Don't write the ref file unless necessary

src/huggingface_hub/_snapshot_download.py

@@ -254,11 +254,26 @@ def snapshot_download(
     # if passed revision is not identical to commit_hash
     # then revision has to be a branch name or tag name.
     # In that case store a ref.
-    if revision != commit_hash:
-        ref_path = os.path.join(storage_folder, "refs", revision)
-        os.makedirs(os.path.dirname(ref_path), exist_ok=True)
-        with open(ref_path, "w") as f:
-            f.write(commit_hash)
+    ref_path = os.path.join(storage_folder, "refs", revision)
+    # If the file exists, read the commit hash from it
+    write_commit_hash = True
+    if os.path.exists(ref_path):
+        try:
+            with open(ref_path) as f:
+                existing_commit_hash = f.read()
+            if existing_commit_hash == commit_hash:
+                write_commit_hash = False
+        except Exception as e:
+            logger.warning(f"Error reading commit hash from {ref_path}: {e}")
+
+    try:
+        # Write the commit hash to the ref file if it doesn't exist or is different
+        if revision != commit_hash and write_commit_hash:
+            os.makedirs(os.path.dirname(ref_path), exist_ok=True)
+            with open(ref_path, "w") as f:
+                f.write(commit_hash)
+    except Exception as e:
+        logger.warning(f"Error writing commit hash to {ref_path}: {e}")
 
     # we pass the commit_hash to hf_hub_download
     # so no network call happens if we already