Add a (working) windows compatibility mode that makes Bazel create hardlinks for links to writable files.

Curiously enough, the native Unix JNI wrapper already had a function for link(), but it wasn't on the Java interface.

build-runfiles is also updated accordingly.

--
MOS_MIGRATED_REVID=113029168

3 files changed, 27 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java b/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java
index b557a6a08a..9534f5c591 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java
@@ -27,8 +27,11 @@ import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.shell.CommandException;
 import com.google.devtools.build.lib.util.CommandBuilder;
 import com.google.devtools.build.lib.util.OsUtils;
+import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
+import com.google.devtools.build.lib.vfs.UnixFileSystem;
+import com.google.devtools.build.lib.vfs.UnixFileSystem.SymlinkStrategy;
 
 import java.util.List;
 
@@ -130,6 +133,12 @@ public final class SymlinkTreeHelper {
       args.add("--use_metadata");
     }
 
+    FileSystem fs = execRoot.getFileSystem();
+    if (fs instanceof UnixFileSystem
+        && ((UnixFileSystem) fs).getSymlinkStrategy() == SymlinkStrategy.WINDOWS_COMPATIBLE) {
+      args.add("--windows_compatible");
+    }
+
     args.add(inputManifest.getPathString());
     args.add(symlinkTreeRoot.getPathString());
 
diff --git a/src/main/java/com/google/devtools/build/lib/unix/FilesystemUtils.java b/src/main/java/com/google/devtools/build/lib/unix/FilesystemUtils.java
index 2e062a72bb..eab24a525d 100644
--- a/src/main/java/com/google/devtools/build/lib/unix/FilesystemUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/unix/FilesystemUtils.java
@@ -167,6 +167,16 @@ public final class FilesystemUtils {
       throws IOException;
 
   /**
+   * Native wrapper around POSIX link(2) syscall.
+   *
+   * @param oldpath the file to link to
+   * @param newpath the new path for the link
+   * @throws IOException iff the link() syscall failed.
+   */
+  public static native void link(String oldpath, String newpath)
+    throws IOException;
+
+  /**
    * Native wrapper around POSIX stat(2) syscall.
    *
    * @param path the file to stat.
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/UnixFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/UnixFileSystem.java
index c0d41bd9c1..ee6af3fb39 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/UnixFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/UnixFileSystem.java
@@ -374,7 +374,10 @@ public class UnixFileSystem extends AbstractFileSystemWithCustomStat {
       throws IOException {
     SymlinkImplementation strategy = computeSymlinkImplementation(linkPath, targetFragment);
     switch (strategy) {
-      case HARDLINK:  // TBD, fallthrough for now
+      case HARDLINK:
+        FilesystemUtils.link(targetFragment.toString(), linkPath.toString());
+        break;
+
       case JUNCTION:  // Junctions are emulated on Linux with symlinks, fall through
       case SYMLINK:
         synchronized (linkPath) {
@@ -492,6 +495,10 @@ public class UnixFileSystem extends AbstractFileSystemWithCustomStat {
         "Target is a non-writable file", linkPath, targetFragment);
   }
 
+  public SymlinkStrategy getSymlinkStrategy() {
+    return symlinkStrategy;
+  }
+
   @Override
   protected PathFragment readSymbolicLink(Path path) throws IOException {
     // Note that the default implementation of readSymbolicLinkUnchecked calls this method and thus