/*
 * Copyright (c) 2003, 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.file;

import java.io.Closeable;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import java.net.URI;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.DirectoryIteratorException;
import java.nio.file.DirectoryStream;
import java.nio.file.FileSystem;
import java.nio.file.FileSystemNotFoundException;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.InvalidPathException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.ProviderNotFoundException;
import java.nio.file.spi.FileSystemProvider;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumMap;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.function.Predicate;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.util.jar.Attributes;
import java.util.jar.Manifest;

import javax.lang.model.SourceVersion;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileManager.Location;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardJavaFileManager.PathFactory;
import javax.tools.StandardLocation;

import com.sun.tools.javac.code.Lint;
import com.sun.tools.javac.code.Lint.LintCategory;
import com.sun.tools.javac.main.Option;
import com.sun.tools.javac.resources.CompilerProperties.Errors;
import com.sun.tools.javac.resources.CompilerProperties.Warnings;
import com.sun.tools.javac.util.DefinedBy;
import com.sun.tools.javac.util.DefinedBy.Api;
import com.sun.tools.javac.util.JDK9Wrappers;
import com.sun.tools.javac.util.ListBuffer;
import com.sun.tools.javac.util.Log;
import com.sun.tools.javac.jvm.ModuleNameReader;
import com.sun.tools.javac.util.Assert;
import com.sun.tools.javac.util.Pair;
import com.sun.tools.javac.util.StringUtils;

import static javax.tools.StandardLocation.PLATFORM_CLASS_PATH;

import static com.sun.tools.javac.main.Option.BOOT_CLASS_PATH;
import static com.sun.tools.javac.main.Option.DJAVA_ENDORSED_DIRS;
import static com.sun.tools.javac.main.Option.DJAVA_EXT_DIRS;
import static com.sun.tools.javac.main.Option.ENDORSEDDIRS;
import static com.sun.tools.javac.main.Option.EXTDIRS;
import static com.sun.tools.javac.main.Option.XBOOTCLASSPATH;
import static com.sun.tools.javac.main.Option.XBOOTCLASSPATH_APPEND;
import static com.sun.tools.javac.main.Option.XBOOTCLASSPATH_PREPEND;

This class converts command line arguments, environment variables and system properties (in File.pathSeparator-separated String form) into a boot class path, user class path, and source path (in Collection<String> form). 

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 converts command line arguments, environment variables and system properties (in
 * File.pathSeparator-separated String form) into a boot class path, user class path, and source
 * path (in {@code Collection<String>} form).
 *
 * <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 Locations {

    
The log to use for warning output
/**
     * The log to use for warning output
     */
    private Log log;

    
Access to (possibly cached) file info
/**
     * Access to (possibly cached) file info
     */
    private FSInfo fsInfo;

    
Whether to warn about non-existent path elements
/**
     * Whether to warn about non-existent path elements
     */
    private boolean warn;

    private ModuleNameReader moduleNameReader;

    private PathFactory pathFactory = Paths::get;

    static final Path javaHome = FileSystems.getDefault().getPath(System.getProperty("java.home"));
    static final Path thisSystemModules = javaHome.resolve("lib").resolve("modules");

    Map<Path, FileSystem> fileSystems = new LinkedHashMap<>();
    List<Closeable> closeables = new ArrayList<>();
    private Map<String,String> fsEnv = Collections.emptyMap();

    Locations() {
        initHandlers();
    }

    Path getPath(String first, String... more) {
        try {
            return pathFactory.getPath(first, more);
        } catch (InvalidPathException ipe) {
            throw new IllegalArgumentException(ipe);
        }
    }

    public void close() throws IOException {
        ListBuffer<IOException> list = new ListBuffer<>();
        closeables.forEach(closeable -> {
            try {
                closeable.close();
            } catch (IOException ex) {
                list.add(ex);
            }
        });
        if (list.nonEmpty()) {
            IOException ex = new IOException();
            for (IOException e: list)
                ex.addSuppressed(e);
            throw ex;
        }
    }

    void update(Log log, boolean warn, FSInfo fsInfo) {
        this.log = log;
        this.warn = warn;
        this.fsInfo = fsInfo;
    }

    void setPathFactory(PathFactory f) {
        pathFactory = f;
    }

    boolean isDefaultBootClassPath() {
        BootClassPathLocationHandler h
                = (BootClassPathLocationHandler) getHandler(PLATFORM_CLASS_PATH);
        return h.isDefault();
    }

    
Split a search path into its elements. Empty path elements will be ignored.
Params:
searchPath – The search path to be split
Returns:
The elements of the path/**
     * Split a search path into its elements. Empty path elements will be ignored.
     *
     * @param searchPath The search path to be split
     * @return The elements of the path
     */
    private Iterable<Path> getPathEntries(String searchPath) {
        return getPathEntries(searchPath, null);
    }

    
Split a search path into its elements. If emptyPathDefault is not null, all empty elements in the
path, including empty elements at either end of the path, will be replaced with the value of
emptyPathDefault.
Params:
searchPath – The search path to be split
emptyPathDefault – The value to substitute for empty path elements, or null, to ignore
empty path elements
Returns:
The elements of the path/**
     * Split a search path into its elements. If emptyPathDefault is not null, all empty elements in the
     * path, including empty elements at either end of the path, will be replaced with the value of
     * emptyPathDefault.
     *
     * @param searchPath The search path to be split
     * @param emptyPathDefault The value to substitute for empty path elements, or null, to ignore
     * empty path elements
     * @return The elements of the path
     */
    private Iterable<Path> getPathEntries(String searchPath, Path emptyPathDefault) {
        ListBuffer<Path> entries = new ListBuffer<>();
        for (String s: searchPath.split(Pattern.quote(File.pathSeparator), -1)) {
            if (s.isEmpty()) {
                if (emptyPathDefault != null) {
                    entries.add(emptyPathDefault);
                }
            } else {
                try {
                    entries.add(getPath(s));
                } catch (IllegalArgumentException e) {
                    if (warn) {
                        log.warning(LintCategory.PATH, "invalid.path", s);
                    }
                }
            }
        }
        return entries;
    }

    public void setMultiReleaseValue(String multiReleaseValue) {
        fsEnv = Collections.singletonMap("multi-release", multiReleaseValue);
    }

    private boolean contains(Collection<Path> searchPath, Path file) throws IOException {

        if (searchPath == null) {
            return false;
        }

        Path enclosingJar = null;
        if (file.getFileSystem().provider() == fsInfo.getJarFSProvider()) {
            URI uri = file.toUri();
            if (uri.getScheme().equals("jar")) {
                String ssp = uri.getSchemeSpecificPart();
                int sep = ssp.lastIndexOf("!");
                if (ssp.startsWith("file:") && sep > 0) {
                    enclosingJar = Paths.get(URI.create(ssp.substring(0, sep)));
                }
            }
        }

        Path nf = normalize(file);
        for (Path p : searchPath) {
            Path np = normalize(p);
            if (np.getFileSystem() == nf.getFileSystem()
                    && Files.isDirectory(np)
                    && nf.startsWith(np)) {
                return true;
            }
            if (enclosingJar != null
                    && Files.isSameFile(enclosingJar, np)) {
                return true;
            }
        }

        return false;
    }

    
Utility class to help evaluate a path option. Duplicate entries are ignored, jar class paths
can be expanded.
/**
     * Utility class to help evaluate a path option. Duplicate entries are ignored, jar class paths
     * can be expanded.
     */
    private class SearchPath extends LinkedHashSet<Path> {

        private static final long serialVersionUID = 0;

        private boolean expandJarClassPaths = false;
        private final Set<Path> canonicalValues = new HashSet<>();

        public SearchPath expandJarClassPaths(boolean x) {
            expandJarClassPaths = x;
            return this;
        }

        
What to use when path element is the empty string
/**
         * What to use when path element is the empty string
         */
        private Path emptyPathDefault = null;

        public SearchPath emptyPathDefault(Path x) {
            emptyPathDefault = x;
            return this;
        }

        public SearchPath addDirectories(String dirs, boolean warn) {
            boolean prev = expandJarClassPaths;
            expandJarClassPaths = true;
            try {
                if (dirs != null) {
                    for (Path dir : getPathEntries(dirs)) {
                        addDirectory(dir, warn);
                    }
                }
                return this;
            } finally {
                expandJarClassPaths = prev;
            }
        }

        public SearchPath addDirectories(String dirs) {
            return addDirectories(dirs, warn);
        }

        private void addDirectory(Path dir, boolean warn) {
            if (!Files.isDirectory(dir)) {
                if (warn) {
                    log.warning(Lint.LintCategory.PATH,
                            "dir.path.element.not.found", dir);
                }
                return;
            }

            try (Stream<Path> s = Files.list(dir)) {
                s.filter(Locations.this::isArchive)
                        .forEach(dirEntry -> addFile(dirEntry, warn));
            } catch (IOException ignore) {
            }
        }

        public SearchPath addFiles(String files, boolean warn) {
            if (files != null) {
                addFiles(getPathEntries(files, emptyPathDefault), warn);
            }
            return this;
        }

        public SearchPath addFiles(String files) {
            return addFiles(files, warn);
        }

        public SearchPath addFiles(Iterable<? extends Path> files, boolean warn) {
            if (files != null) {
                for (Path file : files) {
                    addFile(file, warn);
                }
            }
            return this;
        }

        public SearchPath addFiles(Iterable<? extends Path> files) {
            return addFiles(files, warn);
        }

        public void addFile(Path file, boolean warn) {
            if (contains(file)) {
                // discard duplicates
                return;
            }

            if (!fsInfo.exists(file)) {
                /* No such file or directory exists */
                if (warn) {
                    log.warning(Lint.LintCategory.PATH,
                            "path.element.not.found", file);
                }
                super.add(file);
                return;
            }

            Path canonFile = fsInfo.getCanonicalFile(file);
            if (canonicalValues.contains(canonFile)) {
                /* Discard duplicates and avoid infinite recursion */
                return;
            }

            if (fsInfo.isFile(file)) {
                /* File is an ordinary file. */
                if (   !file.getFileName().toString().endsWith(".jmod")
                    && !file.endsWith("modules")) {
                    if (!isArchive(file)) {
                        /* Not a recognized extension; open it to see if
                         it looks like a valid zip file. */
                        try {
                            FileSystems.newFileSystem(file, null).close();
                            if (warn) {
                                log.warning(Lint.LintCategory.PATH,
                                        "unexpected.archive.file", file);
                            }
                        } catch (IOException | ProviderNotFoundException e) {
                            // FIXME: include e.getLocalizedMessage in warning
                            if (warn) {
                                log.warning(Lint.LintCategory.PATH,
                                        "invalid.archive.file", file);
                            }
                            return;
                        }
                    } else {
                        if (fsInfo.getJarFSProvider() == null) {
                            log.error(Errors.NoZipfsForArchive(file));
                            return ;
                        }
                    }
                }
            }

            /* Now what we have left is either a directory or a file name
             conforming to archive naming convention */
            super.add(file);
            canonicalValues.add(canonFile);

            if (expandJarClassPaths && fsInfo.isFile(file) && !file.endsWith("modules")) {
                addJarClassPath(file, warn);
            }
        }

        // Adds referenced classpath elements from a jar's Class-Path
        // Manifest entry.  In some future release, we may want to
        // update this code to recognize URLs rather than simple
        // filenames, but if we do, we should redo all path-related code.
        private void addJarClassPath(Path jarFile, boolean warn) {
            try {
                for (Path f : fsInfo.getJarClassPath(jarFile)) {
                    addFile(f, warn);
                }
            } catch (IOException e) {
                log.error("error.reading.file", jarFile, JavacFileManager.getMessage(e));
            }
        }
    }

    
Base class for handling support for the representation of Locations.
Locations are (by design) opaque handles that can easily be implemented
by enums like StandardLocation. Within JavacFileManager, each Location
has an associated LocationHandler, which provides much of the appropriate
functionality for the corresponding Location.
See Also:
initHandlers
getHandler/**
     * Base class for handling support for the representation of Locations.
     *
     * Locations are (by design) opaque handles that can easily be implemented
     * by enums like StandardLocation. Within JavacFileManager, each Location
     * has an associated LocationHandler, which provides much of the appropriate
     * functionality for the corresponding Location.
     *
     * @see #initHandlers
     * @see #getHandler
     */
    protected static abstract class LocationHandler {

        
See Also:
handleOption.handleOption/**
         * @see JavaFileManager#handleOption
         */
        abstract boolean handleOption(Option option, String value);

        
See Also:
hasLocation.hasLocation/**
         * @see StandardJavaFileManager#hasLocation
         */
        boolean isSet() {
            return (getPaths() != null);
        }

        
See Also:
getLocation.getLocation/**
         * @see StandardJavaFileManager#getLocation
         */
        abstract Collection<Path> getPaths();

        
See Also:
setLocation.setLocation/**
         * @see StandardJavaFileManager#setLocation
         */
        abstract void setPaths(Iterable<? extends Path> paths) throws IOException;

        
See Also:
setLocationForModule.setLocationForModule/**
         * @see StandardJavaFileManager#setLocationForModule
         */
        abstract void setPathsForModule(String moduleName, Iterable<? extends Path> paths)
                throws IOException;

        
See Also:
getLocationForModule.getLocationForModule(Location, String)/**
         * @see JavaFileManager#getLocationForModule(Location, String)
         */
        Location getLocationForModule(String moduleName) throws IOException {
            return null;
        }

        
See Also:
getLocationForModule.getLocationForModule(Location, JavaFileObject, String)/**
         * @see JavaFileManager#getLocationForModule(Location, JavaFileObject, String)
         */
        Location getLocationForModule(Path file) throws IOException  {
            return null;
        }

        
See Also:
inferModuleName.inferModuleName/**
         * @see JavaFileManager#inferModuleName
         */
        String inferModuleName() {
            return null;
        }

        
See Also:
listLocationsForModules.listLocationsForModules/**
         * @see JavaFileManager#listLocationsForModules
         */
        Iterable<Set<Location>> listLocationsForModules() throws IOException {
            return null;
        }

        
See Also:
contains.contains/**
         * @see JavaFileManager#contains
         */
        abstract boolean contains(Path file) throws IOException;
    }

    
A LocationHandler for a given Location, and associated set of options.
/**
     * A LocationHandler for a given Location, and associated set of options.
     */
    private static abstract class BasicLocationHandler extends LocationHandler {

        final Location location;
        final Set<Option> options;

        
Create a handler. The location and options provide a way to map from a location or an
option to the corresponding handler.
Params:
location – the location for which this is the handler
options – the options affecting this location
See Also:
initHandlers/**
         * Create a handler. The location and options provide a way to map from a location or an
         * option to the corresponding handler.
         *
         * @param location the location for which this is the handler
         * @param options the options affecting this location
         * @see #initHandlers
         */
        protected BasicLocationHandler(Location location, Option... options) {
            this.location = location;
            this.options = options.length == 0
                    ? EnumSet.noneOf(Option.class)
                    : EnumSet.copyOf(Arrays.asList(options));
        }

        @Override
        void setPathsForModule(String moduleName, Iterable<? extends Path> files) throws IOException {
            // should not happen: protected by check in JavacFileManager
            throw new UnsupportedOperationException("not supported for " + location);
        }

        protected Path checkSingletonDirectory(Iterable<? extends Path> paths) throws IOException {
            Iterator<? extends Path> pathIter = paths.iterator();
            if (!pathIter.hasNext()) {
                throw new IllegalArgumentException("empty path for directory");
            }
            Path path = pathIter.next();
            if (pathIter.hasNext()) {
                throw new IllegalArgumentException("path too long for directory");
            }
            checkDirectory(path);
            return path;
        }

        protected Path checkDirectory(Path path) throws IOException {
            Objects.requireNonNull(path);
            if (!Files.exists(path)) {
                throw new FileNotFoundException(path + ": does not exist");
            }
            if (!Files.isDirectory(path)) {
                throw new IOException(path + ": not a directory");
            }
            return path;
        }
    }

    
General purpose implementation for output locations, such as -d/CLASS_OUTPUT and
-s/SOURCE_OUTPUT. All options are treated as equivalent (i.e. aliases.)
The value is a single file, possibly null.
/**
     * General purpose implementation for output locations, such as -d/CLASS_OUTPUT and
     * -s/SOURCE_OUTPUT. All options are treated as equivalent (i.e. aliases.)
     * The value is a single file, possibly null.
     */
    private class OutputLocationHandler extends BasicLocationHandler {

        private Path outputDir;
        private ModuleTable moduleTable;

        OutputLocationHandler(Location location, Option... options) {
            super(location, options);
        }

        @Override
        boolean handleOption(Option option, String value) {
            if (!options.contains(option)) {
                return false;
            }

            // TODO: could/should validate outputDir exists and is a directory
            // need to decide how best to report issue for benefit of
            // direct API call on JavaFileManager.handleOption(specifies IAE)
            // vs. command line decoding.
            outputDir = (value == null) ? null : getPath(value);
            return true;
        }

        @Override
        Collection<Path> getPaths() {
            return (outputDir == null) ? null : Collections.singleton(outputDir);
        }

        @Override
        void setPaths(Iterable<? extends Path> paths) throws IOException {
            if (paths == null) {
                outputDir = null;
            } else {
                outputDir = checkSingletonDirectory(paths);
            }
            moduleTable = null;
            listed = false;
        }

        @Override
        Location getLocationForModule(String name) {
            if (moduleTable == null) {
                moduleTable = new ModuleTable();
            }
            ModuleLocationHandler l = moduleTable.get(name);
            if (l == null) {
                Path out = outputDir.resolve(name);
                l = new ModuleLocationHandler(this, location.getName() + "[" + name + "]",
                        name, Collections.singletonList(out), true);
                moduleTable.add(l);
            }
            return l;
        }

        @Override
        void setPathsForModule(String name, Iterable<? extends Path> paths) throws IOException {
            Path out = checkSingletonDirectory(paths);
            if (moduleTable == null) {
                moduleTable = new ModuleTable();
            }
            ModuleLocationHandler l = moduleTable.get(name);
            if (l == null) {
                l = new ModuleLocationHandler(this, location.getName() + "[" + name + "]",
                        name, Collections.singletonList(out), true);
                moduleTable.add(l);
           } else {
                l.searchPath = Collections.singletonList(out);
                moduleTable.updatePaths(l);
            }
        }

        @Override
        Location getLocationForModule(Path file) {
            return (moduleTable == null) ? null : moduleTable.get(file);
        }

        private boolean listed;

        @Override
        Iterable<Set<Location>> listLocationsForModules() throws IOException {
            if (!listed && outputDir != null) {
                try (DirectoryStream<Path> stream = Files.newDirectoryStream(outputDir)) {
                    for (Path p : stream) {
                        getLocationForModule(p.getFileName().toString());
                    }
                }
                listed = true;
            }

            if (moduleTable == null || moduleTable.isEmpty())
                return Collections.emptySet();

            return Collections.singleton(moduleTable.locations());
        }

        @Override
        boolean contains(Path file) throws IOException {
            if (moduleTable != null) {
                return moduleTable.contains(file);
            } else {
                return (outputDir) != null && normalize(file).startsWith(normalize(outputDir));
            }
        }
    }

    
General purpose implementation for search path locations,
such as -sourcepath/SOURCE_PATH and -processorPath/ANNOTATION_PROCESSOR_PATH.
All options are treated as equivalent (i.e. aliases.)
The value is an ordered set of files and/or directories.
/**
     * General purpose implementation for search path locations,
     * such as -sourcepath/SOURCE_PATH and -processorPath/ANNOTATION_PROCESSOR_PATH.
     * All options are treated as equivalent (i.e. aliases.)
     * The value is an ordered set of files and/or directories.
     */
    private class SimpleLocationHandler extends BasicLocationHandler {

        protected Collection<Path> searchPath;

        SimpleLocationHandler(Location location, Option... options) {
            super(location, options);
        }

        @Override
        boolean handleOption(Option option, String value) {
            if (!options.contains(option)) {
                return false;
            }
            searchPath = value == null ? null
                    : Collections.unmodifiableCollection(createPath().addFiles(value));
            return true;
        }

        @Override
        Collection<Path> getPaths() {
            return searchPath;
        }

        @Override
        void setPaths(Iterable<? extends Path> files) {
            SearchPath p;
            if (files == null) {
                p = computePath(null);
            } else {
                p = createPath().addFiles(files);
            }
            searchPath = Collections.unmodifiableCollection(p);
        }

        protected SearchPath computePath(String value) {
            return createPath().addFiles(value);
        }

        protected SearchPath createPath() {
            return new SearchPath();
        }

        @Override
        boolean contains(Path file) throws IOException {
            return Locations.this.contains(searchPath, file);
        }
    }

    
Subtype of SimpleLocationHandler for -classpath/CLASS_PATH.
If no value is given, a default is provided, based on system properties and other values.
/**
     * Subtype of SimpleLocationHandler for -classpath/CLASS_PATH.
     * If no value is given, a default is provided, based on system properties and other values.
     */
    private class ClassPathLocationHandler extends SimpleLocationHandler {

        ClassPathLocationHandler() {
            super(StandardLocation.CLASS_PATH, Option.CLASS_PATH);
        }

        @Override
        Collection<Path> getPaths() {
            lazy();
            return searchPath;
        }

        @Override
        protected SearchPath computePath(String value) {
            String cp = value;

            // CLASSPATH environment variable when run from `javac'.
            if (cp == null) {
                cp = System.getProperty("env.class.path");
            }

            // If invoked via a java VM (not the javac launcher), use the
            // platform class path
            if (cp == null && System.getProperty("application.home") == null) {
                cp = System.getProperty("java.class.path");
            }

            // Default to current working directory.
            if (cp == null) {
                cp = ".";
            }

            return createPath().addFiles(cp);
        }

        @Override
        protected SearchPath createPath() {
            return new SearchPath()
                    .expandJarClassPaths(true) // Only search user jars for Class-Paths
                    .emptyPathDefault(getPath("."));  // Empty path elt ==> current directory
        }

        private void lazy() {
            if (searchPath == null) {
                setPaths(null);
            }
        }
    }

    
Custom subtype of LocationHandler for PLATFORM_CLASS_PATH.
Various options are supported for different components of the
platform class path.
Setting a value with setLocation overrides all existing option values.
Setting any option overrides any value set with setLocation, and
reverts to using default values for options that have not been set.
Setting -bootclasspath or -Xbootclasspath overrides any existing
value for -Xbootclasspath/p: and -Xbootclasspath/a:.
/**
     * Custom subtype of LocationHandler for PLATFORM_CLASS_PATH.
     * Various options are supported for different components of the
     * platform class path.
     * Setting a value with setLocation overrides all existing option values.
     * Setting any option overrides any value set with setLocation, and
     * reverts to using default values for options that have not been set.
     * Setting -bootclasspath or -Xbootclasspath overrides any existing
     * value for -Xbootclasspath/p: and -Xbootclasspath/a:.
     */
    private class BootClassPathLocationHandler extends BasicLocationHandler {

        private Collection<Path> searchPath;
        final Map<Option, String> optionValues = new EnumMap<>(Option.class);

        
Is the bootclasspath the default?
/**
         * Is the bootclasspath the default?
         */
        private boolean isDefault;

        BootClassPathLocationHandler() {
            super(StandardLocation.PLATFORM_CLASS_PATH,
                    Option.BOOT_CLASS_PATH, Option.XBOOTCLASSPATH,
                    Option.XBOOTCLASSPATH_PREPEND,
                    Option.XBOOTCLASSPATH_APPEND,
                    Option.ENDORSEDDIRS, Option.DJAVA_ENDORSED_DIRS,
                    Option.EXTDIRS, Option.DJAVA_EXT_DIRS);
        }

        boolean isDefault() {
            lazy();
            return isDefault;
        }

        @Override
        boolean handleOption(Option option, String value) {
            if (!options.contains(option)) {
                return false;
            }

            option = canonicalize(option);
            optionValues.put(option, value);
            if (option == BOOT_CLASS_PATH) {
                optionValues.remove(XBOOTCLASSPATH_PREPEND);
                optionValues.remove(XBOOTCLASSPATH_APPEND);
            }
            searchPath = null;  // reset to "uninitialized"
            return true;
        }
        // where
        // TODO: would be better if option aliasing was handled at a higher
        // level
        private Option canonicalize(Option option) {
            switch (option) {
                case XBOOTCLASSPATH:
                    return Option.BOOT_CLASS_PATH;
                case DJAVA_ENDORSED_DIRS:
                    return Option.ENDORSEDDIRS;
                case DJAVA_EXT_DIRS:
                    return Option.EXTDIRS;
                default:
                    return option;
            }
        }

        @Override
        Collection<Path> getPaths() {
            lazy();
            return searchPath;
        }

        @Override
        void setPaths(Iterable<? extends Path> files) {
            if (files == null) {
                searchPath = null;  // reset to "uninitialized"
            } else {
                isDefault = false;
                SearchPath p = new SearchPath().addFiles(files, false);
                searchPath = Collections.unmodifiableCollection(p);
                optionValues.clear();
            }
        }

        SearchPath computePath() throws IOException {
            SearchPath path = new SearchPath();

            String bootclasspathOpt = optionValues.get(BOOT_CLASS_PATH);
            String endorseddirsOpt = optionValues.get(ENDORSEDDIRS);
            String extdirsOpt = optionValues.get(EXTDIRS);
            String xbootclasspathPrependOpt = optionValues.get(XBOOTCLASSPATH_PREPEND);
            String xbootclasspathAppendOpt = optionValues.get(XBOOTCLASSPATH_APPEND);
            path.addFiles(xbootclasspathPrependOpt);

            if (endorseddirsOpt != null) {
                path.addDirectories(endorseddirsOpt);
            } else {
                path.addDirectories(System.getProperty("java.endorsed.dirs"), false);
            }

            if (bootclasspathOpt != null) {
                path.addFiles(bootclasspathOpt);
            } else {
                // Standard system classes for this compiler's release.
                Collection<Path> systemClasses = systemClasses();
                if (systemClasses != null) {
                    path.addFiles(systemClasses, false);
                } else {
                    // fallback to the value of sun.boot.class.path
                    String files = System.getProperty("sun.boot.class.path");
                    path.addFiles(files, false);
                }
            }

            path.addFiles(xbootclasspathAppendOpt);

            // Strictly speaking, standard extensions are not bootstrap
            // classes, but we treat them identically, so we'll pretend
            // that they are.
            if (extdirsOpt != null) {
                path.addDirectories(extdirsOpt);
            } else {
                // Add lib/jfxrt.jar to the search path
               Path jfxrt = javaHome.resolve("lib/jfxrt.jar");
                if (Files.exists(jfxrt)) {
                    path.addFile(jfxrt, false);
                }
                path.addDirectories(System.getProperty("java.ext.dirs"), false);
            }

            isDefault =
                       (xbootclasspathPrependOpt == null)
                    && (bootclasspathOpt == null)
                    && (xbootclasspathAppendOpt == null);

            return path;
        }

        
Return a collection of files containing system classes. Returns null if not running on a modular image. 
Throws:
UncheckedIOException – if an I/O errors occurs/**
         * Return a collection of files containing system classes.
         * Returns {@code null} if not running on a modular image.
         *
         * @throws UncheckedIOException if an I/O errors occurs
         */
        private Collection<Path> systemClasses() throws IOException {
            // Return "modules" jimage file if available
            if (Files.isRegularFile(thisSystemModules)) {
                return Collections.singleton(thisSystemModules);
            }

            // Exploded module image
            Path modules = javaHome.resolve("modules");
            if (Files.isDirectory(modules.resolve("java.base"))) {
                try (Stream<Path> listedModules = Files.list(modules)) {
                    return listedModules.collect(Collectors.toList());
                }
            }

            // not a modular image that we know about
            return null;
        }

        private void lazy() {
            if (searchPath == null) {
                try {
                    searchPath = Collections.unmodifiableCollection(computePath());
                } catch (IOException e) {
                    // TODO: need better handling here, e.g. javac Abort?
                    throw new UncheckedIOException(e);
                }
            }
        }

        @Override
        boolean contains(Path file) throws IOException {
            return Locations.this.contains(searchPath, file);
        }
    }

    
A LocationHander to represent modules found from a module-oriented location such as MODULE_SOURCE_PATH, UPGRADE_MODULE_PATH, SYSTEM_MODULES and MODULE_PATH. The Location can be specified to accept overriding classes from the --patch-module <module>=<path>  parameter. /**
     * A LocationHander to represent modules found from a module-oriented
     * location such as MODULE_SOURCE_PATH, UPGRADE_MODULE_PATH,
     * SYSTEM_MODULES and MODULE_PATH.
     *
     * The Location can be specified to accept overriding classes from the
     * {@code --patch-module <module>=<path> } parameter.
     */
    private class ModuleLocationHandler extends LocationHandler implements Location {
        private final LocationHandler parent;
        private final String name;
        private final String moduleName;
        private final boolean output;
        Collection<Path> searchPath;

        ModuleLocationHandler(LocationHandler parent, String name, String moduleName,
                Collection<Path> searchPath, boolean output) {
            this.parent = parent;
            this.name = name;
            this.moduleName = moduleName;
            this.searchPath = searchPath;
            this.output = output;
        }

        @Override @DefinedBy(Api.COMPILER)
        public String getName() {
            return name;
        }

        @Override @DefinedBy(Api.COMPILER)
        public boolean isOutputLocation() {
            return output;
        }

        @Override // defined by LocationHandler
        boolean handleOption(Option option, String value) {
            throw new UnsupportedOperationException();
        }

        @Override // defined by LocationHandler
        Collection<Path> getPaths() {
            return Collections.unmodifiableCollection(searchPath);
        }

        @Override // defined by LocationHandler
        void setPaths(Iterable<? extends Path> paths) throws IOException {
            // defer to the parent to determine if this is acceptable
            parent.setPathsForModule(moduleName, paths);
        }

        @Override // defined by LocationHandler
        void setPathsForModule(String moduleName, Iterable<? extends Path> paths) {
            throw new UnsupportedOperationException("not supported for " + name);
        }

        @Override // defined by LocationHandler
        String inferModuleName() {
            return moduleName;
        }

        @Override
        boolean contains(Path file) throws IOException {
            return Locations.this.contains(searchPath, file);
        }

        @Override
        public String toString() {
            return name;
        }
    }

    
A table of module location handlers, indexed by name and path.
/**
     * A table of module location handlers, indexed by name and path.
     */
    private class ModuleTable {
        private final Map<String, ModuleLocationHandler> nameMap = new LinkedHashMap<>();
        private final Map<Path, ModuleLocationHandler> pathMap = new LinkedHashMap<>();

        void add(ModuleLocationHandler h) {
            nameMap.put(h.moduleName, h);
            for (Path p : h.searchPath) {
                pathMap.put(normalize(p), h);
            }
        }

        void updatePaths(ModuleLocationHandler h) {
            // use iterator, to be able to remove old entries
            for (Iterator<Map.Entry<Path, ModuleLocationHandler>> iter = pathMap.entrySet().iterator();
                    iter.hasNext(); ) {
                Map.Entry<Path, ModuleLocationHandler> e = iter.next();
                if (e.getValue() == h) {
                    iter.remove();
                }
            }
            for (Path p : h.searchPath) {
                pathMap.put(normalize(p), h);
            }
        }

        ModuleLocationHandler get(String name) {
            return nameMap.get(name);
        }

        ModuleLocationHandler get(Path path) {
            while (path != null) {
                ModuleLocationHandler l = pathMap.get(path);

                if (l != null)
                    return l;

                path = path.getParent();
            }

            return null;
        }

        void clear() {
            nameMap.clear();
            pathMap.clear();
        }

        boolean isEmpty() {
            return nameMap.isEmpty();
        }

        boolean contains(Path file) throws IOException {
            return Locations.this.contains(pathMap.keySet(), file);
        }

        Set<Location> locations() {
            return Collections.unmodifiableSet(nameMap.values().stream().collect(Collectors.toSet()));
        }
    }

    
A LocationHandler for simple module-oriented search paths,
like UPGRADE_MODULE_PATH and MODULE_PATH.
/**
     * A LocationHandler for simple module-oriented search paths,
     * like UPGRADE_MODULE_PATH and MODULE_PATH.
     */
    private class ModulePathLocationHandler extends SimpleLocationHandler {
        private ModuleTable moduleTable;

        ModulePathLocationHandler(Location location, Option... options) {
            super(location, options);
        }

        @Override
        public boolean handleOption(Option option, String value) {
            if (!options.contains(option)) {
                return false;
            }
            setPaths(value == null ? null : getPathEntries(value));
            return true;
        }

        @Override
        public Location getLocationForModule(String moduleName) {
            initModuleLocations();
            return moduleTable.get(moduleName);
        }

        @Override
        public Location getLocationForModule(Path file) {
            initModuleLocations();
            return moduleTable.get(file);
        }

        @Override
        Iterable<Set<Location>> listLocationsForModules() {
            if (searchPath == null)
                return Collections.emptyList();

            return ModulePathIterator::new;
        }

        @Override
        boolean contains(Path file) throws IOException {
            if (moduleTable == null) {
                initModuleLocations();
            }
            return moduleTable.contains(file);
        }

        @Override
        void setPaths(Iterable<? extends Path> paths) {
            if (paths != null) {
                for (Path p: paths) {
                    checkValidModulePathEntry(p);
                }
            }
            super.setPaths(paths);
            moduleTable = null;
        }

        @Override
        void setPathsForModule(String name, Iterable<? extends Path> paths) throws IOException {
            List<Path> checkedPaths = checkPaths(paths);
            // how far should we go to validate the paths provide a module?
            // e.g. contain module-info with the correct name?
            initModuleLocations();
            ModuleLocationHandler l = moduleTable.get(name);
            if (l == null) {
                l = new ModuleLocationHandler(this, location.getName() + "[" + name + "]",
                        name, checkedPaths, true);
                moduleTable.add(l);
           } else {
                l.searchPath = checkedPaths;
                moduleTable.updatePaths(l);
            }
        }

        private List<Path> checkPaths(Iterable<? extends Path> paths) throws IOException {
            Objects.requireNonNull(paths);
            List<Path> validPaths = new ArrayList<>();
            for (Path p : paths) {
                validPaths.add(checkDirectory(p));
            }
            return validPaths;
        }

        private void initModuleLocations() {
            if (moduleTable != null) {
                return;
            }

            moduleTable = new ModuleTable();

            for (Set<Location> set : listLocationsForModules()) {
                for (Location locn : set) {
                    if (locn instanceof ModuleLocationHandler) {
                        ModuleLocationHandler l = (ModuleLocationHandler) locn;
                        if (!moduleTable.nameMap.containsKey(l.moduleName)) {
                            moduleTable.add(l);
                        }
                    }
                }
            }
        }

        private void checkValidModulePathEntry(Path p) {
            if (!Files.exists(p)) {
                // warning may be generated later
                return;
            }

            if (Files.isDirectory(p)) {
                // either an exploded module or a directory of modules
                return;
            }

            String name = p.getFileName().toString();
            int lastDot = name.lastIndexOf(".");
            if (lastDot > 0) {
                switch (name.substring(lastDot)) {
                    case ".jar":
                    case ".jmod":
                        return;
                }
            }
            throw new IllegalArgumentException(p.toString());
        }

        class ModulePathIterator implements Iterator<Set<Location>> {
            Iterator<Path> pathIter = searchPath.iterator();
            int pathIndex = 0;
            Set<Location> next = null;

            @Override
            public boolean hasNext() {
                if (next != null)
                    return true;

                while (next == null) {
                    if (pathIter.hasNext()) {
                        Path path = pathIter.next();
                        if (Files.isDirectory(path)) {
                            next = scanDirectory(path);
                        } else {
                            next = scanFile(path);
                        }
                        pathIndex++;
                    } else
                        return false;
                }
                return true;
            }

            @Override
            public Set<Location> next() {
                hasNext();
                if (next != null) {
                    Set<Location> result = next;
                    next = null;
                    return result;
                }
                throw new NoSuchElementException();
            }

            private Set<Location> scanDirectory(Path path) {
                Set<Path> paths = new LinkedHashSet<>();
                Path moduleInfoClass = null;
                try (DirectoryStream<Path> stream = Files.newDirectoryStream(path)) {
                    for (Path entry: stream) {
                        if (entry.endsWith("module-info.class")) {
                            moduleInfoClass = entry;
                            break;  // no need to continue scanning
                        }
                        paths.add(entry);
                    }
                } catch (DirectoryIteratorException | IOException ignore) {
                    log.error(Errors.LocnCantReadDirectory(path));
                    return Collections.emptySet();
                }

                if (moduleInfoClass != null) {
                    // It's an exploded module directly on the module path.
                    // We can't infer module name from the directory name, so have to
                    // read module-info.class.
                    try {
                        String moduleName = readModuleName(moduleInfoClass);
                        String name = location.getName()
                                + "[" + pathIndex + ":" + moduleName + "]";
                        ModuleLocationHandler l = new ModuleLocationHandler(
                                ModulePathLocationHandler.this, name, moduleName,
                                Collections.singletonList(path), false);
                        return Collections.singleton(l);
                    } catch (ModuleNameReader.BadClassFile e) {
                        log.error(Errors.LocnBadModuleInfo(path));
                        return Collections.emptySet();
                    } catch (IOException e) {
                        log.error(Errors.LocnCantReadFile(path));
                        return Collections.emptySet();
                    }
                }

                // A directory of modules
                Set<Location> result = new LinkedHashSet<>();
                int index = 0;
                for (Path entry : paths) {
                    Pair<String,Path> module = inferModuleName(entry);
                    if (module == null) {
                        // diagnostic reported if necessary; skip to next
                        continue;
                    }
                    String moduleName = module.fst;
                    Path modulePath = module.snd;
                    String name = location.getName()
                            + "[" + pathIndex + "." + (index++) + ":" + moduleName + "]";
                    ModuleLocationHandler l = new ModuleLocationHandler(
                            ModulePathLocationHandler.this, name, moduleName,
                            Collections.singletonList(modulePath), false);
                    result.add(l);
                }
                return result;
            }

            private Set<Location> scanFile(Path path) {
                Pair<String,Path> module = inferModuleName(path);
                if (module == null) {
                    // diagnostic reported if necessary
                    return Collections.emptySet();
                }
                String moduleName = module.fst;
                Path modulePath = module.snd;
                String name = location.getName()
                        + "[" + pathIndex + ":" + moduleName + "]";
                ModuleLocationHandler l = new ModuleLocationHandler(
                        ModulePathLocationHandler.this, name, moduleName,
                        Collections.singletonList(modulePath), false);
                return Collections.singleton(l);
            }

            private Pair<String,Path> inferModuleName(Path p) {
                if (Files.isDirectory(p)) {
                    if (Files.exists(p.resolve("module-info.class"))) {
                        String name = p.getFileName().toString();
                        if (SourceVersion.isName(name))
                            return new Pair<>(name, p);
                    }
                    return null;
                }

                if (p.getFileName().toString().endsWith(".jar") && fsInfo.exists(p)) {
                    FileSystemProvider jarFSProvider = fsInfo.getJarFSProvider();
                    if (jarFSProvider == null) {
                        log.error(Errors.NoZipfsForArchive(p));
                        return null;
                    }
                    try (FileSystem fs = jarFSProvider.newFileSystem(p, fsEnv)) {
                        Path moduleInfoClass = fs.getPath("module-info.class");
                        if (Files.exists(moduleInfoClass)) {
                            String moduleName = readModuleName(moduleInfoClass);
                            return new Pair<>(moduleName, p);
                        }
                        Path mf = fs.getPath("META-INF/MANIFEST.MF");
                        if (Files.exists(mf)) {
                            try (InputStream in = Files.newInputStream(mf)) {
                                Manifest man = new Manifest(in);
                                Attributes attrs = man.getMainAttributes();
                                if (attrs != null) {
                                    String moduleName = attrs.getValue(new Attributes.Name("Automatic-Module-Name"));
                                    if (moduleName != null) {
                                        if (isModuleName(moduleName)) {
                                            return new Pair<>(moduleName, p);
                                        } else {
                                            log.error(Errors.LocnCantGetModuleNameForJar(p));
                                            return null;
                                        }
                                    }
                                }
                            }
                        }
                    } catch (ModuleNameReader.BadClassFile e) {
                        log.error(Errors.LocnBadModuleInfo(p));
                        return null;
                    } catch (IOException e) {
                        log.error(Errors.LocnCantReadFile(p));
                        return null;
                    }

                    //automatic module:
                    String fn = p.getFileName().toString();
                    //from ModulePath.deriveModuleDescriptor:

                    // drop .jar
                    String mn = fn.substring(0, fn.length()-4);

                    // find first occurrence of -${NUMBER}. or -${NUMBER}$
                    Matcher matcher = Pattern.compile("-(\\d+(\\.|$))").matcher(mn);
                    if (matcher.find()) {
                        int start = matcher.start();

                        mn = mn.substring(0, start);
                    }

                    // finally clean up the module name
                    mn =  mn.replaceAll("[^A-Za-z0-9]", ".")  // replace non-alphanumeric
                            .replaceAll("(\\.)(\\1)+", ".")   // collapse repeating dots
                            .replaceAll("^\\.", "")           // drop leading dots
                            .replaceAll("\\.$", "");          // drop trailing dots


                    if (!mn.isEmpty()) {
                        return new Pair<>(mn, p);
                    }

                    log.error(Errors.LocnCantGetModuleNameForJar(p));
                    return null;
                }

                if (p.getFileName().toString().endsWith(".jmod")) {
                    try {
                        // check if the JMOD file is valid
                        JDK9Wrappers.JmodFile.checkMagic(p);

                        // No JMOD file system.  Use JarFileSystem to
                        // workaround for now
                        FileSystem fs = fileSystems.get(p);
                        if (fs == null) {
                            FileSystemProvider jarFSProvider = fsInfo.getJarFSProvider();
                            if (jarFSProvider == null) {
                                log.error(Errors.LocnCantReadFile(p));
                                return null;
                            }
                            fs = jarFSProvider.newFileSystem(p, Collections.emptyMap());
                            try {
                                Path moduleInfoClass = fs.getPath("classes/module-info.class");
                                String moduleName = readModuleName(moduleInfoClass);
                                Path modulePath = fs.getPath("classes");
                                fileSystems.put(p, fs);
                                closeables.add(fs);
                                fs = null; // prevent fs being closed in the finally clause
                                return new Pair<>(moduleName, modulePath);
                            } finally {
                                if (fs != null)
                                    fs.close();
                            }
                        }
                    } catch (ModuleNameReader.BadClassFile e) {
                        log.error(Errors.LocnBadModuleInfo(p));
                    } catch (IOException e) {
                        log.error(Errors.LocnCantReadFile(p));
                        return null;
                    }
                }

                if (warn && false) {  // temp disable, when enabled, massage examples.not-yet.txt suitably.
                    log.warning(Warnings.LocnUnknownFileOnModulePath(p));
                }
                return null;
            }

            private String readModuleName(Path path) throws IOException, ModuleNameReader.BadClassFile {
                if (moduleNameReader == null)
                    moduleNameReader = new ModuleNameReader();
                return moduleNameReader.readModuleName(path);
            }
        }

        //from jdk.internal.module.Checks:
        
Returns true if the given name is a legal module name. /**
         * Returns {@code true} if the given name is a legal module name.
         */
        private boolean isModuleName(String name) {
            int next;
            int off = 0;
            while ((next = name.indexOf('.', off)) != -1) {
                String id = name.substring(off, next);
                if (!SourceVersion.isName(id))
                    return false;
                off = next+1;
            }
            String last = name.substring(off);
            return SourceVersion.isName(last);
        }
    }

    private class ModuleSourcePathLocationHandler extends BasicLocationHandler {
        private ModuleTable moduleTable;
        private List<Path> paths;

        ModuleSourcePathLocationHandler() {
            super(StandardLocation.MODULE_SOURCE_PATH,
                    Option.MODULE_SOURCE_PATH);
        }

        @Override
        boolean handleOption(Option option, String value) {
            init(value);
            return true;
        }

        void init(String value) {
            Collection<String> segments = new ArrayList<>();
            for (String s: value.split(File.pathSeparator)) {
                expandBraces(s, segments);
            }

            Map<String, List<Path>> map = new LinkedHashMap<>();
            List<Path> noSuffixPaths = new ArrayList<>();
            boolean anySuffix = false;
            final String MARKER = "*";
            for (String seg: segments) {
                int markStart = seg.indexOf(MARKER);
                if (markStart == -1) {
                    Path p = getPath(seg);
                    add(map, p, null);
                    noSuffixPaths.add(p);
                } else {
                    if (markStart == 0 || !isSeparator(seg.charAt(markStart - 1))) {
                        throw new IllegalArgumentException("illegal use of " + MARKER + " in " + seg);
                    }
                    Path prefix = getPath(seg.substring(0, markStart - 1));
                    Path suffix;
                    int markEnd = markStart + MARKER.length();
                    if (markEnd == seg.length()) {
                        suffix = null;
                    } else if (!isSeparator(seg.charAt(markEnd))
                            || seg.indexOf(MARKER, markEnd) != -1) {
                        throw new IllegalArgumentException("illegal use of " + MARKER + " in " + seg);
                    } else {
                        suffix = getPath(seg.substring(markEnd + 1));
                        anySuffix = true;
                    }
                    add(map, prefix, suffix);
                    if (suffix == null) {
                        noSuffixPaths.add(prefix);
                    }
                }
            }

            initModuleTable(map);
            paths = anySuffix ? null : noSuffixPaths;
        }

        private void initModuleTable(Map<String, List<Path>> map) {
            moduleTable = new ModuleTable();
            map.forEach((modName, modPath) -> {
                boolean hasModuleInfo = modPath.stream().anyMatch(checkModuleInfo);
                if (hasModuleInfo) {
                    String locnName = location.getName() + "[" + modName + "]";
                    ModuleLocationHandler l = new ModuleLocationHandler(this, locnName, modName,
                            modPath, false);
                    moduleTable.add(l);
                }
            });
        }
        //where:
            private final Predicate<Path> checkModuleInfo =
                    p -> Files.exists(p.resolve("module-info.java"));


        private boolean isSeparator(char ch) {
            // allow both separators on Windows
            return (ch == File.separatorChar) || (ch == '/');
        }

        void add(Map<String, List<Path>> map, Path prefix, Path suffix) {
            if (!Files.isDirectory(prefix)) {
                if (warn) {
                    String key = Files.exists(prefix)
                            ? "dir.path.element.not.directory"
                            : "dir.path.element.not.found";
                    log.warning(Lint.LintCategory.PATH, key, prefix);
                }
                return;
            }
            try (DirectoryStream<Path> stream = Files.newDirectoryStream(prefix, path -> Files.isDirectory(path))) {
                for (Path entry: stream) {
                    Path path = (suffix == null) ? entry : entry.resolve(suffix);
                    if (Files.isDirectory(path)) {
                        String name = entry.getFileName().toString();
                        List<Path> paths = map.get(name);
                        if (paths == null)
                            map.put(name, paths = new ArrayList<>());
                        paths.add(path);
                    }
                }
            } catch (IOException e) {
                // TODO? What to do?
                System.err.println(e);
            }
        }

        private void expandBraces(String value, Collection<String> results) {
            int depth = 0;
            int start = -1;
            String prefix = null;
            String suffix = null;
            for (int i = 0; i < value.length(); i++) {
                switch (value.charAt(i)) {
                    case '{':
                        depth++;
                        if (depth == 1) {
                            prefix = value.substring(0, i);
                            suffix = value.substring(getMatchingBrace(value, i) + 1);
                            start = i + 1;
                        }
                        break;

                    case ',':
                        if (depth == 1) {
                            String elem = value.substring(start, i);
                            expandBraces(prefix + elem + suffix, results);
                            start = i + 1;
                        }
                        break;

                    case '}':
                        switch (depth) {
                            case 0:
                                throw new IllegalArgumentException("mismatched braces");

                            case 1:
                                String elem = value.substring(start, i);
                                expandBraces(prefix + elem + suffix, results);
                                return;

                            default:
                                depth--;
                        }
                        break;
                }
            }
            if (depth > 0)
                throw new IllegalArgumentException("mismatched braces");
            results.add(value);
        }

        int getMatchingBrace(String value, int offset) {
            int depth = 1;
            for (int i = offset + 1; i < value.length(); i++) {
                switch (value.charAt(i)) {
                    case '{':
                        depth++;
                        break;

                    case '}':
                        if (--depth == 0)
                            return i;
                        break;
                }
            }
            throw new IllegalArgumentException("mismatched braces");
        }

        @Override
        boolean isSet() {
            return (moduleTable != null);
        }

        @Override
        Collection<Path> getPaths() {
            if (paths == null) {
                // This may occur for a complex setting with --module-source-path option
                // i.e. one that cannot be represented by a simple series of paths.
                throw new IllegalStateException("paths not available");
            }
            return paths;
        }

        @Override
        void setPaths(Iterable<? extends Path> files) throws IOException {
            Map<String, List<Path>> map = new LinkedHashMap<>();
            List<Path> newPaths = new ArrayList<>();
            for (Path file : files) {
                add(map, file, null);
                newPaths.add(file);
            }

            initModuleTable(map);
            paths = Collections.unmodifiableList(newPaths);
        }

        @Override
        void setPathsForModule(String name, Iterable<? extends Path> paths) throws IOException {
            List<Path> validPaths = checkPaths(paths);

            if (moduleTable == null)
                moduleTable = new ModuleTable();

            ModuleLocationHandler l = moduleTable.get(name);
            if (l == null) {
                l = new ModuleLocationHandler(this,
                        location.getName() + "[" + name + "]",
                        name,
                        validPaths,
                        true);
                moduleTable.add(l);
           } else {
                l.searchPath = validPaths;
                moduleTable.updatePaths(l);
            }
        }

        private List<Path> checkPaths(Iterable<? extends Path> paths) throws IOException {
            Objects.requireNonNull(paths);
            List<Path> validPaths = new ArrayList<>();
            for (Path p : paths) {
                validPaths.add(checkDirectory(p));
            }
            return validPaths;
        }

        @Override
        Location getLocationForModule(String name) {
            return (moduleTable == null) ? null : moduleTable.get(name);
        }

        @Override
        Location getLocationForModule(Path file) {
            return (moduleTable == null) ? null : moduleTable.get(file);
        }

        @Override
        Iterable<Set<Location>> listLocationsForModules() {
            if (moduleTable == null)
                return Collections.emptySet();

            return Collections.singleton(moduleTable.locations());
        }

        @Override
        boolean contains(Path file) throws IOException {
            return (moduleTable == null) ? false : moduleTable.contains(file);
        }

    }

    private class SystemModulesLocationHandler extends BasicLocationHandler {
        private Path systemJavaHome;
        private Path modules;
        private ModuleTable moduleTable;

        SystemModulesLocationHandler() {
            super(StandardLocation.SYSTEM_MODULES, Option.SYSTEM);
            systemJavaHome = Locations.javaHome;
        }

        @Override
        boolean handleOption(Option option, String value) {
            if (!options.contains(option)) {
                return false;
            }

            if (value == null) {
                systemJavaHome = Locations.javaHome;
            } else if (value.equals("none")) {
                systemJavaHome = null;
            } else {
                update(getPath(value));
            }

            modules = null;
            return true;
        }

        @Override
        Collection<Path> getPaths() {
            return (systemJavaHome == null) ? null : Collections.singleton(systemJavaHome);
        }

        @Override
        void setPaths(Iterable<? extends Path> files) throws IOException {
            if (files == null) {
                systemJavaHome = null;
            } else {
                Path dir = checkSingletonDirectory(files);
                update(dir);
            }
        }

        @Override
        void setPathsForModule(String name, Iterable<? extends Path> paths) throws IOException {
            List<Path> checkedPaths = checkPaths(paths);
            initSystemModules();
            ModuleLocationHandler l = moduleTable.get(name);
            if (l == null) {
                l = new ModuleLocationHandler(this,
                        location.getName() + "[" + name + "]",
                        name,
                        checkedPaths,
                        true);
                moduleTable.add(l);
           } else {
                l.searchPath = checkedPaths;
                moduleTable.updatePaths(l);
            }
        }

        private List<Path> checkPaths(Iterable<? extends Path> paths) throws IOException {
            Objects.requireNonNull(paths);
            List<Path> validPaths = new ArrayList<>();
            for (Path p : paths) {
                validPaths.add(checkDirectory(p));
            }
            return validPaths;
        }

        private void update(Path p) {
            if (!isCurrentPlatform(p) && !Files.exists(p.resolve("lib").resolve("jrt-fs.jar")) &&
                    !Files.exists(systemJavaHome.resolve("modules")))
                throw new IllegalArgumentException(p.toString());
            systemJavaHome = p;
            modules = null;
        }

        private boolean isCurrentPlatform(Path p) {
            try {
                return Files.isSameFile(p, Locations.javaHome);
            } catch (IOException ex) {
                throw new IllegalArgumentException(p.toString(), ex);
            }
        }

        @Override
        Location getLocationForModule(String name) throws IOException {
            initSystemModules();
            return moduleTable.get(name);
        }

        @Override
        Location getLocationForModule(Path file) throws IOException {
            initSystemModules();
            return moduleTable.get(file);
        }

        @Override
        Iterable<Set<Location>> listLocationsForModules() throws IOException {
            initSystemModules();
            return Collections.singleton(moduleTable.locations());
        }

        @Override
        boolean contains(Path file) throws IOException {
            initSystemModules();
            return moduleTable.contains(file);
        }

        private void initSystemModules() throws IOException {
            if (moduleTable != null)
                return;

            if (systemJavaHome == null) {
                moduleTable = new ModuleTable();
                return;
            }

            if (modules == null) {
                try {
                    URI jrtURI = URI.create("jrt:/");
                    FileSystem jrtfs;

                    if (isCurrentPlatform(systemJavaHome)) {
                        jrtfs = FileSystems.getFileSystem(jrtURI);
                    } else {
                        try {
                            Map<String, String> attrMap =
                                    Collections.singletonMap("java.home", systemJavaHome.toString());
                            jrtfs = FileSystems.newFileSystem(jrtURI, attrMap);
                        } catch (ProviderNotFoundException ex) {
                            URL javaHomeURL = systemJavaHome.resolve("jrt-fs.jar").toUri().toURL();
                            ClassLoader currentLoader = Locations.class.getClassLoader();
                            URLClassLoader fsLoader =
                                    new URLClassLoader(new URL[] {javaHomeURL}, currentLoader);

                            jrtfs = FileSystems.newFileSystem(jrtURI, Collections.emptyMap(), fsLoader);

                            closeables.add(fsLoader);
                        }

                        closeables.add(jrtfs);
                    }

                    modules = jrtfs.getPath("/modules");
                } catch (FileSystemNotFoundException | ProviderNotFoundException e) {
                    modules = systemJavaHome.resolve("modules");
                    if (!Files.exists(modules))
                        throw new IOException("can't find system classes", e);
                }
            }

            moduleTable = new ModuleTable();
            try (DirectoryStream<Path> stream = Files.newDirectoryStream(modules, Files::isDirectory)) {
                for (Path entry : stream) {
                    String moduleName = entry.getFileName().toString();
                    String name = location.getName() + "[" + moduleName + "]";
                    ModuleLocationHandler h = new ModuleLocationHandler(this,
                            name, moduleName, Collections.singletonList(entry), false);
                    moduleTable.add(h);
                }
            }
        }
    }

    private class PatchModulesLocationHandler extends BasicLocationHandler {
        private final ModuleTable moduleTable = new ModuleTable();

        PatchModulesLocationHandler() {
            super(StandardLocation.PATCH_MODULE_PATH, Option.PATCH_MODULE);
        }

        @Override
        boolean handleOption(Option option, String value) {
            if (!options.contains(option)) {
                return false;
            }

            moduleTable.clear();

            // Allow an extended syntax for --patch-module consisting of a series
            // of values separated by NULL characters. This is to facilitate
            // supporting deferred file manager options on the command line.
            // See Option.PATCH_MODULE for the code that composes these multiple
            // values.
            for (String v : value.split("\0")) {
                int eq = v.indexOf('=');
                if (eq > 0) {
                    String moduleName = v.substring(0, eq);
                    SearchPath mPatchPath = new SearchPath()
                            .addFiles(v.substring(eq + 1));
                    String name = location.getName() + "[" + moduleName + "]";
                    ModuleLocationHandler h = new ModuleLocationHandler(this, name,
                            moduleName, mPatchPath, false);
                    moduleTable.add(h);
                } else {
                    // Should not be able to get here;
                    // this should be caught and handled in Option.PATCH_MODULE
                    log.error(Errors.LocnInvalidArgForXpatch(value));
                }
            }

            return true;
        }

        @Override
        boolean isSet() {
            return !moduleTable.isEmpty();
        }

        @Override
        Collection<Path> getPaths() {
            throw new UnsupportedOperationException();
        }

        @Override
        void setPaths(Iterable<? extends Path> files) throws IOException {
            throw new UnsupportedOperationException();
        }

        @Override // defined by LocationHandler
        void setPathsForModule(String moduleName, Iterable<? extends Path> files) throws IOException {
            throw new UnsupportedOperationException(); // not yet
        }

        @Override
        Location getLocationForModule(String name) throws IOException {
            return moduleTable.get(name);
        }

        @Override
        Location getLocationForModule(Path file) throws IOException {
            return moduleTable.get(file);
        }

        @Override
        Iterable<Set<Location>> listLocationsForModules() throws IOException {
            return Collections.singleton(moduleTable.locations());
        }

        @Override
        boolean contains(Path file) throws IOException {
            return moduleTable.contains(file);
        }
    }

    Map<Location, LocationHandler> handlersForLocation;
    Map<Option, LocationHandler> handlersForOption;

    void initHandlers() {
        handlersForLocation = new HashMap<>();
        handlersForOption = new EnumMap<>(Option.class);

        BasicLocationHandler[] handlers = {
            new BootClassPathLocationHandler(),
            new ClassPathLocationHandler(),
            new SimpleLocationHandler(StandardLocation.SOURCE_PATH, Option.SOURCE_PATH),
            new SimpleLocationHandler(StandardLocation.ANNOTATION_PROCESSOR_PATH, Option.PROCESSOR_PATH),
            new SimpleLocationHandler(StandardLocation.ANNOTATION_PROCESSOR_MODULE_PATH, Option.PROCESSOR_MODULE_PATH),
            new OutputLocationHandler(StandardLocation.CLASS_OUTPUT, Option.D),
            new OutputLocationHandler(StandardLocation.SOURCE_OUTPUT, Option.S),
            new OutputLocationHandler(StandardLocation.NATIVE_HEADER_OUTPUT, Option.H),
            new ModuleSourcePathLocationHandler(),
            new PatchModulesLocationHandler(),
            new ModulePathLocationHandler(StandardLocation.UPGRADE_MODULE_PATH, Option.UPGRADE_MODULE_PATH),
            new ModulePathLocationHandler(StandardLocation.MODULE_PATH, Option.MODULE_PATH),
            new SystemModulesLocationHandler(),
        };

        for (BasicLocationHandler h : handlers) {
            handlersForLocation.put(h.location, h);
            for (Option o : h.options) {
                handlersForOption.put(o, h);
            }
        }
    }

    boolean handleOption(Option option, String value) {
        LocationHandler h = handlersForOption.get(option);
        return (h == null ? false : h.handleOption(option, value));
    }

    boolean hasLocation(Location location) {
        LocationHandler h = getHandler(location);
        return (h == null ? false : h.isSet());
    }

    Collection<Path> getLocation(Location location) {
        LocationHandler h = getHandler(location);
        return (h == null ? null : h.getPaths());
    }

    Path getOutputLocation(Location location) {
        if (!location.isOutputLocation()) {
            throw new IllegalArgumentException();
        }
        LocationHandler h = getHandler(location);
        return ((OutputLocationHandler) h).outputDir;
    }

    void setLocation(Location location, Iterable<? extends Path> files) throws IOException {
        LocationHandler h = getHandler(location);
        if (h == null) {
            if (location.isOutputLocation()) {
                h = new OutputLocationHandler(location);
            } else {
                h = new SimpleLocationHandler(location);
            }
            handlersForLocation.put(location, h);
        }
        h.setPaths(files);
    }

    Location getLocationForModule(Location location, String name) throws IOException {
        LocationHandler h = getHandler(location);
        return (h == null ? null : h.getLocationForModule(name));
    }

    Location getLocationForModule(Location location, Path file) throws IOException {
        LocationHandler h = getHandler(location);
        return (h == null ? null : h.getLocationForModule(file));
    }

    void setLocationForModule(Location location, String moduleName,
            Iterable<? extends Path> files) throws IOException {
        LocationHandler h = getHandler(location);
        if (h == null) {
            if (location.isOutputLocation()) {
                h = new OutputLocationHandler(location);
            } else {
                h = new ModulePathLocationHandler(location);
            }
            handlersForLocation.put(location, h);
        }
        h.setPathsForModule(moduleName, files);
    }

    String inferModuleName(Location location) {
        LocationHandler h = getHandler(location);
        return (h == null ? null : h.inferModuleName());
    }

    Iterable<Set<Location>> listLocationsForModules(Location location) throws IOException {
        LocationHandler h = getHandler(location);
        return (h == null ? null : h.listLocationsForModules());
    }

    boolean contains(Location location, Path file) throws IOException {
        LocationHandler h = getHandler(location);
        if (h == null)
            throw new IllegalArgumentException("unknown location");
        return h.contains(file);
    }

    protected LocationHandler getHandler(Location location) {
        Objects.requireNonNull(location);
        return (location instanceof LocationHandler)
                ? (LocationHandler) location
                : handlersForLocation.get(location);
    }

    
Is this the name of an archive file?
/**
     * Is this the name of an archive file?
     */
    private boolean isArchive(Path file) {
        String n = StringUtils.toLowerCase(file.getFileName().toString());
        return fsInfo.isFile(file)
                && (n.endsWith(".jar") || n.endsWith(".zip"));
    }

    static Path normalize(Path p) {
        try {
            return p.toRealPath();
        } catch (IOException e) {
            return p.toAbsolutePath().normalize();
        }
    }
}