Check symlinks support per directory instead of globally

src/huggingface_hub/file_download.py

@@ -172,33 +172,51 @@ def get_jinja_version():
     return _jinja_version
 
 
-_are_symlinks_supported: Optional[bool] = None
+_are_symlinks_supported_in_dir: Dict[str, bool] = {}
 
 
-def are_symlinks_supported() -> bool:
-    # Check symlink compatibility only once at first time use
-    global _are_symlinks_supported
+def are_symlinks_supported(cache_dir: Union[str, Path, None] = None) -> bool:
+    """Return whether the symlinks are supported on the machine.
 
-    if _are_symlinks_supported is None:
-        _are_symlinks_supported = True
+    Since symlinks support can change depending on the mounted disk, we need to check
+    on the precise cache folder. By default, the default HF cache directory is checked.
 
-        with tempfile.TemporaryDirectory() as tmpdir:
+    Args:
+        cache_dir (`str`, `Path`, *optional*):
+            Path to the folder where cached files are stored.
+
+    Returns: [bool] Whether symlinks are supported in the directory.
+    """
+    # Defaults to HF cache
+    if cache_dir is None:
+        cache_dir = HUGGINGFACE_HUB_CACHE
+    cache_dir = str(Path(cache_dir).expanduser().resolve())  # make it unique
+
+    # Check symlink compatibility only once (per cache directory) at first time use
+    if cache_dir not in _are_symlinks_supported_in_dir:
+        _are_symlinks_supported_in_dir[cache_dir] = True
+
+        os.makedirs(cache_dir, exist_ok=True)
+        with tempfile.TemporaryDirectory(dir=cache_dir) as tmpdir:
             src_path = Path(tmpdir) / "dummy_file_src"
             src_path.touch()
             dst_path = Path(tmpdir) / "dummy_file_dst"
+
+            # Relative source path as in `_create_relative_symlink``
+            relative_src = os.path.relpath(src_path, start=os.path.dirname(dst_path))
             try:
-                os.symlink(src_path, dst_path)
+                os.symlink(relative_src, dst_path)
             except OSError:
                 # Likely running on Windows
-                _are_symlinks_supported = False
+                _are_symlinks_supported_in_dir[cache_dir] = False
 
                 if not os.environ.get("DISABLE_SYMLINKS_WARNING"):
                     message = (
                         "`huggingface_hub` cache-system uses symlinks by default to"
-                        " efficiently store duplicated files but your machine doesn't"
-                        " support them. Caching files will still work but in a degraded"
-                        " version that might require more space on your disk. This"
-                        " warning can be disabled by setting the"
+                        " efficiently store duplicated files but your machine does not"
+                        f" support them in {cache_dir}. Caching files will still work"
+                        " but in a degraded version that might require more space on"
+                        " your disk. This warning can be disabled by setting the"
                         " `DISABLE_SYMLINKS_WARNING` environment variable. For more"
                         " details, see"
                         " https://huggingface.co/docs/huggingface_hub/how-to-cache#limitations."
@@ -213,7 +231,7 @@ def are_symlinks_supported() -> bool:
                         )
                     warnings.warn(message)
 
-    return _are_symlinks_supported
+    return _are_symlinks_supported_in_dir[cache_dir]
 
 
 # Return value when trying to load a file from cache but the file does not exist in the distant repo.
@@ -920,7 +938,8 @@ def _create_relative_symlink(src: str, dst: str, new_blob: bool = False) -> None
     except OSError:
         pass
 
-    if are_symlinks_supported():
+    cache_dir = os.path.dirname(os.path.commonpath([src, dst]))
+    if are_symlinks_supported(cache_dir=cache_dir):
         os.symlink(relative_src, dst)
     elif new_blob:
         os.replace(src, dst)

tests/test_cache_no_symlinks.py

@@ -6,7 +6,7 @@
 import pytest
 
 from huggingface_hub import hf_hub_download, scan_cache_dir
-from huggingface_hub.constants import CONFIG_NAME
+from huggingface_hub.constants import CONFIG_NAME, HUGGINGFACE_HUB_CACHE
 from huggingface_hub.file_download import are_symlinks_supported
 
 from .testing_constants import TOKEN
@@ -18,24 +18,35 @@
 class TestCacheLayoutIfSymlinksNotSupported(unittest.TestCase):
     cache_dir: Path
 
-    @patch("huggingface_hub.file_download._are_symlinks_supported", None)
-    def test_are_symlinks_supported_normal(self) -> None:
+    @patch(
+        "huggingface_hub.file_download._are_symlinks_supported_in_dir",
+        {HUGGINGFACE_HUB_CACHE: True},
+    )
+    def test_are_symlinks_supported_default(self) -> None:
         self.assertTrue(are_symlinks_supported())
 
-    @patch("huggingface_hub.file_download.os.symlink")  # Symlinks not supported
-    @patch("huggingface_hub.file_download._are_symlinks_supported", None)  # first use
-    def test_are_symlinks_supported_windows(self, mock_symlink: Mock) -> None:
-        mock_symlink.side_effect = OSError()
+    @patch("huggingface_hub.file_download.os.symlink")
+    @patch("huggingface_hub.file_download._are_symlinks_supported_in_dir", {})
+    def test_are_symlinks_supported_windows_specific_dir(
+        self, mock_symlink: Mock
+    ) -> None:
+        mock_symlink.side_effect = [OSError(), None]  # First dir not supported then yes
+        this_dir = Path(__file__).parent
 
-        # First time: warning is raised
+        # First time in `this_dir`: warning is raised
         with self.assertWarns(UserWarning):
-            self.assertFalse(are_symlinks_supported())
+            self.assertFalse(are_symlinks_supported(this_dir))
 
-        # Afterward: value is cached (no warning raised)
         with warnings.catch_warnings():
+            # Assert no warnings raised
             # Taken from https://stackoverflow.com/a/45671804
             warnings.simplefilter("error")
-            self.assertFalse(are_symlinks_supported())
+
+            # Second time in `this_dir` but with absolute path: value is still cached
+            self.assertFalse(are_symlinks_supported(this_dir.absolute()))
+
+            # Try with another directory: symlinks are supported, no warnings
+            self.assertTrue(are_symlinks_supported())  # True
 
     @patch("huggingface_hub.file_download.are_symlinks_supported")
     def test_download_no_symlink_new_file(