[9.0.0] Compensate for Windows filesystems lacking junction support

src/main/java/com/google/devtools/build/lib/windows/WindowsFileOperations.java

@@ -70,6 +70,7 @@ private WindowsFileOperations() {
   private static final int CREATE_JUNCTION_ALREADY_EXISTS_BUT_NOT_A_JUNCTION = 4;
   private static final int CREATE_JUNCTION_ACCESS_DENIED = 5;
   private static final int CREATE_JUNCTION_DISAPPEARED = 6;
+  private static final int CREATE_JUNCTION_NOT_SUPPORTED = 7;
 
   // Keep CREATE_SYMLINK_* values in sync with src/main/native/windows/file.h.
   private static final int CREATE_SYMLINK_SUCCESS = 0;
@@ -172,6 +173,9 @@ public static void createJunction(String name, String target) throws IOException
       case CREATE_JUNCTION_DISAPPEARED:
         error[0] = "the junction's path got modified unexpectedly";
         break;
+      case CREATE_JUNCTION_NOT_SUPPORTED:
+        error[0] = "filesystem does not support junctions";
+        break;
       default:
         // This is CREATE_JUNCTION_ERROR (1). The JNI code puts a custom message in 'error[0]'.
         break;

src/main/native/windows/file.cc

@@ -456,6 +456,11 @@ int CreateJunction(const wstring& junction_name, const wstring& junction_target,
       if (err == ERROR_DIR_NOT_EMPTY) {
         return CreateJunctionResult::kAlreadyExistsButNotJunction;
       }
+      // ERROR_INVALID_FUNCTION indicates the filesystem doesn't support
+      // junction/reparse point operations (e.g., virtiofs).
+      if (err == ERROR_INVALID_FUNCTION) {
+        return CreateJunctionResult::kNotSupported;
+      }
       // Some unknown error occurred.
       if (error) {
         *error = MakeErrorMessage(WSTR(__FILE__), __LINE__, L"DeviceIoControl",
@@ -587,6 +592,11 @@ int ReadSymlinkOrJunction(const wstring& path, wstring* result,
     if (err == ERROR_NOT_A_REPARSE_POINT) {
       return ReadSymlinkOrJunctionResult::kNotALink;
     }
+    // ERROR_INVALID_FUNCTION indicates the filesystem doesn't support
+    // reparse point operations (e.g., virtiofs). Treat as not a link.
+    if (err == ERROR_INVALID_FUNCTION) {
+      return ReadSymlinkOrJunctionResult::kNotALink;
+    }
 
     // Some unknown error occurred.
     if (error) {

src/main/native/windows/file.h

@@ -113,6 +113,7 @@ struct CreateJunctionResult {
     kAlreadyExistsButNotJunction = 4,
     kAccessDenied = 5,
     kDisappeared = 6,
+    kNotSupported = 7,
   };
 };