src/main/java/com/google/devtools/build/lib/vfs/WindowsFileSystem.java - bazel - Git at Google

 // Copyright 2016 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.vfs;

 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.vfs.Path.PathFactory;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.nio.file.Files;
 import java.nio.file.LinkOption;
 import java.nio.file.attribute.DosFileAttributes;
 import java.util.Arrays;
 import java.util.concurrent.TimeUnit;

 /** Jury-rigged file system for Windows. */
 @ThreadSafe
 public class WindowsFileSystem extends JavaIoFileSystem {

   @VisibleForTesting
   enum WindowsPathFactory implements PathFactory {
     INSTANCE {
       @Override
       public Path createRootPath(FileSystem filesystem) {
         return new WindowsPath(filesystem, PathFragment.ROOT_DIR, null);
       }

       @Override
       public Path createChildPath(Path parent, String childName) {
         Preconditions.checkState(parent instanceof WindowsPath);
         return new WindowsPath(parent.getFileSystem(), childName, (WindowsPath) parent);
       }

       @Override
       public TranslatedPath translatePath(Path parent, String child) {
         if (parent != null && parent.isRootDirectory()) {
           // This is a top-level directory. It's either a drive name ("C:" or "c") or some other
           // Unix path (e.g. "/usr").
           //
           // We need to translate it to an absolute Windows path. The correct way would be looking
           // up /etc/mtab to see if any mount point matches the prefix of the path, and change the
           // prefix to the mounted path. Looking up /etc/mtab each time we create a path however
           // would be too expensive so we use a heuristic instead.
           //
           // If the name looks like a volume name ("C:" or "c") then we treat it as such, otherwise
           // we make it relative to UNIX_ROOT, thus "/usr" becomes "C:/tools/msys64/usr".
           //
           // This heuristic ignores other mount points as well as procfs.

           // TODO(bazel-team): get rid of this heuristic and translate paths using /etc/mtab.
           // Figure out how to handle non-top-level mount points (e.g. "/usr/bin" is mounted to
           // "/bin"), which is problematic because Paths are created segment by segment, so
           // individual Path objects don't know they are parts of a mount point path.
           // Another challenge is figuring out how and when to read /etc/mtab. A simple approach is
           // to do it in determineUnixRoot, but then we won't pick up mount changes during the
           // lifetime of the Bazel server process. A correct approach would be to establish a
           // Skyframe FileValue-dependency on it, but it's unclear how this class could request or
           // retrieve Skyframe-computed data.

           if (WindowsPath.isWindowsVolumeName(child)) {
             child = WindowsPath.getDriveLetter((WindowsPath) parent, child) + ":";
           } else {
             Preconditions.checkNotNull(
                 UNIX_ROOT,
                 "Could not determine Unix path root or it is not an absolute Windows path. Set the "
                     + "\"%s\" JVM argument, or export the \"%s\" environment variable for the MSYS "
                     + "bash and have /usr/bin/cygpath installed. Parent is \"%s\", name is \"%s\".",
                 WINDOWS_UNIX_ROOT_JVM_ARG,
                 BAZEL_SH_ENV_VAR,
                 parent,
                 child);
             parent = parent.getRelative(UNIX_ROOT);
           }
         }
         return new TranslatedPath(parent, child);
       }
     };
   }

   private static final class WindowsPath extends Path {

     // The drive letter is '\0' if and only if this Path is the filesystem root "/".
     private char driveLetter;

     private WindowsPath(FileSystem fileSystem) {
       super(fileSystem);
       this.driveLetter = '\0';
     }

     private WindowsPath(FileSystem fileSystem, String name, WindowsPath parent) {
       super(fileSystem, name, parent);
       this.driveLetter = getDriveLetter(parent, name);
     }

     @Override
     protected void buildPathString(StringBuilder result) {
       if (isRootDirectory()) {
         result.append(PathFragment.ROOT_DIR);
       } else {
         if (isTopLevelDirectory()) {
           result.append(driveLetter).append(':').append(PathFragment.SEPARATOR_CHAR);
         } else {
           getParentDirectory().buildPathString(result);
           if (!getParentDirectory().isTopLevelDirectory()) {
             result.append(PathFragment.SEPARATOR_CHAR);
           }
           result.append(getBaseName());
         }
       }
     }

     @Override
     public void reinitializeAfterDeserialization() {
       Preconditions.checkState(
           getParentDirectory().isRootDirectory() || getParentDirectory() instanceof WindowsPath);
       this.driveLetter =
           (getParentDirectory() != null) ? ((WindowsPath) getParentDirectory()).driveLetter : '\0';
     }

     @Override
     public boolean isMaybeRelativeTo(Path ancestorCandidate) {
       Preconditions.checkState(ancestorCandidate instanceof WindowsPath);
       return ancestorCandidate.isRootDirectory()
           || driveLetter == ((WindowsPath) ancestorCandidate).driveLetter;
     }

     @Override
     public boolean isTopLevelDirectory() {
       return isRootDirectory() || getParentDirectory().isRootDirectory();
     }

     @Override
     public PathFragment asFragment() {
       String[] segments = getSegments();
       if (segments.length > 0) {
         // Strip off the first segment that contains the volume name.
         segments = Arrays.copyOfRange(segments, 1, segments.length);
       }

       return new PathFragment(driveLetter, true, segments);
     }

     @Override
     protected Path getRootForRelativePathComputation(PathFragment relative) {
       Path result = this;
       if (relative.isAbsolute()) {
         result = getFileSystem().getRootDirectory();
         if (!relative.windowsVolume().isEmpty()) {
           result = result.getRelative(relative.windowsVolume());
         }
       }
       return result;
     }

     private static boolean isWindowsVolumeName(String name) {
       return (name.length() == 1 || (name.length() == 2 && name.charAt(1) == ':'))
           && Character.isLetter(name.charAt(0));
     }

     private static char getDriveLetter(WindowsPath parent, String name) {
       if (parent == null) {
         return '\0';
       } else {
         if (parent.isRootDirectory()) {
           Preconditions.checkState(
               isWindowsVolumeName(name),
               "top-level directory on Windows must be a drive (name = '%s')",
               name);
           return Character.toUpperCase(name.charAt(0));
         } else {
           return parent.driveLetter;
         }
       }
     }
   }

   private static final String WINDOWS_UNIX_ROOT_JVM_ARG = "bazel.windows_unix_root";
   private static final String BAZEL_SH_ENV_VAR = "BAZEL_SH";

   // Absolute Windows path specifying the root of absolute Unix paths.
   // This is typically the MSYS installation root, e.g. C:\\tools\\msys64
   private static final PathFragment UNIX_ROOT =
       determineUnixRoot(WINDOWS_UNIX_ROOT_JVM_ARG, BAZEL_SH_ENV_VAR);

   public static final LinkOption[] NO_OPTIONS = new LinkOption[0];
   public static final LinkOption[] NO_FOLLOW = new LinkOption[] {LinkOption.NOFOLLOW_LINKS};

   @Override
   protected PathFactory getPathFactory() {
     return WindowsPathFactory.INSTANCE;
   }

   @Override
   public String getFileSystemType(Path path) {
     // TODO(laszlocsomor): implement this properly, i.e. actually query this information from
     // somewhere (java.nio.Filesystem? System.getProperty? implement JNI method and use WinAPI?).
     return "ntfs";
   }

   @Override
   protected void createSymbolicLink(Path linkPath, PathFragment targetFragment) throws IOException {
     // TODO(lberki): Add some JNI to create hard links/junctions instead of calling out to
     // cmd.exe
     File file = getIoFile(linkPath);
     try {
       File targetFile = new File(targetFragment.getPathString());
       if (targetFile.isDirectory()) {
         createDirectoryJunction(targetFile, file);
       } else {
         Files.copy(targetFile.toPath(), file.toPath());
       }
     } catch (java.nio.file.FileAlreadyExistsException e) {
       throw new IOException(linkPath + ERR_FILE_EXISTS);
     } catch (java.nio.file.AccessDeniedException e) {
       throw new IOException(linkPath + ERR_PERMISSION_DENIED);
     } catch (java.nio.file.NoSuchFileException e) {
       throw new FileNotFoundException(linkPath + ERR_NO_SUCH_FILE_OR_DIR);
     }
   }

   @Override
   public boolean supportsSymbolicLinksNatively() {
     return false;
   }

   @Override
   public boolean isFilePathCaseSensitive() {
     return false;
   }

   private void createDirectoryJunction(File sourceDirectory, File targetPath) throws IOException {
     StringBuilder cl = new StringBuilder("cmd.exe /c ");
     cl.append("mklink /J ");
     cl.append('"');
     cl.append(targetPath.getAbsolutePath());
     cl.append('"');
     cl.append(' ');
     cl.append('"');
     cl.append(sourceDirectory.getAbsolutePath());
     cl.append('"');
     Process process = Runtime.getRuntime().exec(cl.toString());
     try {
       process.waitFor();
       if (process.exitValue() != 0) {
         throw new IOException("Command failed " + cl);
       }
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
       throw new IOException("Command failed ", e);
     }
   }

   @Override
   protected boolean fileIsSymbolicLink(File file) {
     try {
       if (isJunction(file)) {
         return true;
       }
     } catch (IOException e) {
       // Did not work, try in another way
     }
     return super.fileIsSymbolicLink(file);
   }

   public static LinkOption[] symlinkOpts(boolean followSymlinks) {
     return followSymlinks ? NO_OPTIONS : NO_FOLLOW;
   }

   @Override
   protected FileStatus stat(Path path, boolean followSymlinks) throws IOException {
     File file = getIoFile(path);
     final DosFileAttributes attributes;
     try {
       attributes = getAttribs(file, followSymlinks);
     } catch (IOException e) {
       throw new FileNotFoundException(path + ERR_NO_SUCH_FILE_OR_DIR);
     }

     final boolean isSymbolicLink = !followSymlinks && fileIsSymbolicLink(file);
     FileStatus status =
         new FileStatus() {
           @Override
           public boolean isFile() {
             return attributes.isRegularFile() || (isSpecialFile() && !isDirectory());
           }

           @Override
           public boolean isSpecialFile() {
             return attributes.isOther();
           }

           @Override
           public boolean isDirectory() {
             return attributes.isDirectory();
           }

           @Override
           public boolean isSymbolicLink() {
             return isSymbolicLink;
           }

           @Override
           public long getSize() throws IOException {
             return attributes.size();
           }

           @Override
           public long getLastModifiedTime() throws IOException {
             return attributes.lastModifiedTime().toMillis();
           }

           @Override
           public long getLastChangeTime() {
             // This is the best we can do with Java NIO...
             return attributes.lastModifiedTime().toMillis();
           }

           @Override
           public long getNodeId() {
             // TODO(bazel-team): Consider making use of attributes.fileKey().
             return -1;
           }
         };

     return status;
   }

   @Override
   protected boolean isDirectory(Path path, boolean followSymlinks) {
     if (!followSymlinks) {
       try {
         if (isJunction(getIoFile(path))) {
           return false;
         }
       } catch (IOException e) {
         return false;
       }
     }
     return super.isDirectory(path, followSymlinks);
   }

   /**
    * Returns true if the path refers to a directory junction, directory symlink, or regular symlink.
    *
    * <p>Directory junctions are symbolic links created with "mklink /J" where the target is a
    * directory or another directory junction. Directory junctions can be created without any user
    * privileges.
    *
    * <p>Directory symlinks are symbolic links created with "mklink /D" where the target is a
    * directory or another directory symlink. Note that directory symlinks can only be created by
    * Administrators.
    *
    * <p>Normal symlinks are symbolic links created with "mklink". Normal symlinks should not point
    * at directories, because even though "mklink" can create the link, it will not be a functional
    * one (the linked directory's contents cannot be listed). Only Administrators may create regular
    * symlinks.
    *
    * <p>This method returns true for all three types as long as their target is a directory (even if
    * they are dangling), though only directory junctions and directory symlinks are useful.
    */
   // TODO(laszlocsomor): fix https://github.com/bazelbuild/bazel/issues/1735 and use the JNI method
   // in WindowsFileOperations.
   @VisibleForTesting
   static boolean isJunction(File file) throws IOException {
     if (Files.exists(file.toPath(), symlinkOpts(/* followSymlinks */ false))) {
       DosFileAttributes attributes = getAttribs(file, /* followSymlinks */ false);

       if (attributes.isRegularFile()) {
         return false;
       }

       if (attributes.isDirectory()) {
         return attributes.isOther();
       } else {
         return attributes.isSymbolicLink();
       }
     }
     return false;
   }

   private static DosFileAttributes getAttribs(File file, boolean followSymlinks)
       throws IOException {
     return Files.readAttributes(
         file.toPath(), DosFileAttributes.class, symlinkOpts(followSymlinks));
   }

   private static PathFragment determineUnixRoot(String jvmArgName, String bazelShEnvVar) {
     // Get the path from a JVM argument, if specified.
     String path = System.getProperty(jvmArgName);

     if (path == null || path.isEmpty()) {
       path = "";

       // Fall back to executing cygpath.
       String bash = System.getenv(bazelShEnvVar);
       Process process = null;
       try {
         process = Runtime.getRuntime().exec("cmd.exe /C " + bash + " -c \"/usr/bin/cygpath -m /\"");

         // Wait 3 seconds max, that should be enough to run this command.
         process.waitFor(3, TimeUnit.SECONDS);

         if (process.exitValue() == 0) {
           path = readAll(process.getInputStream());
         } else {
           System.err.print(
               String.format(
                   "ERROR: %s (exit code: %d)%n",
                   readAll(process.getErrorStream()), process.exitValue()));
         }
       } catch (InterruptedException | IOException e) {
         // Silently ignore failure. Either MSYS is installed at a different location, or not
         // installed at all, or some error occurred. We can't do anything anymore but throw an
         // exception if someone tries to create a Path from an absolute Unix path.
         return null;
       }
     }

     path = path.trim();
     PathFragment result = new PathFragment(path);
     if (path.isEmpty() || result.getDriveLetter() == '\0' || !result.isAbsolute()) {
       return null;
     } else {
       return result;
     }
   }

   private static String readAll(InputStream s) throws IOException {
     String result = "";
     int len;
     char[] buf = new char[4096];
     try (InputStreamReader r = new InputStreamReader(s)) {
       while ((len = r.read(buf)) > 0) {
         result += new String(buf, 0, len);
       }
     }
     return result;
   }
 }
	// Copyright 2016 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.vfs;

	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.vfs.Path.PathFactory;
	import java.io.File;
	import java.io.FileNotFoundException;
	import java.io.IOException;
	import java.io.InputStream;
	import java.io.InputStreamReader;
	import java.nio.file.Files;
	import java.nio.file.LinkOption;
	import java.nio.file.attribute.DosFileAttributes;
	import java.util.Arrays;
	import java.util.concurrent.TimeUnit;

	/** Jury-rigged file system for Windows. */
	@ThreadSafe
	public class WindowsFileSystem extends JavaIoFileSystem {

	@VisibleForTesting
	enum WindowsPathFactory implements PathFactory {
	INSTANCE {
	@Override
	public Path createRootPath(FileSystem filesystem) {
	return new WindowsPath(filesystem, PathFragment.ROOT_DIR, null);
	}

	@Override
	public Path createChildPath(Path parent, String childName) {
	Preconditions.checkState(parent instanceof WindowsPath);
	return new WindowsPath(parent.getFileSystem(), childName, (WindowsPath) parent);
	}

	@Override
	public TranslatedPath translatePath(Path parent, String child) {
	if (parent != null && parent.isRootDirectory()) {
	// This is a top-level directory. It's either a drive name ("C:" or "c") or some other
	// Unix path (e.g. "/usr").
	//
	// We need to translate it to an absolute Windows path. The correct way would be looking
	// up /etc/mtab to see if any mount point matches the prefix of the path, and change the
	// prefix to the mounted path. Looking up /etc/mtab each time we create a path however
	// would be too expensive so we use a heuristic instead.
	//
	// If the name looks like a volume name ("C:" or "c") then we treat it as such, otherwise
	// we make it relative to UNIX_ROOT, thus "/usr" becomes "C:/tools/msys64/usr".
	//
	// This heuristic ignores other mount points as well as procfs.

	// TODO(bazel-team): get rid of this heuristic and translate paths using /etc/mtab.
	// Figure out how to handle non-top-level mount points (e.g. "/usr/bin" is mounted to
	// "/bin"), which is problematic because Paths are created segment by segment, so
	// individual Path objects don't know they are parts of a mount point path.
	// Another challenge is figuring out how and when to read /etc/mtab. A simple approach is
	// to do it in determineUnixRoot, but then we won't pick up mount changes during the
	// lifetime of the Bazel server process. A correct approach would be to establish a
	// Skyframe FileValue-dependency on it, but it's unclear how this class could request or
	// retrieve Skyframe-computed data.

	if (WindowsPath.isWindowsVolumeName(child)) {
	child = WindowsPath.getDriveLetter((WindowsPath) parent, child) + ":";
	} else {
	Preconditions.checkNotNull(
	UNIX_ROOT,
	"Could not determine Unix path root or it is not an absolute Windows path. Set the "
	+ "\"%s\" JVM argument, or export the \"%s\" environment variable for the MSYS "
	+ "bash and have /usr/bin/cygpath installed. Parent is \"%s\", name is \"%s\".",
	WINDOWS_UNIX_ROOT_JVM_ARG,
	BAZEL_SH_ENV_VAR,
	parent,
	child);
	parent = parent.getRelative(UNIX_ROOT);
	}
	}
	return new TranslatedPath(parent, child);
	}
	};
	}

	private static final class WindowsPath extends Path {

	// The drive letter is '\0' if and only if this Path is the filesystem root "/".
	private char driveLetter;

	private WindowsPath(FileSystem fileSystem) {
	super(fileSystem);
	this.driveLetter = '\0';
	}

	private WindowsPath(FileSystem fileSystem, String name, WindowsPath parent) {
	super(fileSystem, name, parent);
	this.driveLetter = getDriveLetter(parent, name);
	}

	@Override
	protected void buildPathString(StringBuilder result) {
	if (isRootDirectory()) {
	result.append(PathFragment.ROOT_DIR);
	} else {
	if (isTopLevelDirectory()) {
	result.append(driveLetter).append(':').append(PathFragment.SEPARATOR_CHAR);
	} else {
	getParentDirectory().buildPathString(result);
	if (!getParentDirectory().isTopLevelDirectory()) {
	result.append(PathFragment.SEPARATOR_CHAR);
	}
	result.append(getBaseName());
	}
	}
	}

	@Override
	public void reinitializeAfterDeserialization() {
	Preconditions.checkState(
	getParentDirectory().isRootDirectory() \|\| getParentDirectory() instanceof WindowsPath);
	this.driveLetter =
	(getParentDirectory() != null) ? ((WindowsPath) getParentDirectory()).driveLetter : '\0';
	}

	@Override
	public boolean isMaybeRelativeTo(Path ancestorCandidate) {
	Preconditions.checkState(ancestorCandidate instanceof WindowsPath);
	return ancestorCandidate.isRootDirectory()
	\|\| driveLetter == ((WindowsPath) ancestorCandidate).driveLetter;
	}

	@Override
	public boolean isTopLevelDirectory() {
	return isRootDirectory() \|\| getParentDirectory().isRootDirectory();
	}

	@Override
	public PathFragment asFragment() {
	String[] segments = getSegments();
	if (segments.length > 0) {
	// Strip off the first segment that contains the volume name.
	segments = Arrays.copyOfRange(segments, 1, segments.length);
	}

	return new PathFragment(driveLetter, true, segments);
	}

	@Override
	protected Path getRootForRelativePathComputation(PathFragment relative) {
	Path result = this;
	if (relative.isAbsolute()) {
	result = getFileSystem().getRootDirectory();
	if (!relative.windowsVolume().isEmpty()) {
	result = result.getRelative(relative.windowsVolume());
	}
	}
	return result;
	}

	private static boolean isWindowsVolumeName(String name) {
	return (name.length() == 1 \|\| (name.length() == 2 && name.charAt(1) == ':'))
	&& Character.isLetter(name.charAt(0));
	}

	private static char getDriveLetter(WindowsPath parent, String name) {
	if (parent == null) {
	return '\0';
	} else {
	if (parent.isRootDirectory()) {
	Preconditions.checkState(
	isWindowsVolumeName(name),
	"top-level directory on Windows must be a drive (name = '%s')",
	name);
	return Character.toUpperCase(name.charAt(0));
	} else {
	return parent.driveLetter;
	}
	}
	}
	}

	private static final String WINDOWS_UNIX_ROOT_JVM_ARG = "bazel.windows_unix_root";
	private static final String BAZEL_SH_ENV_VAR = "BAZEL_SH";

	// Absolute Windows path specifying the root of absolute Unix paths.
	// This is typically the MSYS installation root, e.g. C:\\tools\\msys64
	private static final PathFragment UNIX_ROOT =
	determineUnixRoot(WINDOWS_UNIX_ROOT_JVM_ARG, BAZEL_SH_ENV_VAR);

	public static final LinkOption[] NO_OPTIONS = new LinkOption[0];
	public static final LinkOption[] NO_FOLLOW = new LinkOption[] {LinkOption.NOFOLLOW_LINKS};

	@Override
	protected PathFactory getPathFactory() {
	return WindowsPathFactory.INSTANCE;
	}

	@Override
	public String getFileSystemType(Path path) {
	// TODO(laszlocsomor): implement this properly, i.e. actually query this information from
	// somewhere (java.nio.Filesystem? System.getProperty? implement JNI method and use WinAPI?).
	return "ntfs";
	}

	@Override
	protected void createSymbolicLink(Path linkPath, PathFragment targetFragment) throws IOException {
	// TODO(lberki): Add some JNI to create hard links/junctions instead of calling out to
	// cmd.exe
	File file = getIoFile(linkPath);
	try {
	File targetFile = new File(targetFragment.getPathString());
	if (targetFile.isDirectory()) {
	createDirectoryJunction(targetFile, file);
	} else {
	Files.copy(targetFile.toPath(), file.toPath());
	}
	} catch (java.nio.file.FileAlreadyExistsException e) {
	throw new IOException(linkPath + ERR_FILE_EXISTS);
	} catch (java.nio.file.AccessDeniedException e) {
	throw new IOException(linkPath + ERR_PERMISSION_DENIED);
	} catch (java.nio.file.NoSuchFileException e) {
	throw new FileNotFoundException(linkPath + ERR_NO_SUCH_FILE_OR_DIR);
	}
	}

	@Override
	public boolean supportsSymbolicLinksNatively() {
	return false;
	}

	@Override
	public boolean isFilePathCaseSensitive() {
	return false;
	}

	private void createDirectoryJunction(File sourceDirectory, File targetPath) throws IOException {
	StringBuilder cl = new StringBuilder("cmd.exe /c ");
	cl.append("mklink /J ");
	cl.append('"');
	cl.append(targetPath.getAbsolutePath());
	cl.append('"');
	cl.append(' ');
	cl.append('"');
	cl.append(sourceDirectory.getAbsolutePath());
	cl.append('"');
	Process process = Runtime.getRuntime().exec(cl.toString());
	try {
	process.waitFor();
	if (process.exitValue() != 0) {
	throw new IOException("Command failed " + cl);
	}
	} catch (InterruptedException e) {
	Thread.currentThread().interrupt();
	throw new IOException("Command failed ", e);
	}
	}

	@Override
	protected boolean fileIsSymbolicLink(File file) {
	try {
	if (isJunction(file)) {
	return true;
	}
	} catch (IOException e) {
	// Did not work, try in another way
	}
	return super.fileIsSymbolicLink(file);
	}

	public static LinkOption[] symlinkOpts(boolean followSymlinks) {
	return followSymlinks ? NO_OPTIONS : NO_FOLLOW;
	}

	@Override
	protected FileStatus stat(Path path, boolean followSymlinks) throws IOException {
	File file = getIoFile(path);
	final DosFileAttributes attributes;
	try {
	attributes = getAttribs(file, followSymlinks);
	} catch (IOException e) {
	throw new FileNotFoundException(path + ERR_NO_SUCH_FILE_OR_DIR);
	}

	final boolean isSymbolicLink = !followSymlinks && fileIsSymbolicLink(file);
	FileStatus status =
	new FileStatus() {
	@Override
	public boolean isFile() {
	return attributes.isRegularFile() \|\| (isSpecialFile() && !isDirectory());
	}

	@Override
	public boolean isSpecialFile() {
	return attributes.isOther();
	}

	@Override
	public boolean isDirectory() {
	return attributes.isDirectory();
	}

	@Override
	public boolean isSymbolicLink() {
	return isSymbolicLink;
	}

	@Override
	public long getSize() throws IOException {
	return attributes.size();
	}

	@Override
	public long getLastModifiedTime() throws IOException {
	return attributes.lastModifiedTime().toMillis();
	}

	@Override
	public long getLastChangeTime() {
	// This is the best we can do with Java NIO...
	return attributes.lastModifiedTime().toMillis();
	}

	@Override
	public long getNodeId() {
	// TODO(bazel-team): Consider making use of attributes.fileKey().
	return -1;
	}
	};

	return status;
	}

	@Override
	protected boolean isDirectory(Path path, boolean followSymlinks) {
	if (!followSymlinks) {
	try {
	if (isJunction(getIoFile(path))) {
	return false;
	}
	} catch (IOException e) {
	return false;
	}
	}
	return super.isDirectory(path, followSymlinks);
	}

	/**
	* Returns true if the path refers to a directory junction, directory symlink, or regular symlink.
	*
	* <p>Directory junctions are symbolic links created with "mklink /J" where the target is a
	* directory or another directory junction. Directory junctions can be created without any user
	* privileges.
	*
	* <p>Directory symlinks are symbolic links created with "mklink /D" where the target is a
	* directory or another directory symlink. Note that directory symlinks can only be created by
	* Administrators.
	*
	* <p>Normal symlinks are symbolic links created with "mklink". Normal symlinks should not point
	* at directories, because even though "mklink" can create the link, it will not be a functional
	* one (the linked directory's contents cannot be listed). Only Administrators may create regular
	* symlinks.
	*
	* <p>This method returns true for all three types as long as their target is a directory (even if
	* they are dangling), though only directory junctions and directory symlinks are useful.
	*/
	// TODO(laszlocsomor): fix https://github.com/bazelbuild/bazel/issues/1735 and use the JNI method
	// in WindowsFileOperations.
	@VisibleForTesting
	static boolean isJunction(File file) throws IOException {
	if (Files.exists(file.toPath(), symlinkOpts(/* followSymlinks */ false))) {
	DosFileAttributes attributes = getAttribs(file, /* followSymlinks */ false);

	if (attributes.isRegularFile()) {
	return false;
	}

	if (attributes.isDirectory()) {
	return attributes.isOther();
	} else {
	return attributes.isSymbolicLink();
	}
	}
	return false;
	}

	private static DosFileAttributes getAttribs(File file, boolean followSymlinks)
	throws IOException {
	return Files.readAttributes(
	file.toPath(), DosFileAttributes.class, symlinkOpts(followSymlinks));
	}

	private static PathFragment determineUnixRoot(String jvmArgName, String bazelShEnvVar) {
	// Get the path from a JVM argument, if specified.
	String path = System.getProperty(jvmArgName);

	if (path == null \|\| path.isEmpty()) {
	path = "";

	// Fall back to executing cygpath.
	String bash = System.getenv(bazelShEnvVar);
	Process process = null;
	try {
	process = Runtime.getRuntime().exec("cmd.exe /C " + bash + " -c \"/usr/bin/cygpath -m /\"");

	// Wait 3 seconds max, that should be enough to run this command.
	process.waitFor(3, TimeUnit.SECONDS);

	if (process.exitValue() == 0) {
	path = readAll(process.getInputStream());
	} else {
	System.err.print(
	String.format(
	"ERROR: %s (exit code: %d)%n",
	readAll(process.getErrorStream()), process.exitValue()));
	}
	} catch (InterruptedException \| IOException e) {
	// Silently ignore failure. Either MSYS is installed at a different location, or not
	// installed at all, or some error occurred. We can't do anything anymore but throw an
	// exception if someone tries to create a Path from an absolute Unix path.
	return null;
	}
	}

	path = path.trim();
	PathFragment result = new PathFragment(path);
	if (path.isEmpty() \|\| result.getDriveLetter() == '\0' \|\| !result.isAbsolute()) {
	return null;
	} else {
	return result;
	}
	}

	private static String readAll(InputStream s) throws IOException {
	String result = "";
	int len;
	char[] buf = new char[4096];
	try (InputStreamReader r = new InputStreamReader(s)) {
	while ((len = r.read(buf)) > 0) {
	result += new String(buf, 0, len);
	}
	}
	return result;
	}
	}