--- a/mercurial/vfs.py	Mon Jan 20 12:41:20 2025 +0100
+++ b/mercurial/vfs.py	Wed Jan 29 02:17:33 2025 +0100
@@ -25,6 +25,7 @@
     List,
     MutableMapping,
     Optional,
+    Set,
     Tuple,
     Type,
     TypeVar,
@@ -86,6 +87,9 @@
     # by the Rust code
     rust_compatible = True
 
+    # createmode is always available on subclasses
+    createmode: int
+
     # TODO: type return, which is util.posixfile wrapped by a proxy
     @abc.abstractmethod
     def __call__(self, path: bytes, mode: bytes = b'rb', **kwargs) -> Any:
@@ -456,6 +460,23 @@
     def register_file(self, path: bytes) -> None:
         """generic hook point to lets fncache steer its stew"""
 
+    def prepare_streamed_file(
+        self, path: bytes, known_directories: Set[bytes]
+    ) -> None:
+        """make sure we are ready to write a file from a stream clone
+
+        The "known_directories" variable is here to avoid trying to create the
+        same directories over and over during a stream clone. It will be
+        updated by this function.
+        """
+        self._auditpath(path, b'wb')
+        self.register_file(path)
+        real_path = self.join(path)
+        dirname, basename = util.split(real_path)
+        if dirname not in known_directories:
+            util.makedirs(dirname, self.createmode, True)
+            known_directories.add(dirname)
+
 
 class vfs(abstractvfs):
     """Operate files relative to a base directory