Fix Incomplete File Not found on windows systems (#3247)

* Fix incomplete path

Fixing mixing incomplete path. Paths longer than 256 characters in Windows require modification to be usable. The previous solutions didn't consider paths with \\?\\ already on the path and did not consider paths with fewer than 256 characters, but adding etag and incomplete made the path longer.

* Fix incomplete path error

Paths with already the prefix \\?\ should not incorporate it again

* Apply suggestions from code review

* Apply style fixes

---------

Co-authored-by: Lucain <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

src/huggingface_hub/_local_folder.py

@@ -86,7 +86,13 @@ class LocalDownloadFilePaths:
 
     def incomplete_path(self, etag: str) -> Path:
         """Return the path where a file will be temporarily downloaded before being moved to `file_path`."""
-        return self.metadata_path.parent / f"{_short_hash(self.metadata_path.name)}.{etag}.incomplete"
+        path = self.metadata_path.parent / f"{_short_hash(self.metadata_path.name)}.{etag}.incomplete"
+        resolved_path = str(path.resolve())
+        # Some Windows versions do not allow for paths longer than 255 characters.
+        # In this case, we must specify it as an extended path by using the "\\?\" prefix.
+        if len(resolved_path) > 255 and not resolved_path.startswith("\\\\?\\"):
+            path = Path("\\\\?\\" + resolved_path)
+        return path
 
 
 @dataclass(frozen=True)

src/huggingface_hub/file_download.py

@@ -1136,10 +1136,18 @@ def _hf_hub_download_to_cache_dir(
 
     # Some Windows versions do not allow for paths longer than 255 characters.
     # In this case, we must specify it as an extended path by using the "\\?\" prefix.
-    if os.name == "nt" and len(os.path.abspath(lock_path)) > 255:
+    if (
+        os.name == "nt"
+        and len(os.path.abspath(lock_path)) > 255
+        and not os.path.abspath(lock_path).startswith("\\\\?\\")
+    ):
         lock_path = "\\\\?\\" + os.path.abspath(lock_path)
 
-    if os.name == "nt" and len(os.path.abspath(blob_path)) > 255:
+    if (
+        os.name == "nt"
+        and len(os.path.abspath(blob_path)) > 255
+        and not os.path.abspath(blob_path).startswith("\\\\?\\")
+    ):
         blob_path = "\\\\?\\" + os.path.abspath(blob_path)
 
     Path(lock_path).parent.mkdir(parents=True, exist_ok=True)