expand relative paths to full paths for the cache builder

src/levanter/store/tree_store.py

@@ -3,6 +3,7 @@
 
 import asyncio
 import os
+import urllib.parse
 from typing import Generic, List, Sequence, TypeVar
 
 import jax
@@ -48,7 +49,7 @@ class TreeStore(Generic[T]):
     tree: PyTree[JaggedArrayStore]
 
     def __init__(self, tree, path: str, mode: str):
-        self.path = path
+        self.path = _normalize_cache_dir(path)
         self.mode = mode
         self.tree = tree
 
@@ -61,8 +62,9 @@ def open(exemplar: T, path: str, *, mode="a", cache_metadata: bool = False) -> "
         """
         Open a TreeStoreBuilder from a file.
         """
-        tree = _construct_builder_tree(exemplar, path, mode, cache_metadata)
-        return TreeStore(tree, path, mode)
+        resolved_path = _normalize_cache_dir(path)
+        tree = _construct_builder_tree(exemplar, resolved_path, mode, cache_metadata)
+        return TreeStore(tree, resolved_path, mode)
 
     def append(self, ex: T):
         return self.extend([ex])
@@ -179,6 +181,31 @@ async def async_len(self) -> int:
         return await jax.tree.leaves(self.tree)[0].num_rows_async()
 
 
+def _normalize_cache_dir(path: os.PathLike[str] | str) -> str:
+    """Resolve relative file paths to absolute paths while leaving URLs untouched."""
+
+    path_str = os.fspath(path)
+
+    if _is_probably_url(path_str):
+        return path_str
+
+    expanded = os.path.expanduser(path_str)
+    return os.path.abspath(expanded)
+
+
+def _is_probably_url(path: str) -> bool:
+    parsed = urllib.parse.urlparse(path)
+
+    if parsed.scheme in ("", "file"):
+        return False
+
+    # Handle Windows drive letters like "C:\\" which urllib parses as a scheme.
+    if len(parsed.scheme) == 1 and path[1:2] == ":":
+        return False
+
+    return True
+
+
 def _construct_builder_tree(exemplar, path, mode, cache_metadata):
     def open_builder(tree_path, item):
         item = np.asarray(item)

tests/test_tree_store.py

@@ -1,6 +1,7 @@
 # Copyright 2025 The Levanter Authors
 # SPDX-License-Identifier: Apache-2.0
 
+import os
 import tempfile
 from typing import Any, Dict, Iterator, List, Sequence
 
@@ -44,6 +45,21 @@ def open_shard_at_row(self, shard_name: str, row: int) -> Iterator[List[int]]:
         return ([shard_num * 10 + i] * 10 for i in range(row, 10))
 
 
+def test_tree_store_resolves_relative_cache_dir(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    exemplar = {"data": np.array([0], dtype=np.int64)}
+    relative_path = "cache_dir"
+
+    store = TreeStore.open(exemplar, relative_path, mode="w")
+
+    expected_path = os.path.abspath(relative_path)
+    assert store.path == expected_path
+    assert os.path.isabs(store.path)
+
+    reloaded = store.reload()
+    assert reloaded.path == expected_path
+
+
 def test_tree_builder_with_processor():
     with tempfile.TemporaryDirectory() as tempdir:
         exemplar = {"data": np.array([0], dtype=np.int64)}