Log a warning for uncommitted changes on transaction exit

src/lakefs_spec/transaction.py

@@ -7,6 +7,7 @@
 import logging
 import random
 import string
+import warnings
 from collections import deque
 from typing import TYPE_CHECKING, Literal, TypeVar
 
@@ -132,6 +133,12 @@ def __exit__(self, exc_type, exc_val, exc_tb):
         self.fs._intrans = False
         self.fs._transaction = None
 
+        if any(self._ephemeral_branch.uncommitted()):
+            msg = f"Finished transaction on branch {self._ephemeral_branch.id!r} with uncommitted changes."
+            if self.delete != "never":
+                msg += " Objects added but not committed are lost."
+            warnings.warn(msg)
+
         if success and self.automerge:
             if any(self.base_branch.diff(self._ephemeral_branch)):
                 self._ephemeral_branch.merge_into(self.base_branch)

tests/test_transactions.py

@@ -146,3 +146,33 @@ def test_transaction_bad_repo(fs: LakeFSFileSystem) -> None:
     with pytest.raises(ValueError, match="repository .* does not exist"):
         with fs.transaction(repository="REEEE"):
             pass
+
+
+def test_warn_uncommitted_changes(
+    random_file_factory: RandomFileFactory,
+    fs: LakeFSFileSystem,
+    repository: Repository,
+    temp_branch: Branch,
+) -> None:
+    random_file = random_file_factory.make()
+
+    lpath = str(random_file)
+
+    with pytest.warns(match="uncommitted changes.*lost"):
+        with fs.transaction(repository, temp_branch) as tx:
+            fs.put_file(lpath, f"{repository.id}/{tx.branch.id}/{random_file.name}")
+
+
+def test_warn_uncommitted_changes_on_persisted_branch(
+    random_file_factory: RandomFileFactory,
+    fs: LakeFSFileSystem,
+    repository: Repository,
+    temp_branch: Branch,
+) -> None:
+    random_file = random_file_factory.make()
+
+    lpath = str(random_file)
+
+    with pytest.warns(match="uncommitted changes(?:(?!lost).)*$"):
+        with fs.transaction(repository, temp_branch, delete="never") as tx:
+            fs.put_file(lpath, f"{repository.id}/{tx.branch.id}/{random_file.name}")