Windows,JNI: more robust nativeCreateJunction

Rewrite the CreateJunction function in the Windows
JNI library.

The new implementation's improvements:

- succeeds if the junction already exists with the
  desired target; hopefully this will fix issue
  https://github.com/bazelbuild/bazel/issues/5433

- tolerant to concurrent filesystem modifications,
  e.g. if the junction's path suddenly disappears,
  the function reports the error correctly

Fixes https://github.com/bazelbuild/bazel/issues/5433

Change-Id: I58a2314a00f6edaa7c36c35ba54616168b44eb7d

Closes #5528.

Change-Id: I9f5dc9237b70a433d0d8c2578a826de3d462d110
PiperOrigin-RevId: 203744515

1 files changed, 35 insertions, 2 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java b/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java
index 6a16ab8aab..229c207e91 100644
--- a/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java
+++ b/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java
@@ -49,6 +49,16 @@ public class WindowsFileOperations {
   private static final int IS_JUNCTION_NO = 1;
   private static final int IS_JUNCTION_ERROR = 2;
 
+  // Keep CREATE_JUNCTION_* values in sync with src/main/native/windows/file.cc.
+  private static final int CREATE_JUNCTION_SUCCESS = 0;
+  private static final int CREATE_JUNCTION_ERROR = 1;
+  private static final int CREATE_JUNCTION_TARGET_NAME_TOO_LONG = 2;
+  private static final int CREATE_JUNCTION_PARENT_MISSING = 3;
+  private static final int CREATE_JUNCTION_ALREADY_EXISTS_WITH_DIFFERENT_TARGET = 4;
+  private static final int CREATE_JUNCTION_ALREADY_EXISTS_BUT_NOT_A_JUNCTION = 5;
+  private static final int CREATE_JUNCTION_ACCESS_DENIED = 6;
+  private static final int CREATE_JUNCTION_DISAPPEARED = 7;
+
   // Keep DELETE_PATH_* values in sync with src/main/native/windows/file.cc.
   private static final int DELETE_PATH_SUCCESS = 0;
   private static final int DELETE_PATH_DOES_NOT_EXIST = 1;
@@ -60,7 +70,7 @@ public class WindowsFileOperations {
 
   private static native boolean nativeGetLongPath(String path, String[] result, String[] error);
 
-  private static native boolean nativeCreateJunction(String name, String target, String[] error);
+  private static native int nativeCreateJunction(String name, String target, String[] error);
 
   private static native int nativeDeletePath(String path, String[] error);
 
@@ -125,7 +135,30 @@ public class WindowsFileOperations {
   public static void createJunction(String name, String target) throws IOException {
     WindowsJniLoader.loadJni();
     String[] error = new String[] {null};
-    if (!nativeCreateJunction(name.replace('/', '\\'), target.replace('/', '\\'), error)) {
+    int result = nativeCreateJunction(name.replace('/', '\\'), target.replace('/', '\\'), error);
+    if (result != CREATE_JUNCTION_SUCCESS) {
+      switch (result) {
+        case CREATE_JUNCTION_TARGET_NAME_TOO_LONG:
+          error[0] = "target name is too long";
+          break;
+        case CREATE_JUNCTION_PARENT_MISSING:
+          error[0] = "a parent directory is missing";
+          break;
+        case CREATE_JUNCTION_ALREADY_EXISTS_WITH_DIFFERENT_TARGET:
+          error[0] = "junction already exists with different target";
+          break;
+        case CREATE_JUNCTION_ALREADY_EXISTS_BUT_NOT_A_JUNCTION:
+          error[0] = "a file or directory already exists at the junction's path";
+          break;
+        case CREATE_JUNCTION_ACCESS_DENIED:
+          error[0] = "access is denied";
+          break;
+        case CREATE_JUNCTION_DISAPPEARED:
+          error[0] = "the junction's path got modified unexpectedly";
+          break;
+        default:
+          break;
+      }
       throw new IOException(
           String.format("Cannot create junction (name=%s, target=%s): %s", name, target, error[0]));
     }