/*
 * Copyright (c) 1999, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.tools.javac.code;

import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.lang.model.element.ElementVisitor;

import com.sun.tools.javac.code.Scope.WriteableScope;
import com.sun.tools.javac.code.Symbol.ClassSymbol;
import com.sun.tools.javac.code.Symbol.Completer;
import com.sun.tools.javac.code.Symbol.CompletionFailure;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.code.Symbol.ModuleSymbol;
import com.sun.tools.javac.code.Symbol.PackageSymbol;
import com.sun.tools.javac.code.Symbol.TypeSymbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.code.Type.BottomType;
import com.sun.tools.javac.code.Type.ClassType;
import com.sun.tools.javac.code.Type.ErrorType;
import com.sun.tools.javac.code.Type.JCPrimitiveType;
import com.sun.tools.javac.code.Type.JCVoidType;
import com.sun.tools.javac.code.Type.MethodType;
import com.sun.tools.javac.code.Type.UnknownType;
import com.sun.tools.javac.comp.Modules;
import com.sun.tools.javac.util.Assert;
import com.sun.tools.javac.util.Context;
import com.sun.tools.javac.util.Convert;
import com.sun.tools.javac.util.DefinedBy;
import com.sun.tools.javac.util.DefinedBy.Api;
import com.sun.tools.javac.util.Iterators;
import com.sun.tools.javac.util.JavacMessages;
import com.sun.tools.javac.util.List;
import com.sun.tools.javac.util.Name;
import com.sun.tools.javac.util.Names;

import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Kinds.Kind.*;
import static com.sun.tools.javac.code.TypeTag.*;

A class that defines all predefined constants and operators
 as well as special classes such as java.lang.Object, which need
 to be known to the compiler. All symbols are held in instance
 fields. This makes it possible to work in multiple concurrent
 projects, which might use different class files for library classes.
 
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.
/** A class that defines all predefined constants and operators
 *  as well as special classes such as java.lang.Object, which need
 *  to be known to the compiler. All symbols are held in instance
 *  fields. This makes it possible to work in multiple concurrent
 *  projects, which might use different class files for library classes.
 *
 *  <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 Symtab {
    
The context key for the symbol table. /** The context key for the symbol table. */
    protected static final Context.Key<Symtab> symtabKey = new Context.Key<>();

    
Get the symbol table instance. /** Get the symbol table instance. */
    public static Symtab instance(Context context) {
        Symtab instance = context.get(symtabKey);
        if (instance == null)
            instance = new Symtab(context);
        return instance;
    }

    
Builtin types.
/** Builtin types.
     */
    public final JCPrimitiveType byteType = new JCPrimitiveType(BYTE, null);
    public final JCPrimitiveType charType = new JCPrimitiveType(CHAR, null);
    public final JCPrimitiveType shortType = new JCPrimitiveType(SHORT, null);
    public final JCPrimitiveType intType = new JCPrimitiveType(INT, null);
    public final JCPrimitiveType longType = new JCPrimitiveType(LONG, null);
    public final JCPrimitiveType floatType = new JCPrimitiveType(FLOAT, null);
    public final JCPrimitiveType doubleType = new JCPrimitiveType(DOUBLE, null);
    public final JCPrimitiveType booleanType = new JCPrimitiveType(BOOLEAN, null);
    public final Type botType = new BottomType();
    public final JCVoidType voidType = new JCVoidType();

    private final Names names;
    private final JavacMessages messages;
    private final Completer initialCompleter;
    private final Completer moduleCompleter;

    
A symbol for the unnamed module.
/** A symbol for the unnamed module.
     */
    public final ModuleSymbol unnamedModule;

    
The error module.
/** The error module.
     */
    public final ModuleSymbol errModule;

    
A symbol for no module, for use with -source 8 or less
/** A symbol for no module, for use with -source 8 or less
     */
    public final ModuleSymbol noModule;

    
A symbol for the root package.
/** A symbol for the root package.
     */
    public final PackageSymbol rootPackage;

    
A symbol that stands for a missing symbol.
/** A symbol that stands for a missing symbol.
     */
    public final TypeSymbol noSymbol;

    
The error symbol.
/** The error symbol.
     */
    public final ClassSymbol errSymbol;

    
The unknown symbol.
/** The unknown symbol.
     */
    public final ClassSymbol unknownSymbol;

    
A value for the errType, with a originalType of noType /** A value for the errType, with a originalType of noType */
    public final Type errType;

    
A value for the unknown type. /** A value for the unknown type. */
    public final Type unknownType;

    
The builtin type of all arrays. /** The builtin type of all arrays. */
    public final ClassSymbol arrayClass;
    public final MethodSymbol arrayCloneMethod;

    
VGJ: The (singleton) type of all bound types. /** VGJ: The (singleton) type of all bound types. */
    public final ClassSymbol boundClass;

    
The builtin type of all methods. /** The builtin type of all methods. */
    public final ClassSymbol methodClass;

    
A symbol for the java.base module.
/** A symbol for the java.base module.
     */
    public final ModuleSymbol java_base;

    
Predefined types.
/** Predefined types.
     */
    public final Type objectType;
    public final Type objectsType;
    public final Type classType;
    public final Type classLoaderType;
    public final Type stringType;
    public final Type stringBufferType;
    public final Type stringBuilderType;
    public final Type cloneableType;
    public final Type serializableType;
    public final Type serializedLambdaType;
    public final Type varHandleType;
    public final Type methodHandleType;
    public final Type methodHandleLookupType;
    public final Type methodTypeType;
    public final Type nativeHeaderType;
    public final Type throwableType;
    public final Type errorType;
    public final Type interruptedExceptionType;
    public final Type illegalArgumentExceptionType;
    public final Type exceptionType;
    public final Type runtimeExceptionType;
    public final Type classNotFoundExceptionType;
    public final Type noClassDefFoundErrorType;
    public final Type noSuchFieldErrorType;
    public final Type assertionErrorType;
    public final Type cloneNotSupportedExceptionType;
    public final Type annotationType;
    public final TypeSymbol enumSym;
    public final Type listType;
    public final Type collectionsType;
    public final Type comparableType;
    public final Type comparatorType;
    public final Type arraysType;
    public final Type iterableType;
    public final Type iteratorType;
    public final Type annotationTargetType;
    public final Type overrideType;
    public final Type retentionType;
    public final Type deprecatedType;
    public final Type suppressWarningsType;
    public final Type supplierType;
    public final Type inheritedType;
    public final Type profileType;
    public final Type proprietaryType;
    public final Type systemType;
    public final Type autoCloseableType;
    public final Type trustMeType;
    public final Type lambdaMetafactory;
    public final Type stringConcatFactory;
    public final Type repeatableType;
    public final Type documentedType;
    public final Type elementTypeType;
    public final Type functionalInterfaceType;

    
The symbol representing the length field of an array.
/** The symbol representing the length field of an array.
     */
    public final VarSymbol lengthVar;

    
The symbol representing the final finalize method on enums /** The symbol representing the final finalize method on enums */
    public final MethodSymbol enumFinalFinalize;

    
The symbol representing the close method on TWR AutoCloseable type /** The symbol representing the close method on TWR AutoCloseable type */
    public final MethodSymbol autoCloseableClose;

    
The predefined type that belongs to a tag.
/** The predefined type that belongs to a tag.
     */
    public final Type[] typeOfTag = new Type[TypeTag.getTypeTagCount()];

    
The name of the class that belongs to a basic type tag.
/** The name of the class that belongs to a basic type tag.
     */
    public final Name[] boxedName = new Name[TypeTag.getTypeTagCount()];

    
A hashtable containing the encountered top-level and member classes,
 indexed by flat names. The table does not contain local classes.
 It should be updated from the outside to reflect classes defined
 by compiled source files.
/** A hashtable containing the encountered top-level and member classes,
     *  indexed by flat names. The table does not contain local classes.
     *  It should be updated from the outside to reflect classes defined
     *  by compiled source files.
     */
    private final Map<Name, Map<ModuleSymbol,ClassSymbol>> classes = new HashMap<>();

    
A hashtable containing the encountered packages.
 the table should be updated from outside to reflect packages defined
 by compiled source files.
/** A hashtable containing the encountered packages.
     *  the table should be updated from outside to reflect packages defined
     *  by compiled source files.
     */
    private final Map<Name, Map<ModuleSymbol,PackageSymbol>> packages = new HashMap<>();

    
A hashtable giving the encountered modules.
/** A hashtable giving the encountered modules.
     */
    private final Map<Name, ModuleSymbol> modules = new LinkedHashMap<>();

    public void initType(Type type, ClassSymbol c) {
        type.tsym = c;
        typeOfTag[type.getTag().ordinal()] = type;
    }

    public void initType(Type type, String name) {
        initType(
            type,
            new ClassSymbol(
                PUBLIC, names.fromString(name), type, rootPackage));
    }

    public void initType(Type type, String name, String bname) {
        initType(type, name);
        boxedName[type.getTag().ordinal()] = names.fromString("java.lang." + bname);
    }

    
The class symbol that owns all predefined symbols.
/** The class symbol that owns all predefined symbols.
     */
    public final ClassSymbol predefClass;

    
Enter a class into symbol table.
 @param s The name of the class.
/** Enter a class into symbol table.
     *  @param s The name of the class.
     */
    private Type enterClass(String s) {
        return enterClass(java_base, names.fromString(s)).type;
    }

    public void synthesizeEmptyInterfaceIfMissing(final Type type) {
        final Completer completer = type.tsym.completer;
        type.tsym.completer = new Completer() {
            @Override
            public void complete(Symbol sym) throws CompletionFailure {
                try {
                    completer.complete(sym);
                } catch (CompletionFailure e) {
                    sym.flags_field |= (PUBLIC | INTERFACE);
                    ((ClassType) sym.type).supertype_field = objectType;
                }
            }

            @Override
            public boolean isTerminal() {
                return completer.isTerminal();
            }
        };
    }

    public void synthesizeBoxTypeIfMissing(final Type type) {
        ClassSymbol sym = enterClass(java_base, boxedName[type.getTag().ordinal()]);
        final Completer completer = sym.completer;
        sym.completer = new Completer() {
            @Override
            public void complete(Symbol sym) throws CompletionFailure {
                try {
                    completer.complete(sym);
                } catch (CompletionFailure e) {
                    sym.flags_field |= PUBLIC;
                    ((ClassType) sym.type).supertype_field = objectType;
                    MethodSymbol boxMethod =
                        new MethodSymbol(PUBLIC | STATIC, names.valueOf,
                                         new MethodType(List.of(type), sym.type,
                                List.nil(), methodClass),
                            sym);
                    sym.members().enter(boxMethod);
                    MethodSymbol unboxMethod =
                        new MethodSymbol(PUBLIC,
                            type.tsym.name.append(names.Value), // x.intValue()
                            new MethodType(List.nil(), type,
                                List.nil(), methodClass),
                            sym);
                    sym.members().enter(unboxMethod);
                }
            }

            @Override
            public boolean isTerminal() {
                return completer.isTerminal();
            }
        };
    }

    // Enter a synthetic class that is used to mark classes in ct.sym.
    // This class does not have a class file.
    private Type enterSyntheticAnnotation(String name) {
        // for now, leave the module null, to prevent problems from synthesizing the
        // existence of a class in any specific module, including noModule
        ClassType type = (ClassType)enterClass(java_base, names.fromString(name)).type;
        ClassSymbol sym = (ClassSymbol)type.tsym;
        sym.completer = Completer.NULL_COMPLETER;
        sym.flags_field = PUBLIC|ACYCLIC|ANNOTATION|INTERFACE;
        sym.erasure_field = type;
        sym.members_field = WriteableScope.create(sym);
        type.typarams_field = List.nil();
        type.allparams_field = List.nil();
        type.supertype_field = annotationType;
        type.interfaces_field = List.nil();
        return type;
    }

    
Constructor; enters all predefined identifiers and operators
 into symbol table.
/** Constructor; enters all predefined identifiers and operators
     *  into symbol table.
     */
    protected Symtab(Context context) throws CompletionFailure {
        context.put(symtabKey, this);

        names = Names.instance(context);

        // Create the unknown type
        unknownType = new UnknownType();

        messages = JavacMessages.instance(context);

        rootPackage = new PackageSymbol(names.empty, null);

        // create the basic builtin symbols
        unnamedModule = new ModuleSymbol(names.empty, null) {
                {
                    directives = List.nil();
                    exports = List.nil();
                    provides = List.nil();
                    uses = List.nil();
                    ModuleSymbol java_base = enterModule(names.java_base);
                    com.sun.tools.javac.code.Directive.RequiresDirective d =
                            new com.sun.tools.javac.code.Directive.RequiresDirective(java_base,
                                    EnumSet.of(com.sun.tools.javac.code.Directive.RequiresFlag.MANDATED));
                    requires = List.of(d);
                }
                @Override
                public String toString() {
                    return messages.getLocalizedString("compiler.misc.unnamed.module");
                }
            };
        addRootPackageFor(unnamedModule);
        unnamedModule.enclosedPackages = unnamedModule.enclosedPackages.prepend(unnamedModule.unnamedPackage);

        errModule = new ModuleSymbol(names.empty, null) {
                {
                    directives = List.nil();
                    exports = List.nil();
                    provides = List.nil();
                    uses = List.nil();
                    ModuleSymbol java_base = enterModule(names.java_base);
                    com.sun.tools.javac.code.Directive.RequiresDirective d =
                            new com.sun.tools.javac.code.Directive.RequiresDirective(java_base,
                                    EnumSet.of(com.sun.tools.javac.code.Directive.RequiresFlag.MANDATED));
                    requires = List.of(d);
                }
            };
        addRootPackageFor(errModule);

        noModule = new ModuleSymbol(names.empty, null) {
            @Override public boolean isNoModule() {
                return true;
            }
        };
        addRootPackageFor(noModule);

        noSymbol = new TypeSymbol(NIL, 0, names.empty, Type.noType, rootPackage) {
            @Override @DefinedBy(Api.LANGUAGE_MODEL)
            public <R, P> R accept(ElementVisitor<R, P> v, P p) {
                return v.visitUnknown(this, p);
            }
        };

        // create the error symbols
        errSymbol = new ClassSymbol(PUBLIC|STATIC|ACYCLIC, names.any, null, rootPackage);
        errType = new ErrorType(errSymbol, Type.noType);

        unknownSymbol = new ClassSymbol(PUBLIC|STATIC|ACYCLIC, names.fromString("<any?>"), null, rootPackage);
        unknownSymbol.members_field = new Scope.ErrorScope(unknownSymbol);
        unknownSymbol.type = unknownType;

        // initialize builtin types
        initType(byteType, "byte", "Byte");
        initType(shortType, "short", "Short");
        initType(charType, "char", "Character");
        initType(intType, "int", "Integer");
        initType(longType, "long", "Long");
        initType(floatType, "float", "Float");
        initType(doubleType, "double", "Double");
        initType(booleanType, "boolean", "Boolean");
        initType(voidType, "void", "Void");
        initType(botType, "<nulltype>");
        initType(errType, errSymbol);
        initType(unknownType, unknownSymbol);

        // the builtin class of all arrays
        arrayClass = new ClassSymbol(PUBLIC|ACYCLIC, names.Array, noSymbol);

        // VGJ
        boundClass = new ClassSymbol(PUBLIC|ACYCLIC, names.Bound, noSymbol);
        boundClass.members_field = new Scope.ErrorScope(boundClass);

        // the builtin class of all methods
        methodClass = new ClassSymbol(PUBLIC|ACYCLIC, names.Method, noSymbol);
        methodClass.members_field = new Scope.ErrorScope(boundClass);

        // Create class to hold all predefined constants and operations.
        predefClass = new ClassSymbol(PUBLIC|ACYCLIC, names.empty, rootPackage);
        WriteableScope scope = WriteableScope.create(predefClass);
        predefClass.members_field = scope;

        // Get the initial completer for Symbols from the ClassFinder
        initialCompleter = ClassFinder.instance(context).getCompleter();
        rootPackage.members_field = WriteableScope.create(rootPackage);

        // Enter symbols for basic types.
        scope.enter(byteType.tsym);
        scope.enter(shortType.tsym);
        scope.enter(charType.tsym);
        scope.enter(intType.tsym);
        scope.enter(longType.tsym);
        scope.enter(floatType.tsym);
        scope.enter(doubleType.tsym);
        scope.enter(booleanType.tsym);
        scope.enter(errType.tsym);

        // Enter symbol for the errSymbol
        scope.enter(errSymbol);

        Source source = Source.instance(context);
        if (source.allowModules()) {
            java_base = enterModule(names.java_base);
            //avoid completing java.base during the Symtab initialization
            java_base.completer = Completer.NULL_COMPLETER;
            java_base.visiblePackages = Collections.emptyMap();
        } else {
            java_base = noModule;
        }

        // Get the initial completer for ModuleSymbols from Modules
        moduleCompleter = Modules.instance(context).getCompleter();

        // Enter predefined classes. All are assumed to be in the java.base module.
        objectType = enterClass("java.lang.Object");
        objectsType = enterClass("java.util.Objects");
        classType = enterClass("java.lang.Class");
        stringType = enterClass("java.lang.String");
        stringBufferType = enterClass("java.lang.StringBuffer");
        stringBuilderType = enterClass("java.lang.StringBuilder");
        cloneableType = enterClass("java.lang.Cloneable");
        throwableType = enterClass("java.lang.Throwable");
        serializableType = enterClass("java.io.Serializable");
        serializedLambdaType = enterClass("java.lang.invoke.SerializedLambda");
        varHandleType = enterClass("java.lang.invoke.VarHandle");
        methodHandleType = enterClass("java.lang.invoke.MethodHandle");
        methodHandleLookupType = enterClass("java.lang.invoke.MethodHandles$Lookup");
        methodTypeType = enterClass("java.lang.invoke.MethodType");
        errorType = enterClass("java.lang.Error");
        illegalArgumentExceptionType = enterClass("java.lang.IllegalArgumentException");
        interruptedExceptionType = enterClass("java.lang.InterruptedException");
        exceptionType = enterClass("java.lang.Exception");
        runtimeExceptionType = enterClass("java.lang.RuntimeException");
        classNotFoundExceptionType = enterClass("java.lang.ClassNotFoundException");
        noClassDefFoundErrorType = enterClass("java.lang.NoClassDefFoundError");
        noSuchFieldErrorType = enterClass("java.lang.NoSuchFieldError");
        assertionErrorType = enterClass("java.lang.AssertionError");
        cloneNotSupportedExceptionType = enterClass("java.lang.CloneNotSupportedException");
        annotationType = enterClass("java.lang.annotation.Annotation");
        classLoaderType = enterClass("java.lang.ClassLoader");
        enumSym = enterClass(java_base, names.java_lang_Enum);
        enumFinalFinalize =
            new MethodSymbol(PROTECTED|FINAL|HYPOTHETICAL,
                             names.finalize,
                             new MethodType(List.nil(), voidType,
                                            List.nil(), methodClass),
                             enumSym);
        listType = enterClass("java.util.List");
        collectionsType = enterClass("java.util.Collections");
        comparableType = enterClass("java.lang.Comparable");
        comparatorType = enterClass("java.util.Comparator");
        arraysType = enterClass("java.util.Arrays");
        iterableType = enterClass("java.lang.Iterable");
        iteratorType = enterClass("java.util.Iterator");
        annotationTargetType = enterClass("java.lang.annotation.Target");
        overrideType = enterClass("java.lang.Override");
        retentionType = enterClass("java.lang.annotation.Retention");
        deprecatedType = enterClass("java.lang.Deprecated");
        suppressWarningsType = enterClass("java.lang.SuppressWarnings");
        supplierType = enterClass("java.util.function.Supplier");
        inheritedType = enterClass("java.lang.annotation.Inherited");
        repeatableType = enterClass("java.lang.annotation.Repeatable");
        documentedType = enterClass("java.lang.annotation.Documented");
        elementTypeType = enterClass("java.lang.annotation.ElementType");
        systemType = enterClass("java.lang.System");
        autoCloseableType = enterClass("java.lang.AutoCloseable");
        autoCloseableClose = new MethodSymbol(PUBLIC,
                             names.close,
                             new MethodType(List.nil(), voidType,
                                            List.of(exceptionType), methodClass),
                             autoCloseableType.tsym);
        trustMeType = enterClass("java.lang.SafeVarargs");
        nativeHeaderType = enterClass("java.lang.annotation.Native");
        lambdaMetafactory = enterClass("java.lang.invoke.LambdaMetafactory");
        stringConcatFactory = enterClass("java.lang.invoke.StringConcatFactory");
        functionalInterfaceType = enterClass("java.lang.FunctionalInterface");

        synthesizeEmptyInterfaceIfMissing(autoCloseableType);
        synthesizeEmptyInterfaceIfMissing(cloneableType);
        synthesizeEmptyInterfaceIfMissing(serializableType);
        synthesizeEmptyInterfaceIfMissing(lambdaMetafactory);
        synthesizeEmptyInterfaceIfMissing(serializedLambdaType);
        synthesizeEmptyInterfaceIfMissing(stringConcatFactory);
        synthesizeBoxTypeIfMissing(doubleType);
        synthesizeBoxTypeIfMissing(floatType);
        synthesizeBoxTypeIfMissing(voidType);

        // Enter a synthetic class that is used to mark internal
        // proprietary classes in ct.sym.  This class does not have a
        // class file.
        proprietaryType = enterSyntheticAnnotation("sun.Proprietary+Annotation");

        // Enter a synthetic class that is used to provide profile info for
        // classes in ct.sym.  This class does not have a class file.
        profileType = enterSyntheticAnnotation("jdk.Profile+Annotation");
        MethodSymbol m = new MethodSymbol(PUBLIC | ABSTRACT, names.value, intType, profileType.tsym);
        profileType.tsym.members().enter(m);

        // Enter a class for arrays.
        // The class implements java.lang.Cloneable and java.io.Serializable.
        // It has a final length field and a clone method.
        ClassType arrayClassType = (ClassType)arrayClass.type;
        arrayClassType.supertype_field = objectType;
        arrayClassType.interfaces_field = List.of(cloneableType, serializableType);
        arrayClass.members_field = WriteableScope.create(arrayClass);
        lengthVar = new VarSymbol(
            PUBLIC | FINAL,
            names.length,
            intType,
            arrayClass);
        arrayClass.members().enter(lengthVar);
        arrayCloneMethod = new MethodSymbol(
            PUBLIC,
            names.clone,
            new MethodType(List.nil(), objectType,
                           List.nil(), methodClass),
            arrayClass);
        arrayClass.members().enter(arrayCloneMethod);

        if (java_base != noModule)
            java_base.completer = moduleCompleter::complete; //bootstrap issues

    }

    
Define a new class given its name and owner.
/** Define a new class given its name and owner.
     */
    public ClassSymbol defineClass(Name name, Symbol owner) {
        ClassSymbol c = new ClassSymbol(0, name, owner);
        c.completer = initialCompleter;
        return c;
    }

    
Create a new toplevel or member class symbol with given name
 and owner and enter in `classes' unless already there.
/** Create a new toplevel or member class symbol with given name
     *  and owner and enter in `classes' unless already there.
     */
    public ClassSymbol enterClass(ModuleSymbol msym, Name name, TypeSymbol owner) {
        Assert.checkNonNull(msym);
        Name flatname = TypeSymbol.formFlatName(name, owner);
        ClassSymbol c = getClass(msym, flatname);
        if (c == null) {
            c = defineClass(name, owner);
            doEnterClass(msym, c);
        } else if ((c.name != name || c.owner != owner) && owner.kind == TYP && c.owner.kind == PCK) {
            // reassign fields of classes that might have been loaded with
            // their flat names.
            c.owner.members().remove(c);
            c.name = name;
            c.owner = owner;
            c.fullname = ClassSymbol.formFullName(name, owner);
        }
        return c;
    }

    public ClassSymbol getClass(ModuleSymbol msym, Name flatName) {
        Assert.checkNonNull(msym, flatName::toString);
        return classes.getOrDefault(flatName, Collections.emptyMap()).get(msym);
    }

    public PackageSymbol lookupPackage(ModuleSymbol msym, Name flatName) {
        Assert.checkNonNull(msym);

        if (flatName.isEmpty()) {
            //unnamed packages only from the current module - visiblePackages contains *root* package, not unnamed package!
            return msym.unnamedPackage;
        }

        if (msym == noModule) {
            return enterPackage(msym, flatName);
        }

        msym.complete();

        PackageSymbol pack;

        pack = msym.visiblePackages.get(flatName);

        if (pack != null)
            return pack;

        pack = getPackage(msym, flatName);

        if (pack != null && pack.exists())
            return pack;

        boolean dependsOnUnnamed = msym.requires != null &&
                                   msym.requires.stream()
                                                .map(rd -> rd.module)
                                                .anyMatch(mod -> mod == unnamedModule);

        if (dependsOnUnnamed) {
            //msyms depends on the unnamed module, for which we generally don't know
            //the list of packages it "exports" ahead of time. So try to lookup the package in the
            //current module, and in the unnamed module and see if it exists in one of them
            PackageSymbol unnamedPack = getPackage(unnamedModule, flatName);

            if (unnamedPack != null && unnamedPack.exists()) {
                msym.visiblePackages.put(unnamedPack.fullname, unnamedPack);
                return unnamedPack;
            }

            pack = enterPackage(msym, flatName);
            pack.complete();
            if (pack.exists())
                return pack;

            unnamedPack = enterPackage(unnamedModule, flatName);
            unnamedPack.complete();
            if (unnamedPack.exists()) {
                msym.visiblePackages.put(unnamedPack.fullname, unnamedPack);
                return unnamedPack;
            }

            return pack;
        }

        return enterPackage(msym, flatName);
    }

    private static final Map<ModuleSymbol, ClassSymbol> EMPTY = new HashMap<>();

    public void removeClass(ModuleSymbol msym, Name flatName) {
        classes.getOrDefault(flatName, EMPTY).remove(msym);
    }

    public Iterable<ClassSymbol> getAllClasses() {
        return () -> Iterators.createCompoundIterator(classes.values(), v -> v.values().iterator());
    }

    private void doEnterClass(ModuleSymbol msym, ClassSymbol cs) {
        classes.computeIfAbsent(cs.flatname, n -> new HashMap<>()).put(msym, cs);
    }

    
Create a new member or toplevel class symbol with given flat name
 and enter in `classes' unless already there.
/** Create a new member or toplevel class symbol with given flat name
     *  and enter in `classes' unless already there.
     */
    public ClassSymbol enterClass(ModuleSymbol msym, Name flatname) {
        Assert.checkNonNull(msym);
        PackageSymbol ps = lookupPackage(msym, Convert.packagePart(flatname));
        Assert.checkNonNull(ps);
        Assert.checkNonNull(ps.modle);
        ClassSymbol c = getClass(ps.modle, flatname);
        if (c == null) {
            c = defineClass(Convert.shortName(flatname), ps);
            doEnterClass(ps.modle, c);
            return c;
        } else
            return c;
    }

    
Check to see if a package exists, given its fully qualified name.
/** Check to see if a package exists, given its fully qualified name.
     */
    public boolean packageExists(ModuleSymbol msym, Name fullname) {
        Assert.checkNonNull(msym);
        return lookupPackage(msym, fullname).exists();
    }

    
Make a package, given its fully qualified name.
/** Make a package, given its fully qualified name.
     */
    public PackageSymbol enterPackage(ModuleSymbol currModule, Name fullname) {
        Assert.checkNonNull(currModule);
        PackageSymbol p = getPackage(currModule, fullname);
        if (p == null) {
            Assert.check(!fullname.isEmpty(), () -> "rootPackage missing!; currModule: " + currModule);
            p = new PackageSymbol(
                    Convert.shortName(fullname),
                    enterPackage(currModule, Convert.packagePart(fullname)));
            p.completer = initialCompleter;
            p.modle = currModule;
            doEnterPackage(currModule, p);
        }
        return p;
    }

    private void doEnterPackage(ModuleSymbol msym, PackageSymbol pack) {
        packages.computeIfAbsent(pack.fullname, n -> new HashMap<>()).put(msym, pack);
        msym.enclosedPackages = msym.enclosedPackages.prepend(pack);
    }

    private void addRootPackageFor(ModuleSymbol module) {
        doEnterPackage(module, rootPackage);
        PackageSymbol unnamedPackage = new PackageSymbol(names.empty, rootPackage) {
                @Override
                public String toString() {
                    return messages.getLocalizedString("compiler.misc.unnamed.package");
                }
            };
        unnamedPackage.modle = module;
        //we cannot use a method reference below, as initialCompleter might be null now
        unnamedPackage.completer = s -> initialCompleter.complete(s);
        module.unnamedPackage = unnamedPackage;
    }

    public PackageSymbol getPackage(ModuleSymbol module, Name fullname) {
        return packages.getOrDefault(fullname, Collections.emptyMap()).get(module);
    }

    public ModuleSymbol enterModule(Name name) {
        ModuleSymbol msym = modules.get(name);
        if (msym == null) {
            msym = ModuleSymbol.create(name, names.module_info);
            addRootPackageFor(msym);
            msym.completer = s -> moduleCompleter.complete(s); //bootstrap issues
            modules.put(name, msym);
        }
        return msym;
    }

    public ModuleSymbol getModule(Name name) {
        return modules.get(name);
    }

    //temporary:
    public ModuleSymbol inferModule(Name packageName) {
        if (packageName.isEmpty())
            return java_base == noModule ? noModule : unnamedModule;//!

        ModuleSymbol msym = null;
        Map<ModuleSymbol,PackageSymbol> map = packages.get(packageName);
        if (map == null)
            return null;
        for (Map.Entry<ModuleSymbol,PackageSymbol> e: map.entrySet()) {
            if (!e.getValue().members().isEmpty()) {
                if (msym == null) {
                    msym = e.getKey();
                } else {
                    return null;
                }
            }
        }
        return msym;
    }

    public List<ModuleSymbol> listPackageModules(Name packageName) {
        if (packageName.isEmpty())
            return List.nil();

        List<ModuleSymbol> result = List.nil();
        Map<ModuleSymbol,PackageSymbol> map = packages.get(packageName);
        if (map != null) {
            for (Map.Entry<ModuleSymbol, PackageSymbol> e: map.entrySet()) {
                if (!e.getValue().members().isEmpty()) {
                    result = result.prepend(e.getKey());
                }
            }
        }
        return result;
    }

    public Collection<ModuleSymbol> getAllModules() {
        return modules.values();
    }

    public Iterable<ClassSymbol> getClassesForName(Name candidate) {
        return classes.getOrDefault(candidate, Collections.emptyMap()).values();
    }

    public Iterable<PackageSymbol> getPackagesForName(Name candidate) {
        return packages.getOrDefault(candidate, Collections.emptyMap()).values();
    }
}