Windows: add a Java-native isJunction method

Also add tests for WindowsFileSystem and some for
WindowsFileOperations, so we test both the
JNI-based and Java-native isJunction function, as
well as handling of dangling symlinks/junctions.

Having a Java-native version of this method means
we don't need to use windows_jni.dll for any tests
or for bootstrapping.

This change could help with
https://github.com/bazelbuild/bazel/issues/1735

--
MOS_MIGRATED_REVID=132556440

1 files changed, 89 insertions, 55 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/vfs/WindowsFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/WindowsFileSystem.java
index 325176cb66..da04735831 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/WindowsFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/WindowsFileSystem.java
@@ -13,6 +13,7 @@
 // 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 java.io.File;
 import java.io.FileNotFoundException;
@@ -20,19 +21,17 @@ import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.LinkOption;
 import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.DosFileAttributes;
 
-/**
- * Jury-rigged file system for Windows.
- */
+/** Jury-rigged file system for Windows. */
 @ThreadSafe
 public class WindowsFileSystem extends JavaIoFileSystem {
 
   public static final LinkOption[] NO_OPTIONS = new LinkOption[0];
-  public static final LinkOption[] NO_FOLLOW = new LinkOption[]{LinkOption.NOFOLLOW_LINKS};
+  public static final LinkOption[] NO_FOLLOW = new LinkOption[] {LinkOption.NOFOLLOW_LINKS};
 
   @Override
-  protected void createSymbolicLink(Path linkPath, PathFragment targetFragment)
-      throws IOException {
+  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);
@@ -96,7 +95,7 @@ public class WindowsFileSystem extends JavaIoFileSystem {
     return super.fileIsSymbolicLink(file);
   }
 
-  private LinkOption[] linkOpts(boolean followSymlinks) {
+  public static LinkOption[] symlinkOpts(boolean followSymlinks) {
     return followSymlinks ? NO_OPTIONS : NO_FOLLOW;
   }
 
@@ -105,56 +104,58 @@ public class WindowsFileSystem extends JavaIoFileSystem {
     File file = getIoFile(path);
     final BasicFileAttributes attributes;
     try {
-      attributes = Files.readAttributes(
-          file.toPath(), BasicFileAttributes.class, linkOpts(followSymlinks));
+      attributes =
+          Files.readAttributes(
+              file.toPath(), BasicFileAttributes.class, symlinkOpts(followSymlinks));
     } catch (java.nio.file.FileSystemException 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;
-      }
-    };
+    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;
   }
@@ -173,10 +174,43 @@ public class WindowsFileSystem extends JavaIoFileSystem {
     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.
-  private static boolean isJunction(java.nio.file.Path p) throws IOException {
-    // Jury-rigged
-    return p.compareTo(p.toRealPath()) != 0;
+  @VisibleForTesting
+  static boolean isJunction(java.nio.file.Path p) throws IOException {
+    if (Files.exists(p, symlinkOpts(/* followSymlinks */ false))) {
+      DosFileAttributes attributes =
+          Files.readAttributes(p, DosFileAttributes.class, symlinkOpts(/* followSymlinks */ false));
+
+      if (attributes.isRegularFile()) {
+        return false;
+      }
+
+      if (attributes.isDirectory()) {
+        return attributes.isOther();
+      } else {
+        return attributes.isSymbolicLink();
+      }
+    }
+    return false;
   }
 }