/*
 * Copyright (c) 1999, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javac.jvm;

import java.io.*;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import java.util.LinkedHashSet;
import java.util.function.ToIntFunction;

import javax.tools.JavaFileManager;
import javax.tools.FileObject;
import javax.tools.JavaFileManager.Location;
import javax.tools.JavaFileObject;

import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Attribute.RetentionPolicy;
import com.sun.tools.javac.code.Directive.*;
import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.code.Type.*;
import com.sun.tools.javac.code.Types.SignatureGenerator.InvalidSignatureException;
import com.sun.tools.javac.comp.Check;
import com.sun.tools.javac.file.PathFileObject;
import com.sun.tools.javac.jvm.PoolConstant.LoadableConstant;
import com.sun.tools.javac.jvm.PoolConstant.Dynamic.BsmKey;
import com.sun.tools.javac.resources.CompilerProperties.Errors;
import com.sun.tools.javac.resources.CompilerProperties.Fragments;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.List;

import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Kinds.Kind.*;
import static com.sun.tools.javac.code.Scope.LookupKind.NON_RECURSIVE;
import static com.sun.tools.javac.code.TypeTag.*;
import static com.sun.tools.javac.main.Option.*;

import static javax.tools.StandardLocation.CLASS_OUTPUT;

This class provides operations to map an internal symbol table graph
 rooted in a ClassSymbol into a classfile.
 
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.
/** This class provides operations to map an internal symbol table graph
 *  rooted in a ClassSymbol into a classfile.
 *
 *  <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 ClassWriter extends ClassFile {
    protected static final Context.Key<ClassWriter> classWriterKey = new Context.Key<>();

    private final Options options;

    
Switch: verbose output.
/** Switch: verbose output.
     */
    private boolean verbose;

    
Switch: emit source file attribute.
/** Switch: emit source file attribute.
     */
    private boolean emitSourceFile;

    
Switch: generate CharacterRangeTable attribute.
/** Switch: generate CharacterRangeTable attribute.
     */
    private boolean genCrt;

    
Switch: describe the generated stackmap.
/** Switch: describe the generated stackmap.
     */
    private boolean debugstackmap;

    
Preview language level.
/** Preview language level.
     */
    private Preview preview;

    
Target class version.
/**
     * Target class version.
     */
    private Target target;

    
Source language version.
/**
     * Source language version.
     */
    private Source source;

    
Type utilities. /** Type utilities. */
    private Types types;

    private Check check;

    
If true, class files will be written in module-specific subdirectories
of the CLASS_OUTPUT location.
/**
     * If true, class files will be written in module-specific subdirectories
     * of the CLASS_OUTPUT location.
     */
    public boolean multiModuleMode;

    private List<ToIntFunction<Symbol>> extraAttributeHooks = List.nil();

    
The initial sizes of the data and constant pool buffers.
 Sizes are increased when buffers get full.
/** The initial sizes of the data and constant pool buffers.
     *  Sizes are increased when buffers get full.
     */
    static final int DATA_BUF_SIZE = 0x0fff0;
    static final int CLASS_BUF_SIZE = 0x1fff0;

    
An output buffer for member info.
/** An output buffer for member info.
     */
    public ByteBuffer databuf = new ByteBuffer(DATA_BUF_SIZE);

    
An output buffer for the constant pool.
/** An output buffer for the constant pool.
     */
    ByteBuffer poolbuf = new ByteBuffer(CLASS_BUF_SIZE);

    
The constant pool writer.
/** The constant pool writer.
     */
    final PoolWriter poolWriter;

    
The log to use for verbose output.
/** The log to use for verbose output.
     */
    private final Log log;

    
The name table. /** The name table. */
    private final Names names;

    
Access to files. /** Access to files. */
    private final JavaFileManager fileManager;

    
The tags and constants used in compressed stackmap. /** The tags and constants used in compressed stackmap. */
    static final int SAME_FRAME_SIZE = 64;
    static final int SAME_LOCALS_1_STACK_ITEM_EXTENDED = 247;
    static final int SAME_FRAME_EXTENDED = 251;
    static final int FULL_FRAME = 255;
    static final int MAX_LOCAL_LENGTH_DIFF = 4;

    
Get the ClassWriter instance for this context. /** Get the ClassWriter instance for this context. */
    public static ClassWriter instance(Context context) {
        ClassWriter instance = context.get(classWriterKey);
        if (instance == null)
            instance = new ClassWriter(context);
        return instance;
    }

    
Construct a class writer, given an options table.
/** Construct a class writer, given an options table.
     */
    protected ClassWriter(Context context) {
        context.put(classWriterKey, this);

        log = Log.instance(context);
        names = Names.instance(context);
        options = Options.instance(context);
        preview = Preview.instance(context);
        target = Target.instance(context);
        source = Source.instance(context);
        types = Types.instance(context);
        check = Check.instance(context);
        fileManager = context.get(JavaFileManager.class);
        poolWriter = Gen.instance(context).poolWriter;

        verbose        = options.isSet(VERBOSE);
        genCrt         = options.isSet(XJCOV);
        debugstackmap = options.isSet("debug.stackmap");

        emitSourceFile = options.isUnset(G_CUSTOM) ||
                            options.isSet(G_CUSTOM, "source");

        String modifierFlags = options.get("debug.dumpmodifiers");
        if (modifierFlags != null) {
            dumpClassModifiers = modifierFlags.indexOf('c') != -1;
            dumpFieldModifiers = modifierFlags.indexOf('f') != -1;
            dumpInnerClassModifiers = modifierFlags.indexOf('i') != -1;
            dumpMethodModifiers = modifierFlags.indexOf('m') != -1;
        }
    }

    public void addExtraAttributes(ToIntFunction<Symbol> addExtraAttributes) {
        extraAttributeHooks = extraAttributeHooks.prepend(addExtraAttributes);
    }

/******************************************************************
 * Diagnostics: dump generated class names and modifiers
 ******************************************************************/

    
Value of option 'dumpmodifiers' is a string
 indicating which modifiers should be dumped for debugging:
   'c' -- classes
   'f' -- fields
   'i' -- innerclass attributes
   'm' -- methods
 For example, to dump everything:
   javac -XDdumpmodifiers=cifm MyProg.java
/** Value of option 'dumpmodifiers' is a string
     *  indicating which modifiers should be dumped for debugging:
     *    'c' -- classes
     *    'f' -- fields
     *    'i' -- innerclass attributes
     *    'm' -- methods
     *  For example, to dump everything:
     *    javac -XDdumpmodifiers=cifm MyProg.java
     */
    private boolean dumpClassModifiers; // -XDdumpmodifiers=c
    private boolean dumpFieldModifiers; // -XDdumpmodifiers=f
    private boolean dumpInnerClassModifiers; // -XDdumpmodifiers=i
    private boolean dumpMethodModifiers; // -XDdumpmodifiers=m


    
Return flags as a string, separated by " ".
/** Return flags as a string, separated by " ".
     */
    public static String flagNames(long flags) {
        StringBuilder sbuf = new StringBuilder();
        int i = 0;
        long f = flags & StandardFlags;
        while (f != 0) {
            if ((f & 1) != 0) {
                sbuf.append(" ");
                sbuf.append(flagName[i]);
            }
            f = f >> 1;
            i++;
        }
        return sbuf.toString();
    }
    //where
        private final static String[] flagName = {
            "PUBLIC", "PRIVATE", "PROTECTED", "STATIC", "FINAL",
            "SUPER", "VOLATILE", "TRANSIENT", "NATIVE", "INTERFACE",
            "ABSTRACT", "STRICTFP"};

/******************************************************************
 * Output routines
 ******************************************************************/

    
Write a character into given byte buffer;
 byte buffer will not be grown.
/** Write a character into given byte buffer;
     *  byte buffer will not be grown.
     */
    void putChar(ByteBuffer buf, int op, int x) {
        buf.elems[op  ] = (byte)((x >>  8) & 0xFF);
        buf.elems[op+1] = (byte)((x      ) & 0xFF);
    }

    
Write an integer into given byte buffer;
 byte buffer will not be grown.
/** Write an integer into given byte buffer;
     *  byte buffer will not be grown.
     */
    void putInt(ByteBuffer buf, int adr, int x) {
        buf.elems[adr  ] = (byte)((x >> 24) & 0xFF);
        buf.elems[adr+1] = (byte)((x >> 16) & 0xFF);
        buf.elems[adr+2] = (byte)((x >>  8) & 0xFF);
        buf.elems[adr+3] = (byte)((x      ) & 0xFF);
    }

/******************************************************************
 * Writing the Constant Pool
 ******************************************************************/

    
Thrown when the constant pool is over full.
/** Thrown when the constant pool is over full.
     */
    public static class PoolOverflow extends RuntimeException {
        private static final long serialVersionUID = 0;
        public PoolOverflow() {}
    }
    public static class StringOverflow extends RuntimeException {
        private static final long serialVersionUID = 0;
        public final String value;
        public StringOverflow(String s) {
            value = s;
        }
    }

/******************************************************************
 * Writing Attributes
 ******************************************************************/

    
Write header for an attribute to data buffer and return
 position past attribute length index.
/** Write header for an attribute to data buffer and return
     *  position past attribute length index.
     */
    public int writeAttr(Name attrName) {
        int index = poolWriter.putName(attrName);
        databuf.appendChar(index);
        databuf.appendInt(0);
        return databuf.length;
    }

    
Fill in attribute length.
/** Fill in attribute length.
     */
    public void endAttr(int index) {
        putInt(databuf, index - 4, databuf.length - index);
    }

    
Leave space for attribute count and return index for
 number of attributes field.
/** Leave space for attribute count and return index for
     *  number of attributes field.
     */
    int beginAttrs() {
        databuf.appendChar(0);
        return databuf.length;
    }

    
Fill in number of attributes.
/** Fill in number of attributes.
     */
    void endAttrs(int index, int count) {
        putChar(databuf, index - 2, count);
    }

    
Write the EnclosingMethod attribute if needed.
 Returns the number of attributes written (0 or 1).
/** Write the EnclosingMethod attribute if needed.
     *  Returns the number of attributes written (0 or 1).
     */
    int writeEnclosingMethodAttribute(ClassSymbol c) {
        return writeEnclosingMethodAttribute(names.EnclosingMethod, c);
    }

    
Write the EnclosingMethod attribute with a specified name.
 Returns the number of attributes written (0 or 1).
/** Write the EnclosingMethod attribute with a specified name.
     *  Returns the number of attributes written (0 or 1).
     */
    protected int writeEnclosingMethodAttribute(Name attributeName, ClassSymbol c) {
        if (c.owner.kind != MTH && // neither a local class
            c.name != names.empty) // nor anonymous
            return 0;

        int alenIdx = writeAttr(attributeName);
        ClassSymbol enclClass = c.owner.enclClass();
        MethodSymbol enclMethod =
            (c.owner.type == null // local to init block
             || c.owner.kind != MTH) // or member init
            ? null
            : ((MethodSymbol)c.owner).originalEnclosingMethod();
        databuf.appendChar(poolWriter.putClass(enclClass));
        databuf.appendChar(enclMethod == null ? 0 : poolWriter.putNameAndType(enclMethod));
        endAttr(alenIdx);
        return 1;
    }

    
Write flag attributes; return number of attributes written.
/** Write flag attributes; return number of attributes written.
     */
    int writeFlagAttrs(long flags) {
        int acount = 0;
        if ((flags & DEPRECATED) != 0) {
            int alenIdx = writeAttr(names.Deprecated);
            endAttr(alenIdx);
            acount++;
        }
        return acount;
    }

    
Write member (field or method) attributes;
 return number of attributes written.
/** Write member (field or method) attributes;
     *  return number of attributes written.
     */
    int writeMemberAttrs(Symbol sym, boolean isRecordComponent) {
        int acount = 0;
        if (!isRecordComponent) {
            acount = writeFlagAttrs(sym.flags());
        }
        long flags = sym.flags();
        if ((flags & (SYNTHETIC | BRIDGE)) != SYNTHETIC &&
            (flags & ANONCONSTR) == 0 &&
            (!types.isSameType(sym.type, sym.erasure(types)) ||
             poolWriter.signatureGen.hasTypeVar(sym.type.getThrownTypes()))) {
            // note that a local class with captured variables
            // will get a signature attribute
            int alenIdx = writeAttr(names.Signature);
            databuf.appendChar(poolWriter.putSignature(sym));
            endAttr(alenIdx);
            acount++;
        }
        acount += writeJavaAnnotations(sym.getRawAttributes());
        acount += writeTypeAnnotations(sym.getRawTypeAttributes(), false);
        return acount;
    }

    
Write method parameter names attribute.
/**
     * Write method parameter names attribute.
     */
    int writeMethodParametersAttr(MethodSymbol m) {
        MethodType ty = m.externalType(types).asMethodType();
        final int allparams = ty.argtypes.size();
        if (m.params != null && allparams != 0) {
            final int attrIndex = writeAttr(names.MethodParameters);
            databuf.appendByte(allparams);
            // Write extra parameters first
            for (VarSymbol s : m.extraParams) {
                final int flags =
                    ((int) s.flags() & (FINAL | SYNTHETIC | MANDATED)) |
                    ((int) m.flags() & SYNTHETIC);
                databuf.appendChar(poolWriter.putName(s.name));
                databuf.appendChar(flags);
            }
            // Now write the real parameters
            for (VarSymbol s : m.params) {
                final int flags =
                    ((int) s.flags() & (FINAL | SYNTHETIC | MANDATED)) |
                    ((int) m.flags() & SYNTHETIC);
                databuf.appendChar(poolWriter.putName(s.name));
                databuf.appendChar(flags);
            }
            // Now write the captured locals
            for (VarSymbol s : m.capturedLocals) {
                final int flags =
                    ((int) s.flags() & (FINAL | SYNTHETIC | MANDATED)) |
                    ((int) m.flags() & SYNTHETIC);
                databuf.appendChar(poolWriter.putName(s.name));
                databuf.appendChar(flags);
            }
            endAttr(attrIndex);
            return 1;
        } else
            return 0;
    }

    private void writeParamAnnotations(List<VarSymbol> params,
                                       RetentionPolicy retention) {
        databuf.appendByte(params.length());
        for (VarSymbol s : params) {
            ListBuffer<Attribute.Compound> buf = new ListBuffer<>();
            for (Attribute.Compound a : s.getRawAttributes())
                if (types.getRetention(a) == retention)
                    buf.append(a);
            databuf.appendChar(buf.length());
            for (Attribute.Compound a : buf)
                writeCompoundAttribute(a);
        }

    }

    private void writeParamAnnotations(MethodSymbol m,
                                       RetentionPolicy retention) {
        databuf.appendByte(m.params.length());
        writeParamAnnotations(m.params, retention);
    }

    
Write method parameter annotations;
 return number of attributes written.
/** Write method parameter annotations;
     *  return number of attributes written.
     */
    int writeParameterAttrs(List<VarSymbol> vars) {
        boolean hasVisible = false;
        boolean hasInvisible = false;
        if (vars != null) {
            for (VarSymbol s : vars) {
                for (Attribute.Compound a : s.getRawAttributes()) {
                    switch (types.getRetention(a)) {
                    case SOURCE: break;
                    case CLASS: hasInvisible = true; break;
                    case RUNTIME: hasVisible = true; break;
                    default: // /* fail soft */ throw new AssertionError(vis);
                    }
                }
            }
        }

        int attrCount = 0;
        if (hasVisible) {
            int attrIndex = writeAttr(names.RuntimeVisibleParameterAnnotations);
            writeParamAnnotations(vars, RetentionPolicy.RUNTIME);
            endAttr(attrIndex);
            attrCount++;
        }
        if (hasInvisible) {
            int attrIndex = writeAttr(names.RuntimeInvisibleParameterAnnotations);
            writeParamAnnotations(vars, RetentionPolicy.CLASS);
            endAttr(attrIndex);
            attrCount++;
        }
        return attrCount;
    }

/**********************************************************************
 * Writing Java-language annotations (aka metadata, attributes)
 **********************************************************************/

    
Write Java-language annotations; return number of JVM
 attributes written (zero or one).
/** Write Java-language annotations; return number of JVM
     *  attributes written (zero or one).
     */
    int writeJavaAnnotations(List<Attribute.Compound> attrs) {
        if (attrs.isEmpty()) return 0;
        ListBuffer<Attribute.Compound> visibles = new ListBuffer<>();
        ListBuffer<Attribute.Compound> invisibles = new ListBuffer<>();
        for (Attribute.Compound a : attrs) {
            switch (types.getRetention(a)) {
            case SOURCE: break;
            case CLASS: invisibles.append(a); break;
            case RUNTIME: visibles.append(a); break;
            default: // /* fail soft */ throw new AssertionError(vis);
            }
        }

        int attrCount = 0;
        if (visibles.length() != 0) {
            int attrIndex = writeAttr(names.RuntimeVisibleAnnotations);
            databuf.appendChar(visibles.length());
            for (Attribute.Compound a : visibles)
                writeCompoundAttribute(a);
            endAttr(attrIndex);
            attrCount++;
        }
        if (invisibles.length() != 0) {
            int attrIndex = writeAttr(names.RuntimeInvisibleAnnotations);
            databuf.appendChar(invisibles.length());
            for (Attribute.Compound a : invisibles)
                writeCompoundAttribute(a);
            endAttr(attrIndex);
            attrCount++;
        }
        return attrCount;
    }

    int writeTypeAnnotations(List<Attribute.TypeCompound> typeAnnos, boolean inCode) {
        if (typeAnnos.isEmpty()) return 0;

        ListBuffer<Attribute.TypeCompound> visibles = new ListBuffer<>();
        ListBuffer<Attribute.TypeCompound> invisibles = new ListBuffer<>();

        for (Attribute.TypeCompound tc : typeAnnos) {
            if (tc.hasUnknownPosition()) {
                boolean fixed = tc.tryFixPosition();

                // Could we fix it?
                if (!fixed) {
                    // This happens for nested types like @A Outer. @B Inner.
                    // For method parameters we get the annotation twice! Once with
                    // a valid position, once unknown.
                    // TODO: find a cleaner solution.
                    PrintWriter pw = log.getWriter(Log.WriterKind.ERROR);
                    pw.println("ClassWriter: Position UNKNOWN in type annotation: " + tc);
                    continue;
                }
            }

            if (tc.position.type.isLocal() != inCode)
                continue;
            if (!tc.position.emitToClassfile())
                continue;
            switch (types.getRetention(tc)) {
            case SOURCE: break;
            case CLASS: invisibles.append(tc); break;
            case RUNTIME: visibles.append(tc); break;
            default: // /* fail soft */ throw new AssertionError(vis);
            }
        }

        int attrCount = 0;
        if (visibles.length() != 0) {
            int attrIndex = writeAttr(names.RuntimeVisibleTypeAnnotations);
            databuf.appendChar(visibles.length());
            for (Attribute.TypeCompound p : visibles)
                writeTypeAnnotation(p);
            endAttr(attrIndex);
            attrCount++;
        }

        if (invisibles.length() != 0) {
            int attrIndex = writeAttr(names.RuntimeInvisibleTypeAnnotations);
            databuf.appendChar(invisibles.length());
            for (Attribute.TypeCompound p : invisibles)
                writeTypeAnnotation(p);
            endAttr(attrIndex);
            attrCount++;
        }

        return attrCount;
    }

    
A visitor to write an attribute including its leading
 single-character marker.
/** A visitor to write an attribute including its leading
     *  single-character marker.
     */
    class AttributeWriter implements Attribute.Visitor {
        public void visitConstant(Attribute.Constant _value) {
            if (_value.type.getTag() == CLASS) {
                Assert.check(_value.value instanceof String);
                String s = (String)_value.value;
                databuf.appendByte('s');
                databuf.appendChar(poolWriter.putName(names.fromString(s)));
            } else {
                switch (_value.type.getTag()) {
                    case BYTE:
                        databuf.appendByte('B');
                        break;
                    case CHAR:
                        databuf.appendByte('C');
                        break;
                    case SHORT:
                        databuf.appendByte('S');
                        break;
                    case INT:
                        databuf.appendByte('I');
                        break;
                    case LONG:
                        databuf.appendByte('J');
                        break;
                    case FLOAT:
                        databuf.appendByte('F');
                        break;
                    case DOUBLE:
                        databuf.appendByte('D');
                        break;
                    case BOOLEAN:
                        databuf.appendByte('Z');
                        break;
                    default:
                        throw new AssertionError(_value.type);
                }
                databuf.appendChar(poolWriter.putConstant(_value.value));
            }
        }
        public void visitEnum(Attribute.Enum e) {
            databuf.appendByte('e');
            databuf.appendChar(poolWriter.putDescriptor(e.value.type));
            databuf.appendChar(poolWriter.putName(e.value.name));
        }
        public void visitClass(Attribute.Class clazz) {
            databuf.appendByte('c');
            databuf.appendChar(poolWriter.putDescriptor(clazz.classType));
        }
        public void visitCompound(Attribute.Compound compound) {
            databuf.appendByte('@');
            writeCompoundAttribute(compound);
        }
        public void visitError(Attribute.Error x) {
            throw new AssertionError(x);
        }
        public void visitArray(Attribute.Array array) {
            databuf.appendByte('[');
            databuf.appendChar(array.values.length);
            for (Attribute a : array.values) {
                a.accept(this);
            }
        }
    }
    AttributeWriter awriter = new AttributeWriter();

    
Write a compound attribute excluding the '@' marker. /** Write a compound attribute excluding the '@' marker. */
    void writeCompoundAttribute(Attribute.Compound c) {
        databuf.appendChar(poolWriter.putDescriptor(c.type));
        databuf.appendChar(c.values.length());
        for (Pair<Symbol.MethodSymbol,Attribute> p : c.values) {
            databuf.appendChar(poolWriter.putName(p.fst.name));
            p.snd.accept(awriter);
        }
    }

    void writeTypeAnnotation(Attribute.TypeCompound c) {
        writePosition(c.position);
        writeCompoundAttribute(c);
    }

    void writePosition(TypeAnnotationPosition p) {
        databuf.appendByte(p.type.targetTypeValue()); // TargetType tag is a byte
        switch (p.type) {
        // instanceof
        case INSTANCEOF:
        // new expression
        case NEW:
        // constructor/method reference receiver
        case CONSTRUCTOR_REFERENCE:
        case METHOD_REFERENCE:
            databuf.appendChar(p.offset);
            break;
        // local variable
        case LOCAL_VARIABLE:
        // resource variable
        case RESOURCE_VARIABLE:
            databuf.appendChar(p.lvarOffset.length);  // for table length
            for (int i = 0; i < p.lvarOffset.length; ++i) {
                databuf.appendChar(p.lvarOffset[i]);
                databuf.appendChar(p.lvarLength[i]);
                databuf.appendChar(p.lvarIndex[i]);
            }
            break;
        // exception parameter
        case EXCEPTION_PARAMETER:
            databuf.appendChar(p.getExceptionIndex());
            break;
        // method receiver
        case METHOD_RECEIVER:
            // Do nothing
            break;
        // type parameter
        case CLASS_TYPE_PARAMETER:
        case METHOD_TYPE_PARAMETER:
            databuf.appendByte(p.parameter_index);
            break;
        // type parameter bound
        case CLASS_TYPE_PARAMETER_BOUND:
        case METHOD_TYPE_PARAMETER_BOUND:
            databuf.appendByte(p.parameter_index);
            databuf.appendByte(p.bound_index);
            break;
        // class extends or implements clause
        case CLASS_EXTENDS:
            databuf.appendChar(p.type_index);
            break;
        // throws
        case THROWS:
            databuf.appendChar(p.type_index);
            break;
        // method parameter
        case METHOD_FORMAL_PARAMETER:
            databuf.appendByte(p.parameter_index);
            break;
        // type cast
        case CAST:
        // method/constructor/reference type argument
        case CONSTRUCTOR_INVOCATION_TYPE_ARGUMENT:
        case METHOD_INVOCATION_TYPE_ARGUMENT:
        case CONSTRUCTOR_REFERENCE_TYPE_ARGUMENT:
        case METHOD_REFERENCE_TYPE_ARGUMENT:
            databuf.appendChar(p.offset);
            databuf.appendByte(p.type_index);
            break;
        // We don't need to worry about these
        case METHOD_RETURN:
        case FIELD:
            break;
        case UNKNOWN:
            throw new AssertionError("jvm.ClassWriter: UNKNOWN target type should never occur!");
        default:
            throw new AssertionError("jvm.ClassWriter: Unknown target type for position: " + p);
        }

        { // Append location data for generics/arrays.
            databuf.appendByte(p.location.size());
            java.util.List<Integer> loc = TypeAnnotationPosition.getBinaryFromTypePath(p.location);
            for (int i : loc)
                databuf.appendByte((byte)i);
        }
    }

/**********************************************************************
 * Writing module attributes
 **********************************************************************/

    
Write the Module attribute if needed.
 Returns the number of attributes written (0 or 1).
/** Write the Module attribute if needed.
     *  Returns the number of attributes written (0 or 1).
     */
    int writeModuleAttribute(ClassSymbol c) {
        ModuleSymbol m = (ModuleSymbol) c.owner;

        int alenIdx = writeAttr(names.Module);

        databuf.appendChar(poolWriter.putModule(m));
        databuf.appendChar(ModuleFlags.value(m.flags)); // module_flags
        databuf.appendChar(m.version != null ? poolWriter.putName(m.version) : 0);

        ListBuffer<RequiresDirective> requires = new ListBuffer<>();
        for (RequiresDirective r: m.requires) {
            if (!r.flags.contains(RequiresFlag.EXTRA))
                requires.add(r);
        }
        databuf.appendChar(requires.size());
        for (RequiresDirective r: requires) {
            databuf.appendChar(poolWriter.putModule(r.module));
            databuf.appendChar(RequiresFlag.value(r.flags));
            databuf.appendChar(r.module.version != null ? poolWriter.putName(r.module.version) : 0);
        }

        List<ExportsDirective> exports = m.exports;
        databuf.appendChar(exports.size());
        for (ExportsDirective e: exports) {
            databuf.appendChar(poolWriter.putPackage(e.packge));
            databuf.appendChar(ExportsFlag.value(e.flags));
            if (e.modules == null) {
                databuf.appendChar(0);
            } else {
                databuf.appendChar(e.modules.size());
                for (ModuleSymbol msym: e.modules) {
                    databuf.appendChar(poolWriter.putModule(msym));
                }
            }
        }

        List<OpensDirective> opens = m.opens;
        databuf.appendChar(opens.size());
        for (OpensDirective o: opens) {
            databuf.appendChar(poolWriter.putPackage(o.packge));
            databuf.appendChar(OpensFlag.value(o.flags));
            if (o.modules == null) {
                databuf.appendChar(0);
            } else {
                databuf.appendChar(o.modules.size());
                for (ModuleSymbol msym: o.modules) {
                    databuf.appendChar(poolWriter.putModule(msym));
                }
            }
        }

        List<UsesDirective> uses = m.uses;
        databuf.appendChar(uses.size());
        for (UsesDirective s: uses) {
            databuf.appendChar(poolWriter.putClass(s.service));
        }

        // temporary fix to merge repeated provides clause for same service;
        // eventually this should be disallowed when analyzing the module,
        // so that each service type only appears once.
        Map<ClassSymbol, Set<ClassSymbol>> mergedProvides = new LinkedHashMap<>();
        for (ProvidesDirective p : m.provides) {
            mergedProvides.computeIfAbsent(p.service, s -> new LinkedHashSet<>()).addAll(p.impls);
        }
        databuf.appendChar(mergedProvides.size());
        mergedProvides.forEach((srvc, impls) -> {
            databuf.appendChar(poolWriter.putClass(srvc));
            databuf.appendChar(impls.size());
            impls.forEach(impl -> databuf.appendChar(poolWriter.putClass(impl)));
        });

        endAttr(alenIdx);
        return 1;
    }

/**********************************************************************
 * Writing Objects
 **********************************************************************/

    
Write "inner classes" attribute.
/** Write "inner classes" attribute.
     */
    void writeInnerClasses() {
        int alenIdx = writeAttr(names.InnerClasses);
        databuf.appendChar(poolWriter.innerClasses.size());
        for (ClassSymbol inner : poolWriter.innerClasses) {
            inner.markAbstractIfNeeded(types);
            char flags = (char) adjustFlags(inner.flags_field);
            if ((flags & INTERFACE) != 0) flags |= ABSTRACT; // Interfaces are always ABSTRACT
            flags &= ~STRICTFP; //inner classes should not have the strictfp flag set.
            if (dumpInnerClassModifiers) {
                PrintWriter pw = log.getWriter(Log.WriterKind.ERROR);
                pw.println("INNERCLASS  " + inner.name);
                pw.println("---" + flagNames(flags));
            }
            databuf.appendChar(poolWriter.putClass(inner));
            databuf.appendChar(
                inner.owner.kind == TYP && !inner.name.isEmpty() ? poolWriter.putClass((ClassSymbol)inner.owner) : 0);
            databuf.appendChar(
                !inner.name.isEmpty() ? poolWriter.putName(inner.name) : 0);
            databuf.appendChar(flags);
        }
        endAttr(alenIdx);
    }

    int writeRecordAttribute(ClassSymbol csym) {
        int alenIdx = writeAttr(names.Record);
        Scope s = csym.members();
        databuf.appendChar(csym.getRecordComponents().size());
        for (VarSymbol v: csym.getRecordComponents()) {
            //databuf.appendChar(poolWriter.putMember(v.accessor.head.snd));
            databuf.appendChar(poolWriter.putName(v.name));
            databuf.appendChar(poolWriter.putDescriptor(v));
            int acountIdx = beginAttrs();
            int acount = 0;
            acount += writeMemberAttrs(v, true);
            endAttrs(acountIdx, acount);
        }
        endAttr(alenIdx);
        return 1;
    }

    
Write NestMembers attribute (if needed)
/**
     * Write NestMembers attribute (if needed)
     */
    int writeNestMembersIfNeeded(ClassSymbol csym) {
        ListBuffer<ClassSymbol> nested = new ListBuffer<>();
        listNested(csym, nested);
        Set<ClassSymbol> nestedUnique = new LinkedHashSet<>(nested);
        if (csym.owner.kind == PCK && !nestedUnique.isEmpty()) {
            int alenIdx = writeAttr(names.NestMembers);
            databuf.appendChar(nestedUnique.size());
            for (ClassSymbol s : nestedUnique) {
                databuf.appendChar(poolWriter.putClass(s));
            }
            endAttr(alenIdx);
            return 1;
        }
        return 0;
    }

    
Write NestHost attribute (if needed)
/**
     * Write NestHost attribute (if needed)
     */
    int writeNestHostIfNeeded(ClassSymbol csym) {
        if (csym.owner.kind != PCK) {
            int alenIdx = writeAttr(names.NestHost);
            databuf.appendChar(poolWriter.putClass(csym.outermostClass()));
            endAttr(alenIdx);
            return 1;
        }
        return 0;
    }

    private void listNested(Symbol sym, ListBuffer<ClassSymbol> seen) {
        if (sym.kind != TYP) return;
        ClassSymbol csym = (ClassSymbol)sym;
        if (csym.owner.kind != PCK) {
            seen.add(csym);
        }
        if (csym.members() != null) {
            for (Symbol s : sym.members().getSymbols()) {
                listNested(s, seen);
            }
        }
        if (csym.trans_local != null) {
            for (Symbol s : csym.trans_local) {
                listNested(s, seen);
            }
        }
    }

    
Write "bootstrapMethods" attribute.
/** Write "bootstrapMethods" attribute.
     */
    void writeBootstrapMethods() {
        int alenIdx = writeAttr(names.BootstrapMethods);
        databuf.appendChar(poolWriter.bootstrapMethods.size());
        for (BsmKey bsmKey : poolWriter.bootstrapMethods.keySet()) {
            //write BSM handle
            databuf.appendChar(poolWriter.putConstant(bsmKey.bsm));
            LoadableConstant[] uniqueArgs = bsmKey.staticArgs;
            //write static args length
            databuf.appendChar(uniqueArgs.length);
            //write static args array
            for (LoadableConstant arg : uniqueArgs) {
                databuf.appendChar(poolWriter.putConstant(arg));
            }
        }
        endAttr(alenIdx);
    }

    
Write field symbol, entering all references into constant pool.
/** Write field symbol, entering all references into constant pool.
     */
    void writeField(VarSymbol v) {
        int flags = adjustFlags(v.flags());
        databuf.appendChar(flags);
        if (dumpFieldModifiers) {
            PrintWriter pw = log.getWriter(Log.WriterKind.ERROR);
            pw.println("FIELD  " + v.name);
            pw.println("---" + flagNames(v.flags()));
        }
        databuf.appendChar(poolWriter.putName(v.name));
        databuf.appendChar(poolWriter.putDescriptor(v));
        int acountIdx = beginAttrs();
        int acount = 0;
        if (v.getConstValue() != null) {
            int alenIdx = writeAttr(names.ConstantValue);
            databuf.appendChar(poolWriter.putConstant(v.getConstValue()));
            endAttr(alenIdx);
            acount++;
        }
        acount += writeMemberAttrs(v, false);
        acount += writeExtraAttributes(v);
        endAttrs(acountIdx, acount);
    }

    
Write method symbol, entering all references into constant pool.
/** Write method symbol, entering all references into constant pool.
     */
    void writeMethod(MethodSymbol m) {
        int flags = adjustFlags(m.flags());
        databuf.appendChar(flags);
        if (dumpMethodModifiers) {
            PrintWriter pw = log.getWriter(Log.WriterKind.ERROR);
            pw.println("METHOD  " + m.name);
            pw.println("---" + flagNames(m.flags()));
        }
        databuf.appendChar(poolWriter.putName(m.name));
        databuf.appendChar(poolWriter.putDescriptor(m));
        int acountIdx = beginAttrs();
        int acount = 0;
        if (m.code != null) {
            int alenIdx = writeAttr(names.Code);
            writeCode(m.code);
            m.code = null; // to conserve space
            endAttr(alenIdx);
            acount++;
        }
        List<Type> thrown = m.erasure(types).getThrownTypes();
        if (thrown.nonEmpty()) {
            int alenIdx = writeAttr(names.Exceptions);
            databuf.appendChar(thrown.length());
            for (List<Type> l = thrown; l.nonEmpty(); l = l.tail)
                databuf.appendChar(poolWriter.putClass(l.head));
            endAttr(alenIdx);
            acount++;
        }
        if (m.defaultValue != null) {
            int alenIdx = writeAttr(names.AnnotationDefault);
            m.defaultValue.accept(awriter);
            endAttr(alenIdx);
            acount++;
        }
        if (target.hasMethodParameters() && (options.isSet(PARAMETERS) || m.isConstructor() && (m.flags_field & RECORD) != 0)) {
            if (!m.isLambdaMethod()) // Per JDK-8138729, do not emit parameters table for lambda bodies.
                acount += writeMethodParametersAttr(m);
        }
        acount += writeMemberAttrs(m, false);
        if (!m.isLambdaMethod())
            acount += writeParameterAttrs(m.params);
        acount += writeExtraAttributes(m);
        endAttrs(acountIdx, acount);
    }

    
Write code attribute of method.
/** Write code attribute of method.
     */
    void writeCode(Code code) {
        databuf.appendChar(code.max_stack);
        databuf.appendChar(code.max_locals);
        databuf.appendInt(code.cp);
        databuf.appendBytes(code.code, 0, code.cp);
        databuf.appendChar(code.catchInfo.length());
        for (List<char[]> l = code.catchInfo.toList();
             l.nonEmpty();
             l = l.tail) {
            for (int i = 0; i < l.head.length; i++)
                databuf.appendChar(l.head[i]);
        }
        int acountIdx = beginAttrs();
        int acount = 0;

        if (code.lineInfo.nonEmpty()) {
            int alenIdx = writeAttr(names.LineNumberTable);
            databuf.appendChar(code.lineInfo.length());
            for (List<char[]> l = code.lineInfo.reverse();
                 l.nonEmpty();
                 l = l.tail)
                for (int i = 0; i < l.head.length; i++)
                    databuf.appendChar(l.head[i]);
            endAttr(alenIdx);
            acount++;
        }

        if (genCrt && (code.crt != null)) {
            CRTable crt = code.crt;
            int alenIdx = writeAttr(names.CharacterRangeTable);
            int crtIdx = beginAttrs();
            int crtEntries = crt.writeCRT(databuf, code.lineMap, log);
            endAttrs(crtIdx, crtEntries);
            endAttr(alenIdx);
            acount++;
        }

        // counter for number of generic local variables
        if (code.varDebugInfo && code.varBufferSize > 0) {
            int nGenericVars = 0;
            int alenIdx = writeAttr(names.LocalVariableTable);
            databuf.appendChar(code.getLVTSize());
            for (int i=0; i<code.varBufferSize; i++) {
                Code.LocalVar var = code.varBuffer[i];

                for (Code.LocalVar.Range r: var.aliveRanges) {
                    // write variable info
                    Assert.check(r.start_pc >= 0
                            && r.start_pc <= code.cp);
                    databuf.appendChar(r.start_pc);
                    Assert.check(r.length > 0
                            && (r.start_pc + r.length) <= code.cp);
                    databuf.appendChar(r.length);
                    VarSymbol sym = var.sym;
                    databuf.appendChar(poolWriter.putName(sym.name));
                    databuf.appendChar(poolWriter.putDescriptor(sym));
                    databuf.appendChar(var.reg);
                    if (needsLocalVariableTypeEntry(var.sym.type)) {
                        nGenericVars++;
                    }
                }
            }
            endAttr(alenIdx);
            acount++;

            if (nGenericVars > 0) {
                alenIdx = writeAttr(names.LocalVariableTypeTable);
                databuf.appendChar(nGenericVars);
                int count = 0;

                for (int i=0; i<code.varBufferSize; i++) {
                    Code.LocalVar var = code.varBuffer[i];
                    VarSymbol sym = var.sym;
                    if (!needsLocalVariableTypeEntry(sym.type))
                        continue;
                    for (Code.LocalVar.Range r : var.aliveRanges) {
                        // write variable info
                        databuf.appendChar(r.start_pc);
                        databuf.appendChar(r.length);
                        databuf.appendChar(poolWriter.putName(sym.name));
                        databuf.appendChar(poolWriter.putSignature(sym));
                        databuf.appendChar(var.reg);
                        count++;
                    }
                }
                Assert.check(count == nGenericVars);
                endAttr(alenIdx);
                acount++;
            }
        }

        if (code.stackMapBufferSize > 0) {
            if (debugstackmap) System.out.println("Stack map for " + code.meth);
            int alenIdx = writeAttr(code.stackMap.getAttributeName(names));
            writeStackMap(code);
            endAttr(alenIdx);
            acount++;
        }

        acount += writeTypeAnnotations(code.meth.getRawTypeAttributes(), true);

        endAttrs(acountIdx, acount);
    }
    //where
    private boolean needsLocalVariableTypeEntry(Type t) {
        //a local variable needs a type-entry if its type T is generic
        //(i.e. |T| != T) and if it's not an non-denotable type (non-denotable
        // types are not supported in signature attribute grammar!)
        return !types.isSameType(t, types.erasure(t)) &&
                check.checkDenotable(t);
    }

    void writeStackMap(Code code) {
        int nframes = code.stackMapBufferSize;
        if (debugstackmap) System.out.println(" nframes = " + nframes);
        databuf.appendChar(nframes);

        switch (code.stackMap) {
        case CLDC:
            for (int i=0; i<nframes; i++) {
                if (debugstackmap) System.out.print("  " + i + ":");
                Code.StackMapFrame frame = code.stackMapBuffer[i];

                // output PC
                if (debugstackmap) System.out.print(" pc=" + frame.pc);
                databuf.appendChar(frame.pc);

                // output locals
                int localCount = 0;
                for (int j=0; j<frame.locals.length;
                     j += Code.width(frame.locals[j])) {
                    localCount++;
                }
                if (debugstackmap) System.out.print(" nlocals=" +
                                                    localCount);
                databuf.appendChar(localCount);
                for (int j=0; j<frame.locals.length;
                     j += Code.width(frame.locals[j])) {
                    if (debugstackmap) System.out.print(" local[" + j + "]=");
                    writeStackMapType(frame.locals[j]);
                }

                // output stack
                int stackCount = 0;
                for (int j=0; j<frame.stack.length;
                     j += Code.width(frame.stack[j])) {
                    stackCount++;
                }
                if (debugstackmap) System.out.print(" nstack=" +
                                                    stackCount);
                databuf.appendChar(stackCount);
                for (int j=0; j<frame.stack.length;
                     j += Code.width(frame.stack[j])) {
                    if (debugstackmap) System.out.print(" stack[" + j + "]=");
                    writeStackMapType(frame.stack[j]);
                }
                if (debugstackmap) System.out.println();
            }
            break;
        case JSR202: {
            Assert.checkNull(code.stackMapBuffer);
            for (int i=0; i<nframes; i++) {
                if (debugstackmap) System.out.print("  " + i + ":");
                StackMapTableFrame frame = code.stackMapTableBuffer[i];
                frame.write(this);
                if (debugstackmap) System.out.println();
            }
            break;
        }
        default:
            throw new AssertionError("Unexpected stackmap format value");
        }
    }

        //where
        void writeStackMapType(Type t) {
            if (t == null) {
                if (debugstackmap) System.out.print("empty");
                databuf.appendByte(0);
            }
            else switch(t.getTag()) {
            case BYTE:
            case CHAR:
            case SHORT:
            case INT:
            case BOOLEAN:
                if (debugstackmap) System.out.print("int");
                databuf.appendByte(1);
                break;
            case FLOAT:
                if (debugstackmap) System.out.print("float");
                databuf.appendByte(2);
                break;
            case DOUBLE:
                if (debugstackmap) System.out.print("double");
                databuf.appendByte(3);
                break;
            case LONG:
                if (debugstackmap) System.out.print("long");
                databuf.appendByte(4);
                break;
            case BOT: // null
                if (debugstackmap) System.out.print("null");
                databuf.appendByte(5);
                break;
            case CLASS:
            case ARRAY:
            case TYPEVAR:
                if (debugstackmap) System.out.print("object(" + types.erasure(t).tsym + ")");
                databuf.appendByte(7);
                databuf.appendChar(poolWriter.putClass(types.erasure(t)));
                break;
            case UNINITIALIZED_THIS:
                if (debugstackmap) System.out.print("uninit_this");
                databuf.appendByte(6);
                break;
            case UNINITIALIZED_OBJECT:
                { UninitializedType uninitType = (UninitializedType)t;
                databuf.appendByte(8);
                if (debugstackmap) System.out.print("uninit_object@" + uninitType.offset);
                databuf.appendChar(uninitType.offset);
                }
                break;
            default:
                throw new AssertionError();
            }
        }

    
An entry in the JSR202 StackMapTable /** An entry in the JSR202 StackMapTable */
    abstract static class StackMapTableFrame {
        abstract int getFrameType();

        void write(ClassWriter writer) {
            int frameType = getFrameType();
            writer.databuf.appendByte(frameType);
            if (writer.debugstackmap) System.out.print(" frame_type=" + frameType);
        }

        static class SameFrame extends StackMapTableFrame {
            final int offsetDelta;
            SameFrame(int offsetDelta) {
                this.offsetDelta = offsetDelta;
            }
            int getFrameType() {
                return (offsetDelta < SAME_FRAME_SIZE) ? offsetDelta : SAME_FRAME_EXTENDED;
            }
            @Override
            void write(ClassWriter writer) {
                super.write(writer);
                if (getFrameType() == SAME_FRAME_EXTENDED) {
                    writer.databuf.appendChar(offsetDelta);
                    if (writer.debugstackmap){
                        System.out.print(" offset_delta=" + offsetDelta);
                    }
                }
            }
        }

        static class SameLocals1StackItemFrame extends StackMapTableFrame {
            final int offsetDelta;
            final Type stack;
            SameLocals1StackItemFrame(int offsetDelta, Type stack) {
                this.offsetDelta = offsetDelta;
                this.stack = stack;
            }
            int getFrameType() {
                return (offsetDelta < SAME_FRAME_SIZE) ?
                       (SAME_FRAME_SIZE + offsetDelta) :
                       SAME_LOCALS_1_STACK_ITEM_EXTENDED;
            }
            @Override
            void write(ClassWriter writer) {
                super.write(writer);
                if (getFrameType() == SAME_LOCALS_1_STACK_ITEM_EXTENDED) {
                    writer.databuf.appendChar(offsetDelta);
                    if (writer.debugstackmap) {
                        System.out.print(" offset_delta=" + offsetDelta);
                    }
                }
                if (writer.debugstackmap) {
                    System.out.print(" stack[" + 0 + "]=");
                }
                writer.writeStackMapType(stack);
            }
        }

        static class ChopFrame extends StackMapTableFrame {
            final int frameType;
            final int offsetDelta;
            ChopFrame(int frameType, int offsetDelta) {
                this.frameType = frameType;
                this.offsetDelta = offsetDelta;
            }
            int getFrameType() { return frameType; }
            @Override
            void write(ClassWriter writer) {
                super.write(writer);
                writer.databuf.appendChar(offsetDelta);
                if (writer.debugstackmap) {
                    System.out.print(" offset_delta=" + offsetDelta);
                }
            }
        }

        static class AppendFrame extends StackMapTableFrame {
            final int frameType;
            final int offsetDelta;
            final Type[] locals;
            AppendFrame(int frameType, int offsetDelta, Type[] locals) {
                this.frameType = frameType;
                this.offsetDelta = offsetDelta;
                this.locals = locals;
            }
            int getFrameType() { return frameType; }
            @Override
            void write(ClassWriter writer) {
                super.write(writer);
                writer.databuf.appendChar(offsetDelta);
                if (writer.debugstackmap) {
                    System.out.print(" offset_delta=" + offsetDelta);
                }
                for (int i=0; i<locals.length; i++) {
                     if (writer.debugstackmap) System.out.print(" locals[" + i + "]=");
                     writer.writeStackMapType(locals[i]);
                }
            }
        }

        static class FullFrame extends StackMapTableFrame {
            final int offsetDelta;
            final Type[] locals;
            final Type[] stack;
            FullFrame(int offsetDelta, Type[] locals, Type[] stack) {
                this.offsetDelta = offsetDelta;
                this.locals = locals;
                this.stack = stack;
            }
            int getFrameType() { return FULL_FRAME; }
            @Override
            void write(ClassWriter writer) {
                super.write(writer);
                writer.databuf.appendChar(offsetDelta);
                writer.databuf.appendChar(locals.length);
                if (writer.debugstackmap) {
                    System.out.print(" offset_delta=" + offsetDelta);
                    System.out.print(" nlocals=" + locals.length);
                }
                for (int i=0; i<locals.length; i++) {
                    if (writer.debugstackmap) System.out.print(" locals[" + i + "]=");
                    writer.writeStackMapType(locals[i]);
                }

                writer.databuf.appendChar(stack.length);
                if (writer.debugstackmap) { System.out.print(" nstack=" + stack.length); }
                for (int i=0; i<stack.length; i++) {
                    if (writer.debugstackmap) System.out.print(" stack[" + i + "]=");
                    writer.writeStackMapType(stack[i]);
                }
            }
        }

       
Compare this frame with the previous frame and produce
 an entry of compressed stack map frame. /** Compare this frame with the previous frame and produce
        *  an entry of compressed stack map frame. */
        static StackMapTableFrame getInstance(Code.StackMapFrame this_frame,
                                              int prev_pc,
                                              Type[] prev_locals,
                                              Types types) {
            Type[] locals = this_frame.locals;
            Type[] stack = this_frame.stack;
            int offset_delta = this_frame.pc - prev_pc - 1;
            if (stack.length == 1) {
                if (locals.length == prev_locals.length
                    && compare(prev_locals, locals, types) == 0) {
                    return new SameLocals1StackItemFrame(offset_delta, stack[0]);
                }
            } else if (stack.length == 0) {
                int diff_length = compare(prev_locals, locals, types);
                if (diff_length == 0) {
                    return new SameFrame(offset_delta);
                } else if (-MAX_LOCAL_LENGTH_DIFF < diff_length && diff_length < 0) {
                    // APPEND
                    Type[] local_diff = new Type[-diff_length];
                    for (int i=prev_locals.length, j=0; i<locals.length; i++,j++) {
                        local_diff[j] = locals[i];
                    }
                    return new AppendFrame(SAME_FRAME_EXTENDED - diff_length,
                                           offset_delta,
                                           local_diff);
                } else if (0 < diff_length && diff_length < MAX_LOCAL_LENGTH_DIFF) {
                    // CHOP
                    return new ChopFrame(SAME_FRAME_EXTENDED - diff_length,
                                         offset_delta);
                }
            }
            // FULL_FRAME
            return new FullFrame(offset_delta, locals, stack);
        }

        static boolean isInt(Type t) {
            return (t.getTag().isStrictSubRangeOf(INT)  || t.hasTag(BOOLEAN));
        }

        static boolean isSameType(Type t1, Type t2, Types types) {
            if (t1 == null) { return t2 == null; }
            if (t2 == null) { return false; }

            if (isInt(t1) && isInt(t2)) { return true; }

            if (t1.hasTag(UNINITIALIZED_THIS)) {
                return t2.hasTag(UNINITIALIZED_THIS);
            } else if (t1.hasTag(UNINITIALIZED_OBJECT)) {
                if (t2.hasTag(UNINITIALIZED_OBJECT)) {
                    return ((UninitializedType)t1).offset == ((UninitializedType)t2).offset;
                } else {
                    return false;
                }
            } else if (t2.hasTag(UNINITIALIZED_THIS) || t2.hasTag(UNINITIALIZED_OBJECT)) {
                return false;
            }

            return types.isSameType(t1, t2);
        }

        static int compare(Type[] arr1, Type[] arr2, Types types) {
            int diff_length = arr1.length - arr2.length;
            if (diff_length > MAX_LOCAL_LENGTH_DIFF || diff_length < -MAX_LOCAL_LENGTH_DIFF) {
                return Integer.MAX_VALUE;
            }
            int len = (diff_length > 0) ? arr2.length : arr1.length;
            for (int i=0; i<len; i++) {
                if (!isSameType(arr1[i], arr2[i], types)) {
                    return Integer.MAX_VALUE;
                }
            }
            return diff_length;
        }
    }

    void writeFields(Scope s) {
        // process them in reverse sibling order;
        // i.e., process them in declaration order.
        List<VarSymbol> vars = List.nil();
        for (Symbol sym : s.getSymbols(NON_RECURSIVE)) {
            if (sym.kind == VAR) vars = vars.prepend((VarSymbol)sym);
        }
        while (vars.nonEmpty()) {
            writeField(vars.head);
            vars = vars.tail;
        }
    }

    void writeMethods(Scope s) {
        List<MethodSymbol> methods = List.nil();
        for (Symbol sym : s.getSymbols(NON_RECURSIVE)) {
            if (sym.kind == MTH && (sym.flags() & HYPOTHETICAL) == 0)
                methods = methods.prepend((MethodSymbol)sym);
        }
        while (methods.nonEmpty()) {
            writeMethod(methods.head);
            methods = methods.tail;
        }
    }

    
Emit a class file for a given class.
 @param c      The class from which a class file is generated.
/** Emit a class file for a given class.
     *  @param c      The class from which a class file is generated.
     */
    public JavaFileObject writeClass(ClassSymbol c)
        throws IOException, PoolOverflow, StringOverflow
    {
        String name = (c.owner.kind == MDL ? c.name : c.flatname).toString();
        Location outLocn;
        if (multiModuleMode) {
            ModuleSymbol msym = c.owner.kind == MDL ? (ModuleSymbol) c.owner : c.packge().modle;
            outLocn = fileManager.getLocationForModule(CLASS_OUTPUT, msym.name.toString());
        } else {
            outLocn = CLASS_OUTPUT;
        }
        JavaFileObject outFile
            = fileManager.getJavaFileForOutput(outLocn,
                                               name,
                                               JavaFileObject.Kind.CLASS,
                                               c.sourcefile);
        OutputStream out = outFile.openOutputStream();
        try {
            writeClassFile(out, c);
            if (verbose)
                log.printVerbose("wrote.file", outFile.getName());
            out.close();
            out = null;
        } catch (InvalidSignatureException ex) {
            log.error(Errors.CannotGenerateClass(c, Fragments.IllegalSignature(c, ex.type())));
        } finally {
            if (out != null) {
                // if we are propagating an exception, delete the file
                out.close();
                outFile.delete();
                outFile = null;
            }
        }
        return outFile; // may be null if write failed
    }

    
Write class `c' to outstream `out'.
/** Write class `c' to outstream `out'.
     */
    public void writeClassFile(OutputStream out, ClassSymbol c)
        throws IOException, PoolOverflow, StringOverflow {
        Assert.check((c.flags() & COMPOUND) == 0);
        databuf.reset();
        poolbuf.reset();

        Type supertype = types.supertype(c.type);
        List<Type> interfaces = types.interfaces(c.type);
        List<Type> typarams = c.type.getTypeArguments();

        int flags;
        if (c.owner.kind == MDL) {
            flags = ACC_MODULE;
        } else {
            flags = adjustFlags(c.flags() & ~DEFAULT);
            if ((flags & PROTECTED) != 0) flags |= PUBLIC;
            flags = flags & ClassFlags & ~STRICTFP;
            if ((flags & INTERFACE) == 0) flags |= ACC_SUPER;
        }

        if (dumpClassModifiers) {
            PrintWriter pw = log.getWriter(Log.WriterKind.ERROR);
            pw.println();
            pw.println("CLASSFILE  " + c.getQualifiedName());
            pw.println("---" + flagNames(flags));
        }
        databuf.appendChar(flags);

        if (c.owner.kind == MDL) {
            PackageSymbol unnamed = ((ModuleSymbol) c.owner).unnamedPackage;
            databuf.appendChar(poolWriter.putClass(new ClassSymbol(0, names.module_info, unnamed)));
        } else {
            databuf.appendChar(poolWriter.putClass(c));
        }
        databuf.appendChar(supertype.hasTag(CLASS) ? poolWriter.putClass((ClassSymbol)supertype.tsym) : 0);
        databuf.appendChar(interfaces.length());
        for (List<Type> l = interfaces; l.nonEmpty(); l = l.tail)
            databuf.appendChar(poolWriter.putClass((ClassSymbol)l.head.tsym));
        int fieldsCount = 0;
        int methodsCount = 0;
        for (Symbol sym : c.members().getSymbols(NON_RECURSIVE)) {
            switch (sym.kind) {
            case VAR: fieldsCount++; break;
            case MTH: if ((sym.flags() & HYPOTHETICAL) == 0) methodsCount++;
                      break;
            case TYP: poolWriter.enterInner((ClassSymbol)sym); break;
            default : Assert.error();
            }
        }

        if (c.trans_local != null) {
            for (ClassSymbol local : c.trans_local) {
                poolWriter.enterInner(local);
            }
        }

        databuf.appendChar(fieldsCount);
        writeFields(c.members());
        databuf.appendChar(methodsCount);
        writeMethods(c.members());

        int acountIdx = beginAttrs();
        int acount = 0;

        boolean sigReq =
            typarams.length() != 0 || supertype.allparams().length() != 0;
        for (List<Type> l = interfaces; !sigReq && l.nonEmpty(); l = l.tail)
            sigReq = l.head.allparams().length() != 0;
        if (sigReq) {
            int alenIdx = writeAttr(names.Signature);
            databuf.appendChar(poolWriter.putSignature(c));
            endAttr(alenIdx);
            acount++;
        }

        if (c.sourcefile != null && emitSourceFile) {
            int alenIdx = writeAttr(names.SourceFile);
            // WHM 6/29/1999: Strip file path prefix.  We do it here at
            // the last possible moment because the sourcefile may be used
            // elsewhere in error diagnostics. Fixes 4241573.
            String simpleName = PathFileObject.getSimpleName(c.sourcefile);
            databuf.appendChar(poolWriter.putName(names.fromString(simpleName)));
            endAttr(alenIdx);
            acount++;
        }

        if (genCrt) {
            // Append SourceID attribute
            int alenIdx = writeAttr(names.SourceID);
            databuf.appendChar(poolWriter.putName(names.fromString(Long.toString(getLastModified(c.sourcefile)))));
            endAttr(alenIdx);
            acount++;
            // Append CompilationID attribute
            alenIdx = writeAttr(names.CompilationID);
            databuf.appendChar(poolWriter.putName(names.fromString(Long.toString(System.currentTimeMillis()))));
            endAttr(alenIdx);
            acount++;
        }

        acount += writeFlagAttrs(c.flags());
        acount += writeJavaAnnotations(c.getRawAttributes());
        acount += writeTypeAnnotations(c.getRawTypeAttributes(), false);
        acount += writeEnclosingMethodAttribute(c);
        if (c.owner.kind == MDL) {
            acount += writeModuleAttribute(c);
            acount += writeFlagAttrs(c.owner.flags() & ~DEPRECATED);
        }
        acount += writeExtraClassAttributes(c);
        acount += writeExtraAttributes(c);

        poolbuf.appendInt(JAVA_MAGIC);
        if (preview.isEnabled()) {
            poolbuf.appendChar(ClassFile.PREVIEW_MINOR_VERSION);
        } else {
            poolbuf.appendChar(target.minorVersion);
        }
        poolbuf.appendChar(target.majorVersion);

        if (c.owner.kind != MDL) {
            if (target.hasNestmateAccess()) {
                acount += writeNestMembersIfNeeded(c);
                acount += writeNestHostIfNeeded(c);
            }
        }

        if (c.isRecord()) {
            acount += writeRecordAttribute(c);
        }

        if (!poolWriter.bootstrapMethods.isEmpty()) {
            writeBootstrapMethods();
            acount++;
        }

        if (!poolWriter.innerClasses.isEmpty()) {
            writeInnerClasses();
            acount++;
        }

        endAttrs(acountIdx, acount);

        out.write(poolbuf.elems, 0, poolbuf.length);

        poolWriter.writePool(out);
        poolWriter.reset(); // to save space

        out.write(databuf.elems, 0, databuf.length);
    }

     
Allows subclasses to write additional class attributes
Returns:
the number of attributes written/**Allows subclasses to write additional class attributes
      *
      * @return the number of attributes written
      */
    protected int writeExtraClassAttributes(ClassSymbol c) {
        return 0;
    }

    
Allows friends to write additional attributes
Returns:
the number of attributes written/**Allows friends to write additional attributes
     *
     * @return the number of attributes written
     */
    protected int writeExtraAttributes(Symbol sym) {
        int i = 0;
        for (ToIntFunction<Symbol> hook : extraAttributeHooks) {
            i += hook.applyAsInt(sym);
        }
        return i;
    }

    int adjustFlags(final long flags) {
        int result = (int)flags;

        if ((flags & BRIDGE) != 0)
            result |= ACC_BRIDGE;
        if ((flags & VARARGS) != 0)
            result |= ACC_VARARGS;
        if ((flags & DEFAULT) != 0)
            result &= ~ABSTRACT;
        return result;
    }

    long getLastModified(FileObject filename) {
        long mod = 0;
        try {
            mod = filename.getLastModified();
        } catch (SecurityException e) {
            throw new AssertionError("CRT: couldn't get source file modification date: " + e.getMessage());
        }
        return mod;
    }
}