src/main/java/com/google/devtools/build/lib/skyframe/FileStateValue.java - bazel - Git at Google

 // Copyright 2014 The Bazel Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //    http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 package com.google.devtools.build.lib.skyframe;

 import com.google.common.annotations.VisibleForTesting;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.util.Preconditions;
 import com.google.devtools.build.lib.util.io.TimestampGranularityMonitor;
 import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.FileStatusWithDigest;
 import com.google.devtools.build.lib.vfs.FileStatusWithDigestAdapter;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.lib.vfs.RootedPath;
 import com.google.devtools.build.lib.vfs.Symlinks;
 import com.google.devtools.build.skyframe.LegacySkyKey;
 import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Objects;
 import javax.annotation.Nullable;

 /**
  * Encapsulates the filesystem operations needed to get state for a path. This is at least a
  * 'lstat' to determine what type of file the path is.
  * <ul>
  *   <li> For a non-existent file, the non existence is noted.
  *   <li> For a symlink, the symlink target is noted.
  *   <li> For a directory, the existence is noted.
  *   <li> For a file, the existence is noted, along with metadata about the file (e.g.
  *        file digest). See {@link RegularFileStateValue}.
  * <ul>
  *
  * <p>This class is an implementation detail of {@link FileValue} and should not be used outside of
  * {@link FileFunction}. Instead, {@link FileValue} should be used by consumers that care about
  * files.
  *
  * <p>All subclasses must implement {@link #equals} and {@link #hashCode} properly.
  */
 @VisibleForTesting
 public abstract class FileStateValue implements SkyValue {

   public static final DirectoryFileStateValue DIRECTORY_FILE_STATE_NODE =
       new DirectoryFileStateValue();
   public static final NonexistentFileStateValue NONEXISTENT_FILE_STATE_NODE =
       new NonexistentFileStateValue();

   /** Type of a path. */
   public enum Type {
     REGULAR_FILE,
     SPECIAL_FILE,
     DIRECTORY,
     SYMLINK,
     NONEXISTENT,
   }

   protected FileStateValue() {
   }

   public static FileStateValue create(RootedPath rootedPath,
       @Nullable TimestampGranularityMonitor tsgm) throws InconsistentFilesystemException,
       IOException {
     Path path = rootedPath.asPath();
     // Stat, but don't throw an exception for the common case of a nonexistent file. This still
     // throws an IOException in case any other IO error is encountered.
     FileStatus stat = path.statIfFound(Symlinks.NOFOLLOW);
     if (stat == null) {
       return NONEXISTENT_FILE_STATE_NODE;
     }
     return createWithStatNoFollow(rootedPath, FileStatusWithDigestAdapter.adapt(stat), tsgm);
   }

   static FileStateValue createWithStatNoFollow(RootedPath rootedPath,
       FileStatusWithDigest statNoFollow, @Nullable TimestampGranularityMonitor tsgm)
           throws InconsistentFilesystemException, IOException {
     Path path = rootedPath.asPath();
     if (statNoFollow.isFile()) {
       return statNoFollow.isSpecialFile()
           ? SpecialFileStateValue.fromStat(path.asFragment(), statNoFollow, tsgm)
           : RegularFileStateValue.fromPath(path, statNoFollow, tsgm);
     } else if (statNoFollow.isDirectory()) {
       return DIRECTORY_FILE_STATE_NODE;
     } else if (statNoFollow.isSymbolicLink()) {
       return new SymlinkFileStateValue(path.readSymbolicLinkUnchecked());
     }
     throw new InconsistentFilesystemException("according to stat, existing path " + path + " is "
         + "neither a file nor directory nor symlink.");
   }

   @VisibleForTesting
   @ThreadSafe
   public static SkyKey key(RootedPath rootedPath) {
     return LegacySkyKey.create(SkyFunctions.FILE_STATE, rootedPath);
   }

   public abstract Type getType();

   PathFragment getSymlinkTarget() {
     throw new IllegalStateException();
   }

   long getSize() {
     throw new IllegalStateException();
   }

   @Nullable
   byte[] getDigest() {
     throw new IllegalStateException();
   }

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

   abstract String prettyPrint();

   /**
    * Implementation of {@link FileStateValue} for regular files that exist.
    *
    * <p>A union of (digest, mtime). We use digests only if a fast digest lookup is available from
    * the filesystem. If not, we fall back to mtime-based digests. This avoids the case where Blaze
    * must read all files involved in the build in order to check for modifications in the case
    * where fast digest lookups are not available.
    */
   @ThreadSafe
   public static final class RegularFileStateValue extends FileStateValue {
     private final long size;
     // Only needed for empty-file equality-checking. Otherwise is always -1.
     // TODO(bazel-team): Consider getting rid of this special case for empty files.
     private final long mtime;
     @Nullable private final byte[] digest;
     @Nullable private final FileContentsProxy contentsProxy;

     public RegularFileStateValue(long size, long mtime, byte[] digest,
         FileContentsProxy contentsProxy) {
       Preconditions.checkState((digest == null) != (contentsProxy == null));
       this.size = size;
       // mtime is forced to be -1 so that we do not accidentally depend on it for non-empty files,
       // which should only be compared using digests.
       this.mtime = size == 0 ? mtime : -1;
       this.digest = digest;
       this.contentsProxy = contentsProxy;
     }

     /**
      * Create a FileFileStateValue instance corresponding to the given existing file.
      * @param stat must be of type "File". (Not a symlink).
      */
     private static RegularFileStateValue fromPath(Path path, FileStatusWithDigest stat,
                                         @Nullable TimestampGranularityMonitor tsgm)
         throws InconsistentFilesystemException {
       Preconditions.checkState(stat.isFile(), path);

       try {
         byte[] digest = tryGetDigest(path, stat);
         if (digest == null) {
           long mtime = stat.getLastModifiedTime();
           // Note that TimestampGranularityMonitor#notifyDependenceOnFileTime is a thread-safe
           // method.
           if (tsgm != null) {
             tsgm.notifyDependenceOnFileTime(path.asFragment(), mtime);
           }
           return new RegularFileStateValue(stat.getSize(), stat.getLastModifiedTime(), null,
               FileContentsProxy.create(stat));
         } else {
           // We are careful here to avoid putting the value ID into FileMetadata if we already have
           // a digest. Arbitrary filesystems may do weird things with the value ID; a digest is more
           // robust.
           return new RegularFileStateValue(stat.getSize(), stat.getLastModifiedTime(), digest, null);
         }
       } catch (IOException e) {
         String errorMessage = e.getMessage() != null
             ? "error '" + e.getMessage() + "'" : "an error";
         throw new InconsistentFilesystemException("'stat' said " + path + " is a file but then we "
             + "later encountered " + errorMessage + " which indicates that " + path + " is no "
             + "longer a file. Did you delete it during the build?");
       }
     }

     @Nullable
     private static byte[] tryGetDigest(Path path, FileStatusWithDigest stat) throws IOException {
       try {
         byte[] digest = stat.getDigest();
         return digest != null ? digest : path.getFastDigest();
       } catch (IOException ioe) {
         if (!path.isReadable()) {
           return null;
         }
         throw ioe;
       }
     }

     @Override
     public Type getType() {
       return Type.REGULAR_FILE;
     }

     @Override
     public long getSize() {
       return size;
     }

     public long getMtime() {
       return mtime;
     }

     @Override
     @Nullable
     public byte[] getDigest() {
       return digest;
     }

     public FileContentsProxy getContentsProxy() {
       return contentsProxy;
     }

     @Override
     public boolean equals(Object obj) {
       if (obj instanceof RegularFileStateValue) {
         RegularFileStateValue other = (RegularFileStateValue) obj;
         return size == other.size && mtime == other.mtime && Arrays.equals(digest, other.digest)
             && Objects.equals(contentsProxy, other.contentsProxy);
       }
       return false;
     }

     @Override
     public int hashCode() {
       return Objects.hash(size, mtime, Arrays.hashCode(digest), contentsProxy);
     }

     @Override
     public String prettyPrint() {
       String contents = digest != null
           ? String.format("digest of %s", Arrays.toString(digest))
           : contentsProxy.prettyPrint();
       String extra = mtime != -1 ? String.format(" and mtime of %d", mtime) : "";
       return String.format("regular file with size of %d and %s%s", size, contents, extra);
     }
   }

   /** Implementation of {@link FileStateValue} for special files that exist. */
   public static final class SpecialFileStateValue extends FileStateValue {
     private final FileContentsProxy contentsProxy;

     public SpecialFileStateValue(FileContentsProxy contentsProxy) {
       this.contentsProxy = contentsProxy;
     }

     static SpecialFileStateValue fromStat(PathFragment path, FileStatusWithDigest stat,
         @Nullable TimestampGranularityMonitor tsgm) throws IOException {
       long mtime = stat.getLastModifiedTime();
       // Note that TimestampGranularityMonitor#notifyDependenceOnFileTime is a thread-safe
       // method.
       if (tsgm != null) {
         tsgm.notifyDependenceOnFileTime(path, mtime);
       }
       return new SpecialFileStateValue(FileContentsProxy.create(stat));
     }

     @Override
     public Type getType() {
       return Type.SPECIAL_FILE;
     }

     @Override
     long getSize() {
       return 0;
     }

     @Override
     @Nullable
     byte[] getDigest() {
       return null;
     }

     public FileContentsProxy getContentsProxy() {
       return contentsProxy;
     }

     @Override
     public boolean equals(Object obj) {
       if (obj instanceof SpecialFileStateValue) {
         SpecialFileStateValue other = (SpecialFileStateValue) obj;
         return Objects.equals(contentsProxy, other.contentsProxy);
       }
       return false;
     }

     @Override
     public int hashCode() {
       return contentsProxy.hashCode();
     }

     @Override
     public String prettyPrint() {
       return String.format("special file with %s", contentsProxy.prettyPrint());
     }
   }

   /** Implementation of {@link FileStateValue} for directories that exist. */
   public static final class DirectoryFileStateValue extends FileStateValue {

     private DirectoryFileStateValue() {
     }

     @Override
     public Type getType() {
       return Type.DIRECTORY;
     }

     @Override
     public String prettyPrint() {
       return "directory";
     }

     // This object is normally a singleton, but deserialization produces copies.
     @Override
     public boolean equals(Object obj) {
       return obj instanceof DirectoryFileStateValue;
     }

     @Override
     public int hashCode() {
       return 7654321;
     }
   }

   /** Implementation of {@link FileStateValue} for symlinks. */
   public static final class SymlinkFileStateValue extends FileStateValue {

     private final PathFragment symlinkTarget;

     public SymlinkFileStateValue(PathFragment symlinkTarget) {
       this.symlinkTarget = symlinkTarget;
     }

     @Override
     public Type getType() {
       return Type.SYMLINK;
     }

     @Override
     public PathFragment getSymlinkTarget() {
       return symlinkTarget;
     }

     @Override
     public boolean equals(Object obj) {
       if (!(obj instanceof SymlinkFileStateValue)) {
         return false;
       }
       SymlinkFileStateValue other = (SymlinkFileStateValue) obj;
       return symlinkTarget.equals(other.symlinkTarget);
     }

     @Override
     public int hashCode() {
       return symlinkTarget.hashCode();
     }

     @Override
     public String prettyPrint() {
       return "symlink to " + symlinkTarget;
     }
   }

   /** Implementation of {@link FileStateValue} for nonexistent files. */
   public static final class NonexistentFileStateValue extends FileStateValue {

     private NonexistentFileStateValue() {
     }

     @Override
     public Type getType() {
       return Type.NONEXISTENT;
     }

     @Override
     public String prettyPrint() {
       return "nonexistent path";
     }

     // This object is normally a singleton, but deserialization produces copies.
     @Override
     public boolean equals(Object obj) {
       return obj instanceof NonexistentFileStateValue;
     }

     @Override
     public int hashCode() {
       return 8765432;
     }
   }
 }
	// Copyright 2014 The Bazel Authors. All rights reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	package com.google.devtools.build.lib.skyframe;

	import com.google.common.annotations.VisibleForTesting;
	import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
	import com.google.devtools.build.lib.util.Preconditions;
	import com.google.devtools.build.lib.util.io.TimestampGranularityMonitor;
	import com.google.devtools.build.lib.vfs.FileStatus;
	import com.google.devtools.build.lib.vfs.FileStatusWithDigest;
	import com.google.devtools.build.lib.vfs.FileStatusWithDigestAdapter;
	import com.google.devtools.build.lib.vfs.Path;
	import com.google.devtools.build.lib.vfs.PathFragment;
	import com.google.devtools.build.lib.vfs.RootedPath;
	import com.google.devtools.build.lib.vfs.Symlinks;
	import com.google.devtools.build.skyframe.LegacySkyKey;
	import com.google.devtools.build.skyframe.SkyKey;
	import com.google.devtools.build.skyframe.SkyValue;
	import java.io.IOException;
	import java.util.Arrays;
	import java.util.Objects;
	import javax.annotation.Nullable;

	/**
	* Encapsulates the filesystem operations needed to get state for a path. This is at least a
	* 'lstat' to determine what type of file the path is.
	* <ul>
	* <li> For a non-existent file, the non existence is noted.
	* <li> For a symlink, the symlink target is noted.
	* <li> For a directory, the existence is noted.
	* <li> For a file, the existence is noted, along with metadata about the file (e.g.
	* file digest). See {@link RegularFileStateValue}.
	* <ul>
	*
	* <p>This class is an implementation detail of {@link FileValue} and should not be used outside of
	* {@link FileFunction}. Instead, {@link FileValue} should be used by consumers that care about
	* files.
	*
	* <p>All subclasses must implement {@link #equals} and {@link #hashCode} properly.
	*/
	@VisibleForTesting
	public abstract class FileStateValue implements SkyValue {

	public static final DirectoryFileStateValue DIRECTORY_FILE_STATE_NODE =
	new DirectoryFileStateValue();
	public static final NonexistentFileStateValue NONEXISTENT_FILE_STATE_NODE =
	new NonexistentFileStateValue();

	/** Type of a path. */
	public enum Type {
	REGULAR_FILE,
	SPECIAL_FILE,
	DIRECTORY,
	SYMLINK,
	NONEXISTENT,
	}

	protected FileStateValue() {
	}

	public static FileStateValue create(RootedPath rootedPath,
	@Nullable TimestampGranularityMonitor tsgm) throws InconsistentFilesystemException,
	IOException {
	Path path = rootedPath.asPath();
	// Stat, but don't throw an exception for the common case of a nonexistent file. This still
	// throws an IOException in case any other IO error is encountered.
	FileStatus stat = path.statIfFound(Symlinks.NOFOLLOW);
	if (stat == null) {
	return NONEXISTENT_FILE_STATE_NODE;
	}
	return createWithStatNoFollow(rootedPath, FileStatusWithDigestAdapter.adapt(stat), tsgm);
	}

	static FileStateValue createWithStatNoFollow(RootedPath rootedPath,
	FileStatusWithDigest statNoFollow, @Nullable TimestampGranularityMonitor tsgm)
	throws InconsistentFilesystemException, IOException {
	Path path = rootedPath.asPath();
	if (statNoFollow.isFile()) {
	return statNoFollow.isSpecialFile()
	? SpecialFileStateValue.fromStat(path.asFragment(), statNoFollow, tsgm)
	: RegularFileStateValue.fromPath(path, statNoFollow, tsgm);
	} else if (statNoFollow.isDirectory()) {
	return DIRECTORY_FILE_STATE_NODE;
	} else if (statNoFollow.isSymbolicLink()) {
	return new SymlinkFileStateValue(path.readSymbolicLinkUnchecked());
	}
	throw new InconsistentFilesystemException("according to stat, existing path " + path + " is "
	+ "neither a file nor directory nor symlink.");
	}

	@VisibleForTesting
	@ThreadSafe
	public static SkyKey key(RootedPath rootedPath) {
	return LegacySkyKey.create(SkyFunctions.FILE_STATE, rootedPath);
	}

	public abstract Type getType();

	PathFragment getSymlinkTarget() {
	throw new IllegalStateException();
	}

	long getSize() {
	throw new IllegalStateException();
	}

	@Nullable
	byte[] getDigest() {
	throw new IllegalStateException();
	}

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

	abstract String prettyPrint();

	/**
	* Implementation of {@link FileStateValue} for regular files that exist.
	*
	* <p>A union of (digest, mtime). We use digests only if a fast digest lookup is available from
	* the filesystem. If not, we fall back to mtime-based digests. This avoids the case where Blaze
	* must read all files involved in the build in order to check for modifications in the case
	* where fast digest lookups are not available.
	*/
	@ThreadSafe
	public static final class RegularFileStateValue extends FileStateValue {
	private final long size;
	// Only needed for empty-file equality-checking. Otherwise is always -1.
	// TODO(bazel-team): Consider getting rid of this special case for empty files.
	private final long mtime;
	@Nullable private final byte[] digest;
	@Nullable private final FileContentsProxy contentsProxy;

	public RegularFileStateValue(long size, long mtime, byte[] digest,
	FileContentsProxy contentsProxy) {
	Preconditions.checkState((digest == null) != (contentsProxy == null));
	this.size = size;
	// mtime is forced to be -1 so that we do not accidentally depend on it for non-empty files,
	// which should only be compared using digests.
	this.mtime = size == 0 ? mtime : -1;
	this.digest = digest;
	this.contentsProxy = contentsProxy;
	}

	/**
	* Create a FileFileStateValue instance corresponding to the given existing file.
	* @param stat must be of type "File". (Not a symlink).
	*/
	private static RegularFileStateValue fromPath(Path path, FileStatusWithDigest stat,
	@Nullable TimestampGranularityMonitor tsgm)
	throws InconsistentFilesystemException {
	Preconditions.checkState(stat.isFile(), path);

	try {
	byte[] digest = tryGetDigest(path, stat);
	if (digest == null) {
	long mtime = stat.getLastModifiedTime();
	// Note that TimestampGranularityMonitor#notifyDependenceOnFileTime is a thread-safe
	// method.
	if (tsgm != null) {
	tsgm.notifyDependenceOnFileTime(path.asFragment(), mtime);
	}
	return new RegularFileStateValue(stat.getSize(), stat.getLastModifiedTime(), null,
	FileContentsProxy.create(stat));
	} else {
	// We are careful here to avoid putting the value ID into FileMetadata if we already have
	// a digest. Arbitrary filesystems may do weird things with the value ID; a digest is more
	// robust.
	return new RegularFileStateValue(stat.getSize(), stat.getLastModifiedTime(), digest, null);
	}
	} catch (IOException e) {
	String errorMessage = e.getMessage() != null
	? "error '" + e.getMessage() + "'" : "an error";
	throw new InconsistentFilesystemException("'stat' said " + path + " is a file but then we "
	+ "later encountered " + errorMessage + " which indicates that " + path + " is no "
	+ "longer a file. Did you delete it during the build?");
	}
	}

	@Nullable
	private static byte[] tryGetDigest(Path path, FileStatusWithDigest stat) throws IOException {
	try {
	byte[] digest = stat.getDigest();
	return digest != null ? digest : path.getFastDigest();
	} catch (IOException ioe) {
	if (!path.isReadable()) {
	return null;
	}
	throw ioe;
	}
	}

	@Override
	public Type getType() {
	return Type.REGULAR_FILE;
	}

	@Override
	public long getSize() {
	return size;
	}

	public long getMtime() {
	return mtime;
	}

	@Override
	@Nullable
	public byte[] getDigest() {
	return digest;
	}

	public FileContentsProxy getContentsProxy() {
	return contentsProxy;
	}

	@Override
	public boolean equals(Object obj) {
	if (obj instanceof RegularFileStateValue) {
	RegularFileStateValue other = (RegularFileStateValue) obj;
	return size == other.size && mtime == other.mtime && Arrays.equals(digest, other.digest)
	&& Objects.equals(contentsProxy, other.contentsProxy);
	}
	return false;
	}

	@Override
	public int hashCode() {
	return Objects.hash(size, mtime, Arrays.hashCode(digest), contentsProxy);
	}

	@Override
	public String prettyPrint() {
	String contents = digest != null
	? String.format("digest of %s", Arrays.toString(digest))
	: contentsProxy.prettyPrint();
	String extra = mtime != -1 ? String.format(" and mtime of %d", mtime) : "";
	return String.format("regular file with size of %d and %s%s", size, contents, extra);
	}
	}

	/** Implementation of {@link FileStateValue} for special files that exist. */
	public static final class SpecialFileStateValue extends FileStateValue {
	private final FileContentsProxy contentsProxy;

	public SpecialFileStateValue(FileContentsProxy contentsProxy) {
	this.contentsProxy = contentsProxy;
	}

	static SpecialFileStateValue fromStat(PathFragment path, FileStatusWithDigest stat,
	@Nullable TimestampGranularityMonitor tsgm) throws IOException {
	long mtime = stat.getLastModifiedTime();
	// Note that TimestampGranularityMonitor#notifyDependenceOnFileTime is a thread-safe
	// method.
	if (tsgm != null) {
	tsgm.notifyDependenceOnFileTime(path, mtime);
	}
	return new SpecialFileStateValue(FileContentsProxy.create(stat));
	}

	@Override
	public Type getType() {
	return Type.SPECIAL_FILE;
	}

	@Override
	long getSize() {
	return 0;
	}

	@Override
	@Nullable
	byte[] getDigest() {
	return null;
	}

	public FileContentsProxy getContentsProxy() {
	return contentsProxy;
	}

	@Override
	public boolean equals(Object obj) {
	if (obj instanceof SpecialFileStateValue) {
	SpecialFileStateValue other = (SpecialFileStateValue) obj;
	return Objects.equals(contentsProxy, other.contentsProxy);
	}
	return false;
	}

	@Override
	public int hashCode() {
	return contentsProxy.hashCode();
	}

	@Override
	public String prettyPrint() {
	return String.format("special file with %s", contentsProxy.prettyPrint());
	}
	}

	/** Implementation of {@link FileStateValue} for directories that exist. */
	public static final class DirectoryFileStateValue extends FileStateValue {

	private DirectoryFileStateValue() {
	}

	@Override
	public Type getType() {
	return Type.DIRECTORY;
	}

	@Override
	public String prettyPrint() {
	return "directory";
	}

	// This object is normally a singleton, but deserialization produces copies.
	@Override
	public boolean equals(Object obj) {
	return obj instanceof DirectoryFileStateValue;
	}

	@Override
	public int hashCode() {
	return 7654321;
	}
	}

	/** Implementation of {@link FileStateValue} for symlinks. */
	public static final class SymlinkFileStateValue extends FileStateValue {

	private final PathFragment symlinkTarget;

	public SymlinkFileStateValue(PathFragment symlinkTarget) {
	this.symlinkTarget = symlinkTarget;
	}

	@Override
	public Type getType() {
	return Type.SYMLINK;
	}

	@Override
	public PathFragment getSymlinkTarget() {
	return symlinkTarget;
	}

	@Override
	public boolean equals(Object obj) {
	if (!(obj instanceof SymlinkFileStateValue)) {
	return false;
	}
	SymlinkFileStateValue other = (SymlinkFileStateValue) obj;
	return symlinkTarget.equals(other.symlinkTarget);
	}

	@Override
	public int hashCode() {
	return symlinkTarget.hashCode();
	}

	@Override
	public String prettyPrint() {
	return "symlink to " + symlinkTarget;
	}
	}

	/** Implementation of {@link FileStateValue} for nonexistent files. */
	public static final class NonexistentFileStateValue extends FileStateValue {

	private NonexistentFileStateValue() {
	}

	@Override
	public Type getType() {
	return Type.NONEXISTENT;
	}

	@Override
	public String prettyPrint() {
	return "nonexistent path";
	}

	// This object is normally a singleton, but deserialization produces copies.
	@Override
	public boolean equals(Object obj) {
	return obj instanceof NonexistentFileStateValue;
	}

	@Override
	public int hashCode() {
	return 8765432;
	}
	}
	}