Support SAV publication without hard links

Author: TonisOrmisson

src/openstatspec/spss/sav.py

@@ -9,6 +9,7 @@
 import hashlib
 import os
 import json
+import errno
 import math
 import ctypes
 from contextlib import ExitStack, contextmanager
@@ -352,15 +353,28 @@ def _publish_staged_destination(
         state.update({"had_previous": True, "backup_installed": True})
     else:
         backup.unlink(missing_ok=True)
-
     # The hard-link claim is atomic and fails if another process publishes the
-    # destination after the check above. Staging is on the same filesystem.
-    os.link(staged, destination)
+    # destination after the check above. Some portable filesystems do not
+    # implement hard links; the surrounding export lock serializes those
+    # fallback replacements with every other OpenStatSpec publisher.
+    try:
+        os.link(staged, destination)
+    except OSError as link_error:
+        if link_error.errno not in {
+            errno.EOPNOTSUPP, errno.ENOTSUP, errno.EPERM, errno.EXDEV,
+        }:
+            raise
+        if _path_entry_exists(destination):
+            raise FileExistsError(
+                "The export destination was published by another operation."
+            ) from link_error
+        os.replace(staged, destination)
+    else:
+        staged.unlink()
     published_identity = _destination_identity(destination)
     if published_identity is None:
         raise FileNotFoundError("The published export destination disappeared.")
     state["published_identity"] = published_identity
-    staged.unlink()
 
 
 @contextmanager

tests/test_sav_sqlite.py

@@ -1,4 +1,5 @@
 import hashlib
+import errno
 import json
 import sqlite3
 import threading
@@ -384,3 +385,30 @@ def publish_concurrently(source, target):
     assert sav_module._path_entry_exists(backup) is False
     assert state["published_identity"] is None
 
+
+def test_export_publication_falls_back_when_hard_links_are_unsupported(
+    tmp_path, monkeypatch,
+) -> None:
+    staged = tmp_path / "staged.sav"
+    destination = tmp_path / "destination.sav"
+    backup = tmp_path / "destination.previous"
+    staged.write_bytes(b"portable staged export")
+
+    def unsupported_hard_link(*_args, **_kwargs):
+        raise OSError(errno.EOPNOTSUPP, "hard links are unsupported")
+
+    monkeypatch.setattr(sav_module.os, "link", unsupported_hard_link)
+    state = {}
+    sav_module._publish_staged_destination(
+        staged=staged,
+        destination=destination,
+        backup=backup,
+        state=state,
+    )
+
+    assert destination.read_bytes() == b"portable staged export"
+    assert not staged.exists()
+    assert state["published_identity"] == sav_module._destination_identity(
+        destination,
+    )
+