 0)
            return Fragments.CantOverride(m, mloc, other, oloc);
        else if ((m.owner.flags() & INTERFACE) == 0)
            return Fragments.CantImplement(m, mloc, other, oloc);
        else
            return Fragments.ClashesWith(m, mloc, other, oloc);
    }

    
A customized "override" warning message.
 @param m      The overriding method.
 @param other  The overridden method.
 @return       An internationalized string.
/** A customized "override" warning message.
     *  @param m      The overriding method.
     *  @param other  The overridden method.
     *  @return       An internationalized string.
     */
    Fragment uncheckedOverrides(MethodSymbol m, MethodSymbol other) {
        Symbol mloc = m.location();
        Symbol oloc = other.location();

        if ((other.owner.flags() & INTERFACE) == 0)
            return Fragments.UncheckedOverride(m, mloc, other, oloc);
        else if ((m.owner.flags() & INTERFACE) == 0)
            return Fragments.UncheckedImplement(m, mloc, other, oloc);
        else
            return Fragments.UncheckedClashWith(m, mloc, other, oloc);
    }

    
A customized "override" warning message.
 @param m      The overriding method.
 @param other  The overridden method.
 @return       An internationalized string.
/** A customized "override" warning message.
     *  @param m      The overriding method.
     *  @param other  The overridden method.
     *  @return       An internationalized string.
     */
    Fragment varargsOverrides(MethodSymbol m, MethodSymbol other) {
        Symbol mloc = m.location();
        Symbol oloc = other.location();

        if ((other.owner.flags() & INTERFACE) == 0)
            return Fragments.VarargsOverride(m, mloc, other, oloc);
        else  if ((m.owner.flags() & INTERFACE) == 0)
            return Fragments.VarargsImplement(m, mloc, other, oloc);
        else
            return Fragments.VarargsClashWith(m, mloc, other, oloc);
    }

    
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.
/** 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),
                      Errors.OverrideStatic(cannotOverride(m, other)));
            m.flags_field |= BAD_OVERRIDE;
            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),
                      Errors.OverrideMeth(cannotOverride(m, other),
                                          asFlagSet(other.flags() & (FINAL | STATIC))));
            m.flags_field |= BAD_OVERRIDE;
            return;
        }

        if ((m.owner.flags() & ANNOTATION) != 0) {
            // handled in validateAnnotationMethod
            return;
        }

        // Error if overriding method has weaker access (JLS 8.4.6.3).
        if (protection(m.flags()) > protection(other.flags())) {
            log.error(TreeInfo.diagnosticPositionFor(m, tree),
                      (other.flags() & AccessFlags) == 0 ?
                              Errors.OverrideWeakerAccess(cannotOverride(m, other),
                                                          "package") :
                              Errors.OverrideWeakerAccess(cannotOverride(m, other),
                                                          asFlagSet(other.flags() & AccessFlags)));
            m.flags_field |= BAD_OVERRIDE;
            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.clear();
        boolean resultTypesOK =
            types.returnTypeSubstitutable(mt, ot, otres, overrideWarner);
        if (!resultTypesOK) {
            if ((m.flags() & STATIC) != 0 && (other.flags() & STATIC) != 0) {
                log.error(TreeInfo.diagnosticPositionFor(m, tree),
                          Errors.OverrideIncompatibleRet(Fragments.CantHide(m, m.location(), other,
                                        other.location()), mtres, otres));
                m.flags_field |= BAD_OVERRIDE;
            } else {
                log.error(TreeInfo.diagnosticPositionFor(m, tree),
                          Errors.OverrideIncompatibleRet(cannotOverride(m, other), mtres, otres));
                m.flags_field |= BAD_OVERRIDE;
            }
            return;
        } else if (overrideWarner.hasNonSilentLint(LintCategory.UNCHECKED)) {
            warnUnchecked(TreeInfo.diagnosticPositionFor(m, tree),
                    Warnings.OverrideUncheckedRet(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> unhandledErased = unhandled(mt.getThrownTypes(), types.erasure(otthrown));
        List<Type> unhandledUnerased = unhandled(mt.getThrownTypes(), otthrown);
        if (unhandledErased.nonEmpty()) {
            log.error(TreeInfo.diagnosticPositionFor(m, tree),
                      Errors.OverrideMethDoesntThrow(cannotOverride(m, other), unhandledUnerased.head));
            m.flags_field |= BAD_OVERRIDE;
            return;
        }
        else if (unhandledUnerased.nonEmpty()) {
            warnUnchecked(TreeInfo.diagnosticPositionFor(m, tree),
                          Warnings.OverrideUncheckedThrown(cannotOverride(m, other), unhandledUnerased.head));
            return;
        }

        // Optional warning if varargs don't agree
        if ((((m.flags() ^ other.flags()) & Flags.VARARGS) != 0)
            && lint.isEnabled(LintCategory.OVERRIDES)) {
            log.warning(TreeInfo.diagnosticPositionFor(m, tree),
                        ((m.flags() & Flags.VARARGS) != 0)
                        ? Warnings.OverrideVarargsMissing(varargsOverrides(m, other))
                        : Warnings.OverrideVarargsExtra(varargsOverrides(m, other)));
        }

        // Warn if instance method overrides bridge method (compiler spec ??)
        if ((other.flags() & BRIDGE) != 0) {
            log.warning(TreeInfo.diagnosticPositionFor(m, tree),
                        Warnings.OverrideBridge(uncheckedOverrides(m, other)));
        }

        // Warn if a deprecated method overridden by a non-deprecated one.
        if (!isDeprecatedOverrideIgnorable(other, origin)) {
            Lint prevLint = setLint(lint.augment(m));
            try {
                checkDeprecated(() -> TreeInfo.diagnosticPositionFor(m, tree), m, other);
            } finally {
                setLint(prevLint);
            }
        }
    }
    // 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.hasTag(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.
/** 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.hasTag(CLASS)) return;

        for (Type t1 = sup;
             t1.hasTag(CLASS) && t1.tsym.type.isParameterized();
             t1 = types.supertype(t1)) {
            for (Symbol s1 : t1.tsym.members().getSymbols(NON_RECURSIVE)) {
                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.hasTag(CLASS);
                     t2 = types.supertype(t2)) {
                    for (Symbol s2 : t2.tsym.members().getSymbolsByName(s1.name)) {
                        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,
                                      Errors.ConcreteInheritanceConflict(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.
/** 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,
                                            Type site) {
        if ((site.tsym.flags() & COMPOUND) != 0) {
            // special case for intersections: need to eliminate wildcards in supertypes
            t1 = types.capture(t1);
            t2 = types.capture(t2);
        }
        return firstIncompatibility(pos, t1, t2, site) == null;
    }

    
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.
/** 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(DiagnosticPosition pos, Type t1, Type t2, Type site) {
        Map<TypeSymbol,Type> interfaces1 = new HashMap<>();
        closure(t1, interfaces1);
        Map<TypeSymbol,Type> interfaces2;
        if (t1 == t2)
            interfaces2 = interfaces1;
        else
            closure(t2, interfaces1, interfaces2 = new HashMap<>());

        for (Type t3 : interfaces1.values()) {
            for (Type t4 : interfaces2.values()) {
                Symbol s = firstDirectIncompatibility(pos, t3, t4, site);
                if (s != null) return s;
            }
        }
        return null;
    }

    
Compute all the supertypes of t, indexed by type symbol. /** Compute all the supertypes of t, indexed by type symbol. */
    private void closure(Type t, Map<TypeSymbol,Type> typeMap) {
        if (!t.hasTag(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). /** 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.hasTag(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. /** Return the first method in t2 that conflicts with a method from t1. */
    private Symbol firstDirectIncompatibility(DiagnosticPosition pos, Type t1, Type t2, Type site) {
        for (Symbol s1 : t1.tsym.members().getSymbols(NON_RECURSIVE)) {
            Type st1 = null;
            if (s1.kind != MTH || !s1.isInheritedIn(site.tsym, types) ||
                    (s1.flags() & SYNTHETIC) != 0) continue;
            Symbol impl = ((MethodSymbol)s1).implementation(site.tsym, types, false);
            if (impl != null && (impl.flags() & ABSTRACT) == 0) continue;
            for (Symbol s2 : t2.tsym.members().getSymbolsByName(s1.name)) {
                if (s1 == s2) continue;
                if (s2.kind != MTH || !s2.isInheritedIn(site.tsym, types) ||
                        (s2.flags() & SYNTHETIC) != 0) 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.isPrimitiveOrVoid() &&
                        !rt2.isPrimitiveOrVoid() &&
                        (types.covariantReturnType(rt1, rt2, types.noWarnings) ||
                         types.covariantReturnType(rt2, rt1, types.noWarnings)) ||
                         checkCommonOverriderIn(s1,s2,site);
                    if (!compat) {
                        log.error(pos, Errors.TypesIncompatible(t1, t2,
                                Fragments.IncompatibleDiffRet(s2.name, types.memberType(t2, s2).getParameterTypes())));
                        return s2;
                    }
                } else if (checkNameClash((ClassSymbol)site.tsym, s1, s2) &&
                        !checkCommonOverriderIn(s1, s2, site)) {
                    log.error(pos, Errors.NameClashSameErasureNoOverride(
                            s1.name, types.memberType(site, s1).asMethodType().getParameterTypes(), s1.location(),
                            s2.name, types.memberType(site, s2).asMethodType().getParameterTypes(), s2.location()));
                    return s2;
                }
            }
        }
        return null;
    }
    //WHERE
    boolean checkCommonOverriderIn(Symbol s1, Symbol s2, Type site) {
        Map<TypeSymbol,Type> supertypes = new HashMap<>();
        Type st1 = types.memberType(site, s1);
        Type st2 = types.memberType(site, s2);
        closure(site, supertypes);
        for (Type t : supertypes.values()) {
            for (Symbol s3 : t.tsym.members().getSymbolsByName(s1.name)) {
                if (s3 == s1 || s3 == s2 || s3.kind != MTH || (s3.flags() & (BRIDGE|SYNTHETIC)) != 0) continue;
                Type st3 = types.memberType(site,s3);
                if (types.overrideEquivalent(st3, st1) &&
                        types.overrideEquivalent(st3, st2) &&
                        types.returnTypeSubstitutable(st3, st1) &&
                        types.returnTypeSubstitutable(st3, st2)) {
                    return true;
                }
            }
        }
        return false;
    }

    
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.
/** 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(Env<AttrContext> env, JCMethodDecl 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(), Errors.EnumNoFinalize);
                return;
            }
        for (Type t = origin.type; t.hasTag(CLASS);
             t = types.supertype(t)) {
            if (t != origin.type) {
                checkOverride(tree, t, origin, m);
            }
            for (Type t2 : types.interfaces(t)) {
                checkOverride(tree, t2, origin, m);
            }
        }

        final boolean explicitOverride = m.attribute(syms.overrideType.tsym) != null;
        // Check if this method must override a super method due to being annotated with @Override
        // or by virtue of being a member of a diamond inferred anonymous class. Latter case is to
        // be treated "as if as they were annotated" with @Override.
        boolean mustOverride = explicitOverride ||
                (env.info.isAnonymousDiamond && !m.isConstructor() && !m.isPrivate());
        if (mustOverride && !isOverrider(m)) {
            DiagnosticPosition pos = tree.pos();
            for (JCAnnotation a : tree.getModifiers().annotations) {
                if (a.annotationType.type.tsym == syms.overrideType.tsym) {
                    pos = a.pos();
                    break;
                }
            }
            log.error(pos,
                      explicitOverride ? (m.isStatic() ? Errors.StaticMethodsCannotBeAnnotatedWithOverride : Errors.MethodDoesNotOverrideSuperclass) :
                                Errors.AnonymousDiamondMethodDoesNotOverrideSuperclass(Fragments.DiamondAnonymousMethodsImplicitlyOverride));
        }
    }

    void checkOverride(JCTree tree, Type site, ClassSymbol origin, MethodSymbol m) {
        TypeSymbol c = site.tsym;
        for (Symbol sym : c.members().getSymbolsByName(m.name)) {
            if (m.overrides(sym, origin, types, false)) {
                if ((sym.flags() & ABSTRACT) == 0) {
                    checkOverride(tree, m, (MethodSymbol)sym, origin);
                }
            }
        }
    }

    private Filter<Symbol> equalsHasCodeFilter = s -> MethodSymbol.implementation_filter.accepts(s) &&
            (s.flags() & BAD_OVERRIDE) == 0;

    public void checkClassOverrideEqualsAndHashIfNeeded(DiagnosticPosition pos,
            ClassSymbol someClass) {
        /* At present, annotations cannot possibly have a method that is override
         * equivalent with Object.equals(Object) but in any case the condition is
         * fine for completeness.
         */
        if (someClass == (ClassSymbol)syms.objectType.tsym ||
            someClass.isInterface() || someClass.isEnum() ||
            (someClass.flags() & ANNOTATION) != 0 ||
            (someClass.flags() & ABSTRACT) != 0) return;
        //anonymous inner classes implementing interfaces need especial treatment
        if (someClass.isAnonymous()) {
            List<Type> interfaces =  types.interfaces(someClass.type);
            if (interfaces != null && !interfaces.isEmpty() &&
                interfaces.head.tsym == syms.comparatorType.tsym) return;
        }
        checkClassOverrideEqualsAndHash(pos, someClass);
    }

    private void checkClassOverrideEqualsAndHash(DiagnosticPosition pos,
            ClassSymbol someClass) {
        if (lint.isEnabled(LintCategory.OVERRIDES)) {
            MethodSymbol equalsAtObject = (MethodSymbol)syms.objectType
                    .tsym.members().findFirst(names.equals);
            MethodSymbol hashCodeAtObject = (MethodSymbol)syms.objectType
                    .tsym.members().findFirst(names.hashCode);
            boolean overridesEquals = types.implementation(equalsAtObject,
                someClass, false, equalsHasCodeFilter).owner == someClass;
            boolean overridesHashCode = types.implementation(hashCodeAtObject,
                someClass, false, equalsHasCodeFilter) != hashCodeAtObject;

            if (overridesEquals && !overridesHashCode) {
                log.warning(LintCategory.OVERRIDES, pos,
                            Warnings.OverrideEqualsButNotHashcode(someClass));
            }
        }
    }

    public void checkModuleName (JCModuleDecl tree) {
        Name moduleName = tree.sym.name;
        Assert.checkNonNull(moduleName);
        if (lint.isEnabled(LintCategory.MODULE)) {
            JCExpression qualId = tree.qualId;
            while (qualId != null) {
                Name componentName;
                DiagnosticPosition pos;
                switch (qualId.getTag()) {
                    case SELECT:
                        JCFieldAccess selectNode = ((JCFieldAccess) qualId);
                        componentName = selectNode.name;
                        pos = selectNode.pos();
                        qualId = selectNode.selected;
                        break;
                    case IDENT:
                        componentName = ((JCIdent) qualId).name;
                        pos = qualId.pos();
                        qualId = null;
                        break;
                    default:
                        throw new AssertionError("Unexpected qualified identifier: " + qualId.toString());
                }
                if (componentName != null) {
                    String moduleNameComponentString = componentName.toString();
                    int nameLength = moduleNameComponentString.length();
                    if (nameLength > 0 && Character.isDigit(moduleNameComponentString.charAt(nameLength - 1))) {
                        log.warning(Lint.LintCategory.MODULE, pos, Warnings.PoorChoiceForModuleName(componentName));
                    }
                }
            }
        }
    }

    private boolean checkNameClash(ClassSymbol origin, Symbol s1, Symbol s2) {
        ClashFilter cf = new ClashFilter(origin.type);
        return (cf.accepts(s1) &&
                cf.accepts(s2) &&
                types.hasSameArgs(s1.erasure(types), s2.erasure(types)));
    }


    
Check that all abstract members of given class have definitions.
 @param pos          Position to be used for error reporting.
 @param c            The class.
/** 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) {
        MethodSymbol undef = types.firstUnimplementedAbstract(c);
        if (undef != null) {
            MethodSymbol undef1 =
                new MethodSymbol(undef.flags(), undef.name,
                                 types.memberType(c.type, undef), undef.owner);
            log.error(pos,
                      Errors.DoesNotOverrideAbstract(c, undef1, undef1.location()));
        }
    }

    void checkNonCyclicDecl(JCClassDecl tree) {
        CycleChecker cc = new CycleChecker();
        cc.scan(tree);
        if (!cc.errorFound && !cc.partialCheck) {
            tree.sym.flags_field |= ACYCLIC;
        }
    }

    class CycleChecker extends TreeScanner {

        List<Symbol> seenClasses = List.nil();
        boolean errorFound = false;
        boolean partialCheck = false;

        private void checkSymbol(DiagnosticPosition pos, Symbol sym) {
            if (sym != null && sym.kind == TYP) {
                Env<AttrContext> classEnv = enter.getEnv((TypeSymbol)sym);
                if (classEnv != null) {
                    DiagnosticSource prevSource = log.currentSource();
                    try {
                        log.useSource(classEnv.toplevel.sourcefile);
                        scan(classEnv.tree);
                    }
                    finally {
                        log.useSource(prevSource.getFile());
                    }
                } else if (sym.kind == TYP) {
                    checkClass(pos, sym, List.nil());
                }
            } else {
                //not completed yet
                partialCheck = true;
            }
        }

        @Override
        public void visitSelect(JCFieldAccess tree) {
            super.visitSelect(tree);
            checkSymbol(tree.pos(), tree.sym);
        }

        @Override
        public void visitIdent(JCIdent tree) {
            checkSymbol(tree.pos(), tree.sym);
        }

        @Override
        public void visitTypeApply(JCTypeApply tree) {
            scan(tree.clazz);
        }

        @Override
        public void visitTypeArray(JCArrayTypeTree tree) {
            scan(tree.elemtype);
        }

        @Override
        public void visitClassDef(JCClassDecl tree) {
            List<JCTree> supertypes = List.nil();
            if (tree.getExtendsClause() != null) {
                supertypes = supertypes.prepend(tree.getExtendsClause());
            }
            if (tree.getImplementsClause() != null) {
                for (JCTree intf : tree.getImplementsClause()) {
                    supertypes = supertypes.prepend(intf);
                }
            }
            checkClass(tree.pos(), tree.sym, supertypes);
        }

        void checkClass(DiagnosticPosition pos, Symbol c, List<JCTree> supertypes) {
            if ((c.flags_field & ACYCLIC) != 0)
                return;
            if (seenClasses.contains(c)) {
                errorFound = true;
                noteCyclic(pos, (ClassSymbol)c);
            } else if (!c.type.isErroneous()) {
                try {
                    seenClasses = seenClasses.prepend(c);
                    if (c.type.hasTag(CLASS)) {
                        if (supertypes.nonEmpty()) {
                            scan(supertypes);
                        }
                        else {
                            ClassType ct = (ClassType)c.type;
                            if (ct.supertype_field == null ||
                                    ct.interfaces_field == null) {
                                //not completed yet
                                partialCheck = true;
                                return;
                            }
                            checkSymbol(pos, ct.supertype_field.tsym);
                            for (Type intf : ct.interfaces_field) {
                                checkSymbol(pos, intf.tsym);
                            }
                        }
                        if (c.owner.kind == TYP) {
                            checkSymbol(pos, c.owner);
                        }
                    }
                } finally {
                    seenClasses = seenClasses.tail;
                }
            }
        }
    }

    
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.
/** 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, List.nil());
    }

    private void checkNonCyclic1(DiagnosticPosition pos, Type t, List<TypeVar> seen) {
        final TypeVar tv;
        if  (t.hasTag(TYPEVAR) && (t.tsym.flags() & UNATTRIBUTED) != 0)
            return;
        if (seen.contains(t)) {
            tv = (TypeVar)t;
            tv.setUpperBound(types.createErrorType(t));
            log.error(pos, Errors.CyclicInheritance(t));
        } else if (t.hasTag(TYPEVAR)) {
            tv = (TypeVar)t;
            seen = seen.prepend(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
/** 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.hasTag(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.hasTag(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.isCompleted();
        if (complete) c.flags_field |= ACYCLIC;
        return complete;
    }

    
Note that we found an inheritance cycle. /** Note that we found an inheritance cycle. */
    private void noteCyclic(DiagnosticPosition pos, ClassSymbol c) {
        log.error(pos, Errors.CyclicInheritance(c));
        for (List<Type> l=types.interfaces(c.type); l.nonEmpty(); l=l.tail)
            l.head = types.createErrorType((ClassSymbol)l.head.tsym, Type.noType);
        Type st = types.supertype(c.type);
        if (st.hasTag(CLASS))
            ((ClassType)c.type).supertype_field = types.createErrorType((ClassSymbol)st.tsym, Type.noType);
        c.type = types.createErrorType(c, c.type);
        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.
/** 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, tree.sym);
    }
    //where
        
Check that all methods which implement some
 method in `ic' conform to the method they implement.
/** Check that all methods which implement some
         *  method in `ic' conform to the method they implement.
         */
        void checkImplementations(JCTree tree, ClassSymbol origin, ClassSymbol ic) {
            for (List<Type> l = types.closure(ic.type); l.nonEmpty(); l = l.tail) {
                ClassSymbol lc = (ClassSymbol)l.head.tsym;
                if ((lc.flags() & ABSTRACT) != 0) {
                    for (Symbol sym : lc.members().getSymbols(NON_RECURSIVE)) {
                        if (sym.kind == MTH &&
                            (sym.flags() & (STATIC|ABSTRACT)) == ABSTRACT) {
                            MethodSymbol absmeth = (MethodSymbol)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.
/** 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.hasTag(CLASS) &&
            (supertype.tsym.flags() & ABSTRACT) != 0)
            supertypes = supertypes.prepend(supertype);
        for (List<Type> l = supertypes; l.nonEmpty(); l = l.tail) {
            if (!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 all non-override equivalent methods accessible from 'site'
 are mutually compatible (JLS 8.4.8/9.4.1).
 @param pos  Position to be used for error reporting.
 @param site The class whose methods are checked.
 @param sym  The method symbol to be checked.
/** Check that all non-override equivalent methods accessible from 'site'
     *  are mutually compatible (JLS 8.4.8/9.4.1).
     *
     *  @param pos  Position to be used for error reporting.
     *  @param site The class whose methods are checked.
     *  @param sym  The method symbol to be checked.
     */
    void checkOverrideClashes(DiagnosticPosition pos, Type site, MethodSymbol sym) {
         ClashFilter cf = new ClashFilter(site);
        //for each method m1 that is overridden (directly or indirectly)
        //by method 'sym' in 'site'...

        List<MethodSymbol> potentiallyAmbiguousList = List.nil();
        boolean overridesAny = false;
        ArrayList<Symbol> symbolsByName = new ArrayList<>();
        types.membersClosure(site, false).getSymbolsByName(sym.name, cf).forEach(symbolsByName::add);
        for (Symbol m1 : symbolsByName) {
            if (!sym.overrides(m1, site.tsym, types, false)) {
                if (m1 == sym) {
                    continue;
                }

                if (!overridesAny) {
                    potentiallyAmbiguousList = potentiallyAmbiguousList.prepend((MethodSymbol)m1);
                }
                continue;
            }

            if (m1 != sym) {
                overridesAny = true;
                potentiallyAmbiguousList = List.nil();
            }

            //...check each method m2 that is a member of 'site'
            for (Symbol m2 : symbolsByName) {
                if (m2 == m1) continue;
                //if (i) the signature of 'sym' is not a subsignature of m1 (seen as
                //a member of 'site') and (ii) m1 has the same erasure as m2, issue an error
                if (!types.isSubSignature(sym.type, types.memberType(site, m2), Feature.STRICT_METHOD_CLASH_CHECK.allowedInSource(source)) &&
                        types.hasSameArgs(m2.erasure(types), m1.erasure(types))) {
                    sym.flags_field |= CLASH;
                    if (m1 == sym) {
                        log.error(pos, Errors.NameClashSameErasureNoOverride(
                            m1.name, types.memberType(site, m1).asMethodType().getParameterTypes(), m1.location(),
                            m2.name, types.memberType(site, m2).asMethodType().getParameterTypes(), m2.location()));
                    } else {
                        ClassType ct = (ClassType)site;
                        String kind = ct.isInterface() ? "interface" : "class";
                        log.error(pos, Errors.NameClashSameErasureNoOverride1(
                            kind,
                            ct.tsym.name,
                            m1.name,
                            types.memberType(site, m1).asMethodType().getParameterTypes(),
                            m1.location(),
                            m2.name,
                            types.memberType(site, m2).asMethodType().getParameterTypes(),
                            m2.location()));
                    }
                    return;
                }
            }
        }

        if (!overridesAny) {
            for (MethodSymbol m: potentiallyAmbiguousList) {
                checkPotentiallyAmbiguousOverloads(pos, site, sym, m);
            }
        }
    }

    
Check that all static methods accessible from 'site' are
 mutually compatible (JLS 8.4.8).
 @param pos  Position to be used for error reporting.
 @param site The class whose methods are checked.
 @param sym  The method symbol to be checked.
/** Check that all static methods accessible from 'site' are
     *  mutually compatible (JLS 8.4.8).
     *
     *  @param pos  Position to be used for error reporting.
     *  @param site The class whose methods are checked.
     *  @param sym  The method symbol to be checked.
     */
    void checkHideClashes(DiagnosticPosition pos, Type site, MethodSymbol sym) {
        ClashFilter cf = new ClashFilter(site);
        //for each method m1 that is a member of 'site'...
        for (Symbol s : types.membersClosure(site, true).getSymbolsByName(sym.name, cf)) {
            //if (i) the signature of 'sym' is not a subsignature of m1 (seen as
            //a member of 'site') and (ii) 'sym' has the same erasure as m1, issue an error
            if (!types.isSubSignature(sym.type, types.memberType(site, s), Feature.STRICT_METHOD_CLASH_CHECK.allowedInSource(source))) {
                if (types.hasSameArgs(s.erasure(types), sym.erasure(types))) {
                    log.error(pos,
                              Errors.NameClashSameErasureNoHide(sym, sym.location(), s, s.location()));
                    return;
                } else {
                    checkPotentiallyAmbiguousOverloads(pos, site, sym, (MethodSymbol)s);
                }
            }
         }
     }

     //where
     private class ClashFilter implements Filter<Symbol> {

         Type site;

         ClashFilter(Type site) {
             this.site = site;
         }

         boolean shouldSkip(Symbol s) {
             return (s.flags() & CLASH) != 0 &&
                s.owner == site.tsym;
         }

         public boolean accepts(Symbol s) {
             return s.kind == MTH &&
                     (s.flags() & SYNTHETIC) == 0 &&
                     !shouldSkip(s) &&
                     s.isInheritedIn(site.tsym, types) &&
                     !s.isConstructor();
         }
     }

    void checkDefaultMethodClashes(DiagnosticPosition pos, Type site) {
        DefaultMethodClashFilter dcf = new DefaultMethodClashFilter(site);
        for (Symbol m : types.membersClosure(site, false).getSymbols(dcf)) {
            Assert.check(m.kind == MTH);
            List<MethodSymbol> prov = types.interfaceCandidates(site, (MethodSymbol)m);
            if (prov.size() > 1) {
                ListBuffer<Symbol> abstracts = new ListBuffer<>();
                ListBuffer<Symbol> defaults = new ListBuffer<>();
                for (MethodSymbol provSym : prov) {
                    if ((provSym.flags() & DEFAULT) != 0) {
                        defaults = defaults.append(provSym);
                    } else if ((provSym.flags() & ABSTRACT) != 0) {
                        abstracts = abstracts.append(provSym);
                    }
                    if (defaults.nonEmpty() && defaults.size() + abstracts.size() >= 2) {
                        //strong semantics - issue an error if two sibling interfaces
                        //have two override-equivalent defaults - or if one is abstract
                        //and the other is default
                        Fragment diagKey;
                        Symbol s1 = defaults.first();
                        Symbol s2;
                        if (defaults.size() > 1) {
                            s2 = defaults.toList().tail.head;
                            diagKey = Fragments.IncompatibleUnrelatedDefaults(Kinds.kindName(site.tsym), site,
                                    m.name, types.memberType(site, m).getParameterTypes(),
                                    s1.location(), s2.location());

                        } else {
                            s2 = abstracts.first();
                            diagKey = Fragments.IncompatibleAbstractDefault(Kinds.kindName(site.tsym), site,
                                    m.name, types.memberType(site, m).getParameterTypes(),
                                    s1.location(), s2.location());
                        }
                        log.error(pos, Errors.TypesIncompatible(s1.location().type, s2.location().type, diagKey));
                        break;
                    }
                }
            }
        }
    }

    //where
     private class DefaultMethodClashFilter implements Filter<Symbol> {

         Type site;

         DefaultMethodClashFilter(Type site) {
             this.site = site;
         }

         public boolean accepts(Symbol s) {
             return s.kind == MTH &&
                     (s.flags() & DEFAULT) != 0 &&
                     s.isInheritedIn(site.tsym, types) &&
                     !s.isConstructor();
         }
     }

    
Report warnings for potentially ambiguous method declarations. Two declarations
are potentially ambiguous if they feature two unrelated functional interface
in same argument position (in which case, a call site passing an implicit
lambda would be ambiguous).
/**
      * Report warnings for potentially ambiguous method declarations. Two declarations
      * are potentially ambiguous if they feature two unrelated functional interface
      * in same argument position (in which case, a call site passing an implicit
      * lambda would be ambiguous).
      */
    void checkPotentiallyAmbiguousOverloads(DiagnosticPosition pos, Type site,
            MethodSymbol msym1, MethodSymbol msym2) {
        if (msym1 != msym2 &&
                Feature.DEFAULT_METHODS.allowedInSource(source) &&
                lint.isEnabled(LintCategory.OVERLOADS) &&
                (msym1.flags() & POTENTIALLY_AMBIGUOUS) == 0 &&
                (msym2.flags() & POTENTIALLY_AMBIGUOUS) == 0) {
            Type mt1 = types.memberType(site, msym1);
            Type mt2 = types.memberType(site, msym2);
            //if both generic methods, adjust type variables
            if (mt1.hasTag(FORALL) && mt2.hasTag(FORALL) &&
                    types.hasSameBounds((ForAll)mt1, (ForAll)mt2)) {
                mt2 = types.subst(mt2, ((ForAll)mt2).tvars, ((ForAll)mt1).tvars);
            }
            //expand varargs methods if needed
            int maxLength = Math.max(mt1.getParameterTypes().length(), mt2.getParameterTypes().length());
            List<Type> args1 = rs.adjustArgs(mt1.getParameterTypes(), msym1, maxLength, true);
            List<Type> args2 = rs.adjustArgs(mt2.getParameterTypes(), msym2, maxLength, true);
            //if arities don't match, exit
            if (args1.length() != args2.length()) return;
            boolean potentiallyAmbiguous = false;
            while (args1.nonEmpty() && args2.nonEmpty()) {
                Type s = args1.head;
                Type t = args2.head;
                if (!types.isSubtype(t, s) && !types.isSubtype(s, t)) {
                    if (types.isFunctionalInterface(s) && types.isFunctionalInterface(t) &&
                            types.findDescriptorType(s).getParameterTypes().length() > 0 &&
                            types.findDescriptorType(s).getParameterTypes().length() ==
                            types.findDescriptorType(t).getParameterTypes().length()) {
                        potentiallyAmbiguous = true;
                    } else {
                        break;
                    }
                }
                args1 = args1.tail;
                args2 = args2.tail;
            }
            if (potentiallyAmbiguous) {
                //we found two incompatible functional interfaces with same arity
                //this means a call site passing an implicit lambda would be ambigiuous
                msym1.flags_field |= POTENTIALLY_AMBIGUOUS;
                msym2.flags_field |= POTENTIALLY_AMBIGUOUS;
                log.warning(LintCategory.OVERLOADS, pos,
                            Warnings.PotentiallyAmbiguousOverload(msym1, msym1.location(),
                                                                  msym2, msym2.location()));
                return;
            }
        }
    }

    void checkAccessFromSerializableElement(final JCTree tree, boolean isLambda) {
        if (warnOnAnyAccessToMembers ||
            (lint.isEnabled(LintCategory.SERIAL) &&
            !lint.isSuppressed(LintCategory.SERIAL) &&
            isLambda)) {
            Symbol sym = TreeInfo.symbol(tree);
            if (!sym.kind.matches(KindSelector.VAL_MTH)) {
                return;
            }

            if (sym.kind == VAR) {
                if ((sym.flags() & PARAMETER) != 0 ||
                    sym.isLocal() ||
                    sym.name == names._this ||
                    sym.name == names._super) {
                    return;
                }
            }

            if (!types.isSubtype(sym.owner.type, syms.serializableType) &&
                isEffectivelyNonPublic(sym)) {
                if (isLambda) {
                    if (belongsToRestrictedPackage(sym)) {
                        log.warning(LintCategory.SERIAL, tree.pos(),
                                    Warnings.AccessToMemberFromSerializableLambda(sym));
                    }
                } else {
                    log.warning(tree.pos(),
                                Warnings.AccessToMemberFromSerializableElement(sym));
                }
            }
        }
    }

    private boolean isEffectivelyNonPublic(Symbol sym) {
        if (sym.packge() == syms.rootPackage) {
            return false;
        }

        while (sym.kind != PCK) {
            if ((sym.flags() & PUBLIC) == 0) {
                return true;
            }
            sym = sym.owner;
        }
        return false;
    }

    private boolean belongsToRestrictedPackage(Symbol sym) {
        String fullName = sym.packge().fullname.toString();
        return fullName.startsWith("java.") ||
                fullName.startsWith("javax.") ||
                fullName.startsWith("sun.") ||
                fullName.contains(".internal.");
    }

    
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.
/** 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.
/** 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;
                if (type.hasTag(CLASS) && !it.hasTag(CLASS)) continue; // JLS 8.1.5

                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,
                                  Errors.CantInheritDiffArg(it.tsym,
                                                            Type.toString(oldparams),
                                                            Type.toString(newparams)));
                }
                checkClassBounds(pos, seensofar, it);
            }
            Type st = types.supertype(type);
            if (type.hasTag(CLASS) && !st.hasTag(CLASS)) return; // JLS 8.1.4
            if (st != Type.noType) checkClassBounds(pos, seensofar, st);
        }

    
Enter interface into into set.
 If it existed already, issue a "repeated interface" error.
/** 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, Errors.RepeatedInterface);
        else {
            its.add(it);
        }
    }

/* *************************************************************************
 * Check annotations
 **************************************************************************/

    
Recursively validate annotations values
/**
     * Recursively validate annotations values
     */
    void validateAnnotationTree(JCTree tree) {
        class AnnotationValidator extends TreeScanner {
            @Override
            public void visitAnnotation(JCAnnotation tree) {
                if (!tree.type.isErroneous() && tree.type.tsym.isAnnotationType()) {
                    super.visitAnnotation(tree);
                    validateAnnotation(tree);
                }
            }
        }
        tree.accept(new AnnotationValidator());
    }

    

 Annotation types are restricted to primitives, String, an
 enum, an annotation, Class, Class<?>, Class<? extends
 Anything>, arrays of the preceding.
  /**
     *  {@literal
     *  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.cvarLowerBound(type).tsym == syms.classType.tsym) return;
        if (types.isArray(type) && !types.isArray(types.elemtype(type))) {
            validateAnnotationType(pos, types.elemtype(type));
            return;
        }
        log.error(pos, Errors.InvalidAnnotationMemberType);
    }

    
"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."
@jls
9.6 Annotation Types/**
     * "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."
     *
     * @jls 9.6 Annotation Types
     */
    void validateAnnotationMethod(DiagnosticPosition pos, MethodSymbol m) {
        for (Type sup = syms.annotationType; sup.hasTag(CLASS); sup = types.supertype(sup)) {
            Scope s = sup.tsym.members();
            for (Symbol sym : s.getSymbolsByName(m.name)) {
                if (sym.kind == MTH &&
                    (sym.flags() & (PUBLIC | PROTECTED)) != 0 &&
                    types.overrideEquivalent(m.type, sym.type))
                    log.error(pos, Errors.IntfAnnotationMemberClash(sym, sup));
            }
        }
    }

    
Check the annotations of a symbol.
/** Check the annotations of a symbol.
     */
    public void validateAnnotations(List<JCAnnotation> annotations, JCTree declarationTree, Symbol s) {
        for (JCAnnotation a : annotations)
            validateAnnotation(a, declarationTree, s);
    }

    
Check the type annotations.
/** Check the type annotations.
     */
    public void validateTypeAnnotations(List<JCAnnotation> annotations, boolean isTypeParameter) {
        for (JCAnnotation a : annotations)
            validateTypeAnnotation(a, isTypeParameter);
    }

    
Check an annotation of a symbol.
/** Check an annotation of a symbol.
     */
    private void validateAnnotation(JCAnnotation a, JCTree declarationTree, Symbol s) {
        validateAnnotationTree(a);
        boolean isRecordMember = (s.flags_field & RECORD) != 0 || s.enclClass() != null && s.enclClass().isRecord();

        boolean isRecordField = isRecordMember &&
                (s.flags_field & (Flags.PRIVATE | Flags.FINAL | Flags.GENERATED_MEMBER | Flags.RECORD)) != 0 &&
                declarationTree.hasTag(VARDEF) &&
                s.owner.kind == TYP;

        if (isRecordField) {
            // first we need to check if the annotation is applicable to records
            Name[] targets = getTargetNames(a);
            boolean appliesToRecords = false;
            for (Name target : targets) {
                appliesToRecords =
                                target == names.FIELD ||
                                target == names.PARAMETER ||
                                target == names.METHOD ||
                                target == names.TYPE_USE ||
                                target == names.RECORD_COMPONENT;
                if (appliesToRecords) {
                    break;
                }
            }
            if (!appliesToRecords) {
                log.error(a.pos(), Errors.AnnotationTypeNotApplicable);
            } else {
                /* lets now find the annotations in the field that are targeted to record components and append them to
                 * the corresponding record component
                 */
                ClassSymbol recordClass = (ClassSymbol) s.owner;
                RecordComponent rc = recordClass.getRecordComponent((VarSymbol)s, false);
                SymbolMetadata metadata = rc.getMetadata();
                if (metadata == null || metadata.isEmpty()) {
                    /* if not is empty then we have already been here, which is the case if multiple annotations are applied
                     * to the record component declaration
                     */
                    rc.appendAttributes(s.getRawAttributes().stream().filter(anno ->
                            Arrays.stream(getTargetNames(anno.type.tsym)).anyMatch(name -> name == names.RECORD_COMPONENT)
                    ).collect(List.collector()));
                    rc.appendUniqueTypeAttributes(s.getRawTypeAttributes());
                    // to get all the type annotations applied to the type
                    rc.type = s.type;
                }
            }
        }

        if (a.type.tsym.isAnnotationType() && !annotationApplicable(a, s)) {
            if (isRecordMember && (s.flags_field & Flags.GENERATED_MEMBER) != 0) {
                /* so we have found an annotation that is not applicable to a record member that was generated by the
                 * compiler. This was intentionally done at TypeEnter, now is the moment strip away the annotations
                 * that are not applicable to the given record member
                 */
                JCModifiers modifiers = TreeInfo.getModifiers(declarationTree);
                // lets first remove the annotation from the modifier
                if (modifiers != null) {
                    ListBuffer<JCAnnotation> newAnnotations = new ListBuffer<>();
                    for (JCAnnotation anno : modifiers.annotations) {
                        if (anno != a) {
                            newAnnotations.add(anno);
                        }
                    }
                    modifiers.annotations = newAnnotations.toList();
                }
                // now lets remove it from the symbol
                s.getMetadata().remove(a.attribute);
            } else {
                log.error(a.pos(), Errors.AnnotationTypeNotApplicable);
            }
        }

        if (a.annotationType.type.tsym == syms.functionalInterfaceType.tsym) {
            if (s.kind != TYP) {
                log.error(a.pos(), Errors.BadFunctionalIntfAnno);
            } else if (!s.isInterface() || (s.flags() & ANNOTATION) != 0) {
                log.error(a.pos(), Errors.BadFunctionalIntfAnno1(Fragments.NotAFunctionalIntf(s)));
            }
        }
    }

    public void validateTypeAnnotation(JCAnnotation a, boolean isTypeParameter) {
        Assert.checkNonNull(a.type);
        validateAnnotationTree(a);

        if (a.hasTag(TYPE_ANNOTATION) &&
                !a.annotationType.type.isErroneous() &&
                !isTypeAnnotation(a, isTypeParameter)) {
            log.error(a.pos(), Errors.AnnotationTypeNotApplicableToType(a.type));
        }
    }

    
Validate the proposed container 'repeatable' on the
annotation type symbol 's'. Report errors at position
'pos'.
Params:
s – The (annotation)type declaration annotated with a @Repeatable
repeatable – the @Repeatable on 's'
pos – where to report errors/**
     * Validate the proposed container 'repeatable' on the
     * annotation type symbol 's'. Report errors at position
     * 'pos'.
     *
     * @param s The (annotation)type declaration annotated with a @Repeatable
     * @param repeatable the @Repeatable on 's'
     * @param pos where to report errors
     */
    public void validateRepeatable(TypeSymbol s, Attribute.Compound repeatable, DiagnosticPosition pos) {
        Assert.check(types.isSameType(repeatable.type, syms.repeatableType));

        Type t = null;
        List<Pair<MethodSymbol,Attribute>> l = repeatable.values;
        if (!l.isEmpty()) {
            Assert.check(l.head.fst.name == names.value);
            t = ((Attribute.Class)l.head.snd).getValue();
        }

        if (t == null) {
            // errors should already have been reported during Annotate
            return;
        }

        validateValue(t.tsym, s, pos);
        validateRetention(t.tsym, s, pos);
        validateDocumented(t.tsym, s, pos);
        validateInherited(t.tsym, s, pos);
        validateTarget(t.tsym, s, pos);
        validateDefault(t.tsym, pos);
    }

    private void validateValue(TypeSymbol container, TypeSymbol contained, DiagnosticPosition pos) {
        Symbol sym = container.members().findFirst(names.value);
        if (sym != null && sym.kind == MTH) {
            MethodSymbol m = (MethodSymbol) sym;
            Type ret = m.getReturnType();
            if (!(ret.hasTag(ARRAY) && types.isSameType(((ArrayType)ret).elemtype, contained.type))) {
                log.error(pos,
                          Errors.InvalidRepeatableAnnotationValueReturn(container,
                                                                        ret,
                                                                        types.makeArrayType(contained.type)));
            }
        } else {
            log.error(pos, Errors.InvalidRepeatableAnnotationNoValue(container));
        }
    }

    private void validateRetention(TypeSymbol container, TypeSymbol contained, DiagnosticPosition pos) {
        Attribute.RetentionPolicy containerRetention = types.getRetention(container);
        Attribute.RetentionPolicy containedRetention = types.getRetention(contained);

        boolean error = false;
        switch (containedRetention) {
        case RUNTIME:
            if (containerRetention != Attribute.RetentionPolicy.RUNTIME) {
                error = true;
            }
            break;
        case CLASS:
            if (containerRetention == Attribute.RetentionPolicy.SOURCE)  {
                error = true;
            }
        }
        if (error ) {
            log.error(pos,
                      Errors.InvalidRepeatableAnnotationRetention(container,
                                                                  containerRetention.name(),
                                                                  contained,
                                                                  containedRetention.name()));
        }
    }

    private void validateDocumented(Symbol container, Symbol contained, DiagnosticPosition pos) {
        if (contained.attribute(syms.documentedType.tsym) != null) {
            if (container.attribute(syms.documentedType.tsym) == null) {
                log.error(pos, Errors.InvalidRepeatableAnnotationNotDocumented(container, contained));
            }
        }
    }

    private void validateInherited(Symbol container, Symbol contained, DiagnosticPosition pos) {
        if (contained.attribute(syms.inheritedType.tsym) != null) {
            if (container.attribute(syms.inheritedType.tsym) == null) {
                log.error(pos, Errors.InvalidRepeatableAnnotationNotInherited(container, contained));
            }
        }
    }

    private void validateTarget(TypeSymbol container, TypeSymbol contained, DiagnosticPosition pos) {
        // The set of targets the container is applicable to must be a subset
        // (with respect to annotation target semantics) of the set of targets
        // the contained is applicable to. The target sets may be implicit or
        // explicit.

        Set<Name> containerTargets;
        Attribute.Array containerTarget = getAttributeTargetAttribute(container);
        if (containerTarget == null) {
            containerTargets = getDefaultTargetSet();
        } else {
            containerTargets = new HashSet<>();
            for (Attribute app : containerTarget.values) {
                if (!(app instanceof Attribute.Enum)) {
                    continue; // recovery
                }
                Attribute.Enum e = (Attribute.Enum)app;
                containerTargets.add(e.value.name);
            }
        }

        Set<Name> containedTargets;
        Attribute.Array containedTarget = getAttributeTargetAttribute(contained);
        if (containedTarget == null) {
            containedTargets = getDefaultTargetSet();
        } else {
            containedTargets = new HashSet<>();
            for (Attribute app : containedTarget.values) {
                if (!(app instanceof Attribute.Enum)) {
                    continue; // recovery
                }
                Attribute.Enum e = (Attribute.Enum)app;
                containedTargets.add(e.value.name);
            }
        }

        if (!isTargetSubsetOf(containerTargets, containedTargets)) {
            log.error(pos, Errors.InvalidRepeatableAnnotationIncompatibleTarget(container, contained));
        }
    }

    /* get a set of names for the default target */
    private Set<Name> getDefaultTargetSet() {
        if (defaultTargets == null) {
            Set<Name> targets = new HashSet<>();
            targets.add(names.ANNOTATION_TYPE);
            targets.add(names.CONSTRUCTOR);
            targets.add(names.FIELD);
            targets.add(names.RECORD_COMPONENT);
            targets.add(names.LOCAL_VARIABLE);
            targets.add(names.METHOD);
            targets.add(names.PACKAGE);
            targets.add(names.PARAMETER);
            targets.add(names.TYPE);

            defaultTargets = java.util.Collections.unmodifiableSet(targets);
        }

        return defaultTargets;
    }
    private Set<Name> defaultTargets;


    
Checks that s is a subset of t, with respect to ElementType
semantics, specifically {ANNOTATION_TYPE} is a subset of {TYPE},
and {TYPE_USE} covers the set {ANNOTATION_TYPE, TYPE, TYPE_USE,
TYPE_PARAMETER}.
/** Checks that s is a subset of t, with respect to ElementType
     * semantics, specifically {ANNOTATION_TYPE} is a subset of {TYPE},
     * and {TYPE_USE} covers the set {ANNOTATION_TYPE, TYPE, TYPE_USE,
     * TYPE_PARAMETER}.
     */
    private boolean isTargetSubsetOf(Set<Name> s, Set<Name> t) {
        // Check that all elements in s are present in t
        for (Name n2 : s) {
            boolean currentElementOk = false;
            for (Name n1 : t) {
                if (n1 == n2) {
                    currentElementOk = true;
                    break;
                } else if (n1 == names.TYPE && n2 == names.ANNOTATION_TYPE) {
                    currentElementOk = true;
                    break;
                } else if (n1 == names.TYPE_USE &&
                        (n2 == names.TYPE ||
                         n2 == names.ANNOTATION_TYPE ||
                         n2 == names.TYPE_PARAMETER)) {
                    currentElementOk = true;
                    break;
                }
            }
            if (!currentElementOk)
                return false;
        }
        return true;
    }

    private void validateDefault(Symbol container, DiagnosticPosition pos) {
        // validate that all other elements of containing type has defaults
        Scope scope = container.members();
        for(Symbol elm : scope.getSymbols()) {
            if (elm.name != names.value &&
                elm.kind == MTH &&
                ((MethodSymbol)elm).defaultValue == null) {
                log.error(pos,
                          Errors.InvalidRepeatableAnnotationElemNondefault(container, elm));
            }
        }
    }

    
Is s a method symbol that overrides a method in a 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 (Symbol sym : scope.getSymbolsByName(m.name)) {
                if (!sym.isStatic() && m.overrides(sym, owner, types, true))
                    return true;
            }
        }
        return false;
    }

    
Is the annotation applicable to types? /** Is the annotation applicable to types? */
    protected boolean isTypeAnnotation(JCAnnotation a, boolean isTypeParameter) {
        List<Attribute> targets = typeAnnotations.annotationTargets(a.annotationType.type.tsym);
        return (targets == null) ?
                false :
                targets.stream()
                        .anyMatch(attr -> isTypeAnnotation(attr, isTypeParameter));
    }
    //where
        boolean isTypeAnnotation(Attribute a, boolean isTypeParameter) {
            Attribute.Enum e = (Attribute.Enum)a;
            return (e.value.name == names.TYPE_USE ||
                    (isTypeParameter && e.value.name == names.TYPE_PARAMETER));
        }

    
Is the annotation applicable to the symbol? /** Is the annotation applicable to the symbol? */
    Name[] getTargetNames(JCAnnotation a) {
        return getTargetNames(a.annotationType.type.tsym);
    }

    public Name[] getTargetNames(TypeSymbol annoSym) {
        Attribute.Array arr = getAttributeTargetAttribute(annoSym);
        Name[] targets;
        if (arr == null) {
            targets = defaultTargetMetaInfo();
        } else {
            // TODO: can we optimize this?
            targets = new Name[arr.values.length];
            for (int i=0; i<arr.values.length; ++i) {
                Attribute app = arr.values[i];
                if (!(app instanceof Attribute.Enum)) {
                    return new Name[0];
                }
                Attribute.Enum e = (Attribute.Enum) app;
                targets[i] = e.value.name;
            }
        }
        return targets;
    }

    @SuppressWarnings("preview")
    boolean annotationApplicable(JCAnnotation a, Symbol s) {
        Attribute.Array arr = getAttributeTargetAttribute(a.annotationType.type.tsym);
        Name[] targets;

        if (arr == null) {
            targets = defaultTargetMetaInfo();
        } else {
            // TODO: can we optimize this?
            targets = new Name[arr.values.length];
            for (int i=0; i<arr.values.length; ++i) {
                Attribute app = arr.values[i];
                if (!(app instanceof Attribute.Enum)) {
                    return true; // recovery
                }
                Attribute.Enum e = (Attribute.Enum) app;
                targets[i] = e.value.name;
            }
        }
        for (Name target : targets) {
            if (target == names.TYPE) {
                if (s.kind == TYP)
                    return true;
            } else if (target == names.FIELD) {
                if (s.kind == VAR && s.owner.kind != MTH)
                    return true;
            } else if (target == names.RECORD_COMPONENT) {
                if (s.getKind() == ElementKind.RECORD_COMPONENT) {
                    return true;
                }
            } else if (target == names.METHOD) {
                if (s.kind == MTH && !s.isConstructor())
                    return true;
            } else if (target == names.PARAMETER) {
                if (s.kind == VAR &&
                    (s.owner.kind == MTH && (s.flags() & PARAMETER) != 0)) {
                    return true;
                }
            } else if (target == names.CONSTRUCTOR) {
                if (s.kind == MTH && s.isConstructor())
                    return true;
            } else if (target == names.LOCAL_VARIABLE) {
                if (s.kind == VAR && s.owner.kind == MTH &&
                      (s.flags() & PARAMETER) == 0) {
                    return true;
                }
            } else if (target == names.ANNOTATION_TYPE) {
                if (s.kind == TYP && (s.flags() & ANNOTATION) != 0) {
                    return true;
                }
            } else if (target == names.PACKAGE) {
                if (s.kind == PCK)
                    return true;
            } else if (target == names.TYPE_USE) {
                if (s.kind == VAR && s.owner.kind == MTH && s.type.hasTag(NONE)) {
                    //cannot type annotate implictly typed locals
                    return false;
                } else if (s.kind == TYP || s.kind == VAR ||
                        (s.kind == MTH && !s.isConstructor() &&
                                !s.type.getReturnType().hasTag(VOID)) ||
                        (s.kind == MTH && s.isConstructor())) {
                    return true;
                }
            } else if (target == names.TYPE_PARAMETER) {
                if (s.kind == TYP && s.type.hasTag(TYPEVAR))
                    return true;
            } else
                return true; // Unknown ElementType. This should be an error at declaration site,
                             // assume applicable.
        }
        return false;
    }

    Attribute.Array getAttributeTargetAttribute(TypeSymbol s) {
        Attribute.Compound atTarget = s.getAnnotationTypeMetadata().getTarget();
        if (atTarget == null) return null; // ok, is applicable
        Attribute atValue = atTarget.member(names.value);
        if (!(atValue instanceof Attribute.Array)) return null; // error recovery
        return (Attribute.Array) atValue;
    }

    public final Name[] dfltTargetMeta;
    private Name[] defaultTargetMetaInfo() {
        return dfltTargetMeta;
    }

    
Check an annotation value.
Params:
a – The annotation tree to check
Returns:
true if this annotation tree is valid, otherwise false/** Check an annotation value.
     *
     * @param a The annotation tree to check
     * @return true if this annotation tree is valid, otherwise false
     */
    public boolean validateAnnotationDeferErrors(JCAnnotation a) {
        boolean res = false;
        final Log.DiagnosticHandler diagHandler = new Log.DiscardDiagnosticHandler(log);
        try {
            res = validateAnnotation(a);
        } finally {
            log.popDiagnosticHandler(diagHandler);
        }
        return res;
    }

    private boolean validateAnnotation(JCAnnotation a) {
        boolean isValid = true;
        AnnotationTypeMetadata metadata = a.annotationType.type.tsym.getAnnotationTypeMetadata();

        // collect an inventory of the annotation elements
        Set<MethodSymbol> elements = metadata.getAnnotationElements();

        // remove the ones that are assigned values
        for (JCTree arg : a.args) {
            if (!arg.hasTag(ASSIGN)) continue; // recovery
            JCAssign assign = (JCAssign)arg;
            Symbol m = TreeInfo.symbol(assign.lhs);
            if (m == null || m.type.isErroneous()) continue;
            if (!elements.remove(m)) {
                isValid = false;
                log.error(assign.lhs.pos(),
                          Errors.DuplicateAnnotationMemberValue(m.name, a.type));
            }
        }

        // all the remaining ones better have default values
        List<Name> missingDefaults = List.nil();
        Set<MethodSymbol> membersWithDefault = metadata.getAnnotationElementsWithDefault();
        for (MethodSymbol m : elements) {
            if (m.type.isErroneous())
                continue;

            if (!membersWithDefault.contains(m))
                missingDefaults = missingDefaults.append(m.name);
        }
        missingDefaults = missingDefaults.reverse();
        if (missingDefaults.nonEmpty()) {
            isValid = false;
            Error errorKey = (missingDefaults.size() > 1)
                    ? Errors.AnnotationMissingDefaultValue1(a.type, missingDefaults)
                    : Errors.AnnotationMissingDefaultValue(a.type, missingDefaults);
            log.error(a.pos(), errorKey);
        }

        return isValid && validateTargetAnnotationValue(a);
    }

    /* Validate the special java.lang.annotation.Target annotation */
    boolean validateTargetAnnotationValue(JCAnnotation a) {
        // 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 true;

        boolean isValid = true;
        if (!a.args.head.hasTag(ASSIGN)) return false; // error recovery
        JCAssign assign = (JCAssign) a.args.head;
        Symbol m = TreeInfo.symbol(assign.lhs);
        if (m.name != names.value) return false;
        JCTree rhs = assign.rhs;
        if (!rhs.hasTag(NEWARRAY)) return false;
        JCNewArray na = (JCNewArray) rhs;
        Set<Symbol> targets = new HashSet<>();
        for (JCTree elem : na.elems) {
            if (!targets.add(TreeInfo.symbol(elem))) {
                isValid = false;
                log.error(elem.pos(), Errors.RepeatedAnnotationTarget);
            }
        }
        return isValid;
    }

    void checkDeprecatedAnnotation(DiagnosticPosition pos, Symbol s) {
        if (lint.isEnabled(LintCategory.DEP_ANN) && s.isDeprecatableViaAnnotation() &&
            (s.flags() & DEPRECATED) != 0 &&
            !syms.deprecatedType.isErroneous() &&
            s.attribute(syms.deprecatedType.tsym) == null) {
            log.warning(LintCategory.DEP_ANN,
                    pos, Warnings.MissingDeprecatedAnnotation);
        }
        // Note: @Deprecated has no effect on local variables, parameters and package decls.
        if (lint.isEnabled(LintCategory.DEPRECATION) && !s.isDeprecatableViaAnnotation()) {
            if (!syms.deprecatedType.isErroneous() && s.attribute(syms.deprecatedType.tsym) != null) {
                log.warning(LintCategory.DEPRECATION, pos,
                            Warnings.DeprecatedAnnotationHasNoEffect(Kinds.kindName(s)));
            }
        }
    }

    void checkDeprecated(final DiagnosticPosition pos, final Symbol other, final Symbol s) {
        checkDeprecated(() -> pos, other, s);
    }

    void checkDeprecated(Supplier<DiagnosticPosition> pos, final Symbol other, final Symbol s) {
        if ( (s.isDeprecatedForRemoval()
                || s.isDeprecated() && !other.isDeprecated())
                && (s.outermostClass() != other.outermostClass() || s.outermostClass() == null)) {
            deferredLintHandler.report(() -> warnDeprecated(pos.get(), s));
        }
    }

    void checkSunAPI(final DiagnosticPosition pos, final Symbol s) {
        if ((s.flags() & PROPRIETARY) != 0) {
            deferredLintHandler.report(() -> {
                log.mandatoryWarning(pos, Warnings.SunProprietary(s));
            });
        }
    }

    void checkProfile(final DiagnosticPosition pos, final Symbol s) {
        if (profile != Profile.DEFAULT && (s.flags() & NOT_IN_PROFILE) != 0) {
            log.error(pos, Errors.NotInProfile(s, profile));
        }
    }

    void checkPreview(DiagnosticPosition pos, Symbol s) {
        if ((s.flags() & PREVIEW_API) != 0) {
            if ((s.flags() & PREVIEW_ESSENTIAL_API) != 0 && !preview.isEnabled()) {
                log.error(pos, Errors.IsPreview(s));
            } else {
                deferredLintHandler.report(() -> warnPreview(pos, s));
            }
        }
    }

/* *************************************************************************
 * Check for recursive annotation elements.
 **************************************************************************/

    
Check for cycles in the graph of annotation elements.
/** Check for cycles in the graph of annotation elements.
     */
    void checkNonCyclicElements(JCClassDecl tree) {
        if ((tree.sym.flags_field & ANNOTATION) == 0) return;
        Assert.check((tree.sym.flags_field & LOCKED) == 0);
        try {
            tree.sym.flags_field |= LOCKED;
            for (JCTree def : tree.defs) {
                if (!def.hasTag(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, Errors.CyclicAnnotationElement(tsym));
            return;
        }
        try {
            tsym.flags_field |= LOCKED;
            for (Symbol s : tsym.members().getSymbols(NON_RECURSIVE)) {
                if (s.kind != 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.getTag()) {
        case CLASS:
            if ((type.tsym.flags() & ANNOTATION) != 0)
                checkNonCyclicElementsInternal(pos, type.tsym);
            break;
        case 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.
/** Check for cycles in the graph of constructors calling other
     *  constructors.
     */
    void checkCyclicConstructors(JCClassDecl tree) {
        Map<Symbol,Symbol> callMap = new HashMap<>();

        // 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.
/** 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),
                          Errors.RecursiveCtorInvocation);
            } else {
                ctor.flags_field |= LOCKED;
                checkCyclicConstructor(tree, callMap.remove(ctor), callMap);
                ctor.flags_field &= ~LOCKED;
            }
            ctor.flags_field |= ACYCLIC;
        }
    }

/* *************************************************************************
 * Miscellaneous
 **************************************************************************/

    
 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
/**
     *  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(final DiagnosticPosition pos, Symbol operator, Type operand) {
        if (operand.constValue() != null
            && operand.getTag().isSubRangeOf(LONG)
            && ((Number) (operand.constValue())).longValue() == 0) {
            int opc = ((OperatorSymbol)operator).opcode;
            if (opc == ByteCodes.idiv || opc == ByteCodes.imod
                || opc == ByteCodes.ldiv || opc == ByteCodes.lmod) {
                deferredLintHandler.report(() -> warnDivZero(pos));
            }
        }
    }

    
Check for empty statements after if
/**
     * Check for empty statements after if
     */
    void checkEmptyIf(JCIf tree) {
        if (tree.thenpart.hasTag(SKIP) && tree.elsepart == null &&
                lint.isEnabled(LintCategory.EMPTY))
            log.warning(LintCategory.EMPTY, tree.thenpart.pos(), Warnings.EmptyIf);
    }

    
Check that symbol is unique in given scope.
 @param pos           Position for error reporting.
 @param sym           The symbol.
 @param s             The scope.
/** 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 (Symbol byName : s.getSymbolsByName(sym.name, NON_RECURSIVE)) {
            if (sym != byName &&
                    (byName.flags() & CLASH) == 0 &&
                    sym.kind == byName.kind &&
                    sym.name != names.error &&
                    (sym.kind != MTH ||
                     types.hasSameArgs(sym.type, byName.type) ||
                     types.hasSameArgs(types.erasure(sym.type), types.erasure(byName.type)))) {
                if ((sym.flags() & VARARGS) != (byName.flags() & VARARGS)) {
                    sym.flags_field |= CLASH;
                    varargsDuplicateError(pos, sym, byName);
                    return true;
                } else if (sym.kind == MTH && !types.hasSameArgs(sym.type, byName.type, false)) {
                    duplicateErasureError(pos, sym, byName);
                    sym.flags_field |= CLASH;
                    return true;
                } else if ((sym.flags() & MATCH_BINDING) != 0 &&
                           (byName.flags() & MATCH_BINDING) != 0 &&
                           (byName.flags() & MATCH_BINDING_TO_OUTER) == 0) {
                    if (!sym.type.isErroneous()) {
                        log.error(pos, Errors.MatchBindingExists);
                        sym.flags_field |= CLASH;
                    }
                    return false;
                } else {
                    duplicateError(pos, byName);
                    return false;
                }
            }
        }
        return true;
    }

    
Report duplicate declaration error.
/** Report duplicate declaration error.
     */
    void duplicateErasureError(DiagnosticPosition pos, Symbol sym1, Symbol sym2) {
        if (!sym1.type.isErroneous() && !sym2.type.isErroneous()) {
            log.error(pos, Errors.NameClashSameErasure(sym1, sym2));
        }
    }

    
Check that types imported through the ordinary imports don't clash with types imported
by other (static or ordinary) imports. Note that two static imports may import two clashing
types without an error on the imports.
Params:
toplevel –       The toplevel tree for which the test should be performed./**Check that types imported through the ordinary imports don't clash with types imported
     * by other (static or ordinary) imports. Note that two static imports may import two clashing
     * types without an error on the imports.
     * @param toplevel       The toplevel tree for which the test should be performed.
     */
    void checkImportsUnique(JCCompilationUnit toplevel) {
        WriteableScope ordinallyImportedSoFar = WriteableScope.create(toplevel.packge);
        WriteableScope staticallyImportedSoFar = WriteableScope.create(toplevel.packge);
        WriteableScope topLevelScope = toplevel.toplevelScope;

        for (JCTree def : toplevel.defs) {
            if (!def.hasTag(IMPORT))
                continue;

            JCImport imp = (JCImport) def;

            if (imp.importScope == null)
                continue;

            for (Symbol sym : imp.importScope.getSymbols(sym -> sym.kind == TYP)) {
                if (imp.isStatic()) {
                    checkUniqueImport(imp.pos(), ordinallyImportedSoFar, staticallyImportedSoFar, topLevelScope, sym, true);
                    staticallyImportedSoFar.enter(sym);
                } else {
                    checkUniqueImport(imp.pos(), ordinallyImportedSoFar, staticallyImportedSoFar, topLevelScope, sym, false);
                    ordinallyImportedSoFar.enter(sym);
                }
            }

            imp.importScope = null;
        }
    }

    
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 ordinallyImportedSoFar  A Scope containing types imported so far through
                                ordinary imports.
 @param staticallyImportedSoFar A Scope containing types imported so far through
                                static imports.
 @param topLevelScope           The current file's top-level Scope
 @param sym                     The symbol.
 @param staticImport            Whether or not this was a static import
/** 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 ordinallyImportedSoFar  A Scope containing types imported so far through
     *                                 ordinary imports.
     *  @param staticallyImportedSoFar A Scope containing types imported so far through
     *                                 static imports.
     *  @param topLevelScope           The current file's top-level Scope
     *  @param sym                     The symbol.
     *  @param staticImport            Whether or not this was a static import
     */
    private boolean checkUniqueImport(DiagnosticPosition pos, Scope ordinallyImportedSoFar,
                                      Scope staticallyImportedSoFar, Scope topLevelScope,
                                      Symbol sym, boolean staticImport) {
        Filter<Symbol> duplicates = candidate -> candidate != sym && !candidate.type.isErroneous();
        Symbol ordinaryClashing = ordinallyImportedSoFar.findFirst(sym.name, duplicates);
        Symbol staticClashing = null;
        if (ordinaryClashing == null && !staticImport) {
            staticClashing = staticallyImportedSoFar.findFirst(sym.name, duplicates);
        }
        if (ordinaryClashing != null || staticClashing != null) {
            if (ordinaryClashing != null)
                log.error(pos, Errors.AlreadyDefinedSingleImport(ordinaryClashing));
            else
                log.error(pos, Errors.AlreadyDefinedStaticSingleImport(staticClashing));
            return false;
        }
        Symbol clashing = topLevelScope.findFirst(sym.name, duplicates);
        if (clashing != null) {
            log.error(pos, Errors.AlreadyDefinedThisUnit(clashing));
            return false;
        }
        return true;
    }

    
Check that a qualified name is in canonical form (for import decls).
/** Check that a qualified name is in canonical form (for import decls).
     */
    public void checkCanonical(JCTree tree) {
        if (!isCanonical(tree))
            log.error(tree.pos(),
                      Errors.ImportRequiresCanonical(TreeInfo.symbol(tree)));
    }
        // where
        private boolean isCanonical(JCTree tree) {
            while (tree.hasTag(SELECT)) {
                JCFieldAccess s = (JCFieldAccess) tree;
                if (s.sym.owner.getQualifiedName() != TreeInfo.symbol(s.selected).getQualifiedName())
                    return false;
                tree = s.selected;
            }
            return true;
        }

    
Check that an auxiliary class is not accessed from any other file than its own.
/** Check that an auxiliary class is not accessed from any other file than its own.
     */
    void checkForBadAuxiliaryClassAccess(DiagnosticPosition pos, Env<AttrContext> env, ClassSymbol c) {
        if (lint.isEnabled(Lint.LintCategory.AUXILIARYCLASS) &&
            (c.flags() & AUXILIARY) != 0 &&
            rs.isAccessible(env, c) &&
            !fileManager.isSameFile(c.sourcefile, env.toplevel.sourcefile))
        {
            log.warning(pos,
                        Warnings.AuxiliaryClassAccessedFromOutsideOfItsSourceFile(c, c.sourcefile));
        }
    }

    private class ConversionWarner extends Warner {
        final String uncheckedKey;
        final Type found;
        final Type expected;
        public ConversionWarner(DiagnosticPosition pos, String uncheckedKey, Type found, Type expected) {
            super(pos);
            this.uncheckedKey = uncheckedKey;
            this.found = found;
            this.expected = expected;
        }

        @Override
        public void warn(LintCategory lint) {
            boolean warned = this.warned;
            super.warn(lint);
            if (warned) return; // suppress redundant diagnostics
            switch (lint) {
                case UNCHECKED:
                    Check.this.warnUnchecked(pos(), Warnings.ProbFoundReq(diags.fragment(uncheckedKey), found, expected));
                    break;
                case VARARGS:
                    if (method != null &&
                            method.attribute(syms.trustMeType.tsym) != null &&
                            isTrustMeAllowedOnMethod(method) &&
                            !types.isReifiable(method.type.getParameterTypes().last())) {
                        Check.this.warnUnsafeVararg(pos(), Warnings.VarargsUnsafeUseVarargsParam(method.params.last()));
                    }
                    break;
                default:
                    throw new AssertionError("Unexpected lint: " + lint);
            }
        }
    }

    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);
    }

    public void checkFunctionalInterface(JCClassDecl tree, ClassSymbol cs) {
        Compound functionalType = cs.attribute(syms.functionalInterfaceType.tsym);

        if (functionalType != null) {
            try {
                types.findDescriptorSymbol((TypeSymbol)cs);
            } catch (Types.FunctionDescriptorLookupError ex) {
                DiagnosticPosition pos = tree.pos();
                for (JCAnnotation a : tree.getModifiers().annotations) {
                    if (a.annotationType.type.tsym == syms.functionalInterfaceType.tsym) {
                        pos = a.pos();
                        break;
                    }
                }
                log.error(pos, Errors.BadFunctionalIntfAnno1(ex.getDiagnostic()));
            }
        }
    }

    public void checkImportsResolvable(final JCCompilationUnit toplevel) {
        for (final JCImport imp : toplevel.getImports()) {
            if (!imp.staticImport || !imp.qualid.hasTag(SELECT))
                continue;
            final JCFieldAccess select = (JCFieldAccess) imp.qualid;
            final Symbol origin;
            if (select.name == names.asterisk || (origin = TreeInfo.symbol(select.selected)) == null || origin.kind != TYP)
                continue;

            TypeSymbol site = (TypeSymbol) TreeInfo.symbol(select.selected);
            if (!checkTypeContainsImportableElement(site, site, toplevel.packge, select.name, new HashSet<Symbol>())) {
                log.error(imp.pos(),
                          Errors.CantResolveLocation(KindName.STATIC,
                                                     select.name,
                                                     null,
                                                     null,
                                                     Fragments.Location(kindName(site),
                                                                        site,
                                                                        null)));
            }
        }
    }

    // Check that packages imported are in scope (JLS 7.4.3, 6.3, 6.5.3.1, 6.5.3.2)
    public void checkImportedPackagesObservable(final JCCompilationUnit toplevel) {
        OUTER: for (JCImport imp : toplevel.getImports()) {
            if (!imp.staticImport && TreeInfo.name(imp.qualid) == names.asterisk) {
                TypeSymbol tsym = ((JCFieldAccess)imp.qualid).selected.type.tsym;
                if (tsym.kind == PCK && tsym.members().isEmpty() &&
                    !(Feature.IMPORT_ON_DEMAND_OBSERVABLE_PACKAGES.allowedInSource(source) && tsym.exists())) {
                    log.error(DiagnosticFlag.RESOLVE_ERROR, imp.pos, Errors.DoesntExist(tsym));
                }
            }
        }
    }

    private boolean checkTypeContainsImportableElement(TypeSymbol tsym, TypeSymbol origin, PackageSymbol packge, Name name, Set<Symbol> processed) {
        if (tsym == null || !processed.add(tsym))
            return false;

            // also search through inherited names
        if (checkTypeContainsImportableElement(types.supertype(tsym.type).tsym, origin, packge, name, processed))
            return true;

        for (Type t : types.interfaces(tsym.type))
            if (checkTypeContainsImportableElement(t.tsym, origin, packge, name, processed))
                return true;

        for (Symbol sym : tsym.members().getSymbolsByName(name)) {
            if (sym.isStatic() &&
                importAccessible(sym, packge) &&
                sym.isMemberOf(origin, types)) {
                return true;
            }
        }

        return false;
    }

    // is the sym accessible everywhere in packge?
    public boolean importAccessible(Symbol sym, PackageSymbol packge) {
        try {
            int flags = (int)(sym.flags() & AccessFlags);
            switch (flags) {
            default:
            case PUBLIC:
                return true;
            case PRIVATE:
                return false;
            case 0:
            case PROTECTED:
                return sym.packge() == packge;
            }
        } catch (ClassFinder.BadClassFile err) {
            throw err;
        } catch (CompletionFailure ex) {
            return false;
        }
    }

    public void checkLeaksNotAccessible(Env<AttrContext> env, JCClassDecl check) {
        JCCompilationUnit toplevel = env.toplevel;

        if (   toplevel.modle == syms.unnamedModule
            || toplevel.modle == syms.noModule
            || (check.sym.flags() & COMPOUND) != 0) {
            return ;
        }

        ExportsDirective currentExport = findExport(toplevel.packge);

        if (   currentExport == null //not exported
            || currentExport.modules != null) //don't check classes in qualified export
            return ;

        new TreeScanner() {
            Lint lint = env.info.lint;
            boolean inSuperType;

            @Override
            public void visitBlock(JCBlock tree) {
            }
            @Override
            public void visitMethodDef(JCMethodDecl tree) {
                if (!isAPISymbol(tree.sym))
                    return;
                Lint prevLint = lint;
                try {
                    lint = lint.augment(tree.sym);
                    if (lint.isEnabled(LintCategory.EXPORTS)) {
                        super.visitMethodDef(tree);
                    }
                } finally {
                    lint = prevLint;
                }
            }
            @Override
            public void visitVarDef(JCVariableDecl tree) {
                if (!isAPISymbol(tree.sym) && tree.sym.owner.kind != MTH)
                    return;
                Lint prevLint = lint;
                try {
                    lint = lint.augment(tree.sym);
                    if (lint.isEnabled(LintCategory.EXPORTS)) {
                        scan(tree.mods);
                        scan(tree.vartype);
                    }
                } finally {
                    lint = prevLint;
                }
            }
            @Override
            public void visitClassDef(JCClassDecl tree) {
                if (tree != check)
                    return ;

                if (!isAPISymbol(tree.sym))
                    return ;

                Lint prevLint = lint;
                try {
                    lint = lint.augment(tree.sym);
                    if (lint.isEnabled(LintCategory.EXPORTS)) {
                        scan(tree.mods);
                        scan(tree.typarams);
                        try {
                            inSuperType = true;
                            scan(tree.extending);
                            scan(tree.implementing);
                        } finally {
                            inSuperType = false;
                        }
                        scan(tree.defs);
                    }
                } finally {
                    lint = prevLint;
                }
            }
            @Override
            public void visitTypeApply(JCTypeApply tree) {
                scan(tree.clazz);
                boolean oldInSuperType = inSuperType;
                try {
                    inSuperType = false;
                    scan(tree.arguments);
                } finally {
                    inSuperType = oldInSuperType;
                }
            }
            @Override
            public void visitIdent(JCIdent tree) {
                Symbol sym = TreeInfo.symbol(tree);
                if (sym.kind == TYP && !sym.type.hasTag(TYPEVAR)) {
                    checkVisible(tree.pos(), sym, toplevel.packge, inSuperType);
                }
            }

            @Override
            public void visitSelect(JCFieldAccess tree) {
                Symbol sym = TreeInfo.symbol(tree);
                Symbol sitesym = TreeInfo.symbol(tree.selected);
                if (sym.kind == TYP && sitesym.kind == PCK) {
                    checkVisible(tree.pos(), sym, toplevel.packge, inSuperType);
                } else {
                    super.visitSelect(tree);
                }
            }

            @Override
            public void visitAnnotation(JCAnnotation tree) {
                if (tree.attribute.type.tsym.getAnnotation(java.lang.annotation.Documented.class) != null)
                    super.visitAnnotation(tree);
            }

        }.scan(check);
    }
        //where:
        private ExportsDirective findExport(PackageSymbol pack) {
            for (ExportsDirective d : pack.modle.exports) {
                if (d.packge == pack)
                    return d;
            }

            return null;
        }
        private boolean isAPISymbol(Symbol sym) {
            while (sym.kind != PCK) {
                if ((sym.flags() & Flags.PUBLIC) == 0 && (sym.flags() & Flags.PROTECTED) == 0) {
                    return false;
                }
                sym = sym.owner;
            }
            return true;
        }
        private void checkVisible(DiagnosticPosition pos, Symbol what, PackageSymbol inPackage, boolean inSuperType) {
            if (!isAPISymbol(what) && !inSuperType) { //package private/private element
                log.warning(LintCategory.EXPORTS, pos, Warnings.LeaksNotAccessible(kindName(what), what, what.packge().modle));
                return ;
            }

            PackageSymbol whatPackage = what.packge();
            ExportsDirective whatExport = findExport(whatPackage);
            ExportsDirective inExport = findExport(inPackage);

            if (whatExport == null) { //package not exported:
                log.warning(LintCategory.EXPORTS, pos, Warnings.LeaksNotAccessibleUnexported(kindName(what), what, what.packge().modle));
                return ;
            }

            if (whatExport.modules != null) {
                if (inExport.modules == null || !whatExport.modules.containsAll(inExport.modules)) {
                    log.warning(LintCategory.EXPORTS, pos, Warnings.LeaksNotAccessibleUnexportedQualified(kindName(what), what, what.packge().modle));
                }
            }

            if (whatPackage.modle != inPackage.modle && whatPackage.modle != syms.java_base) {
                //check that relativeTo.modle requires transitive what.modle, somehow:
                List<ModuleSymbol> todo = List.of(inPackage.modle);

                while (todo.nonEmpty()) {
                    ModuleSymbol current = todo.head;
                    todo = todo.tail;
                    if (current == whatPackage.modle)
                        return ; //OK
                    if ((current.flags() & Flags.AUTOMATIC_MODULE) != 0)
                        continue; //for automatic modules, don't look into their dependencies
                    for (RequiresDirective req : current.requires) {
                        if (req.isTransitive()) {
                            todo = todo.prepend(req.module);
                        }
                    }
                }

                log.warning(LintCategory.EXPORTS, pos, Warnings.LeaksNotAccessibleNotRequiredTransitive(kindName(what), what, what.packge().modle));
            }
        }

    void checkModuleExists(final DiagnosticPosition pos, ModuleSymbol msym) {
        if (msym.kind != MDL) {
            deferredLintHandler.report(() -> {
                if (lint.isEnabled(LintCategory.MODULE))
                    log.warning(LintCategory.MODULE, pos, Warnings.ModuleNotFound(msym));
            });
        }
    }

    void checkPackageExistsForOpens(final DiagnosticPosition pos, PackageSymbol packge) {
        if (packge.members().isEmpty() &&
            ((packge.flags() & Flags.HAS_RESOURCE) == 0)) {
            deferredLintHandler.report(() -> {
                if (lint.isEnabled(LintCategory.OPENS))
                    log.warning(pos, Warnings.PackageEmptyOrNotFound(packge));
            });
        }
    }

    void checkModuleRequires(final DiagnosticPosition pos, final RequiresDirective rd) {
        if ((rd.module.flags() & Flags.AUTOMATIC_MODULE) != 0) {
            deferredLintHandler.report(() -> {
                if (rd.isTransitive() && lint.isEnabled(LintCategory.REQUIRES_TRANSITIVE_AUTOMATIC)) {
                    log.warning(pos, Warnings.RequiresTransitiveAutomatic);
                } else if (lint.isEnabled(LintCategory.REQUIRES_AUTOMATIC)) {
                    log.warning(pos, Warnings.RequiresAutomatic);
                }
            });
        }
    }

}