fix(util): wait for contended locks with relative filenames

`BlockingLockFile('resource')` incorrectly treats the empty `dirname` of
`resource.lock` as a missing directory when another holder owns the lock.
Use `os.curdir` for that case so the retry and timeout paths work normally.

Add seven tests covering relative and absolute `str`/`Path` inputs, holder
release, timeouts and real missing parents. The complete Linux/Python 3.12
suite passes: 1696 tests, 89 existing skips, one existing xfail, 64 subtests.
Pinned hooks, mypy, basedpyright, docs, builds and strict Twine also pass.

Prepared by OpenAI Codex, an AI agent operating through FanWu-ai's account.

Author: FanWu-ai

git/util.py

@@ -1310,7 +1310,7 @@ def _obtain_lock(self) -> None:
                 # synity check: if the directory leading to the lockfile is not
                 # readable anymore, raise an exception
                 curtime = time.time()
-                if not osp.isdir(osp.dirname(self._lock_file_path())):
+                if not osp.isdir(osp.dirname(self._lock_file_path()) or osp.curdir):
                     msg = "Directory containing the lockfile %r was not readable anymore after waiting %g seconds" % (
                         self._lock_file_path(),
                         curtime - starttime,

test/test_util.py

@@ -862,3 +862,40 @@ def test_mode_str_to_int_accepts_bytes():
     assert mode_str_to_int(b"100644") == 0o100644
     assert mode_str_to_int("644") == 0o644
     assert mode_str_to_int(b"120000") == 0o120000
+
+
+@pytest.mark.parametrize("path_type", [str, pathlib.Path])
+@pytest.mark.parametrize("relative", [True, False])
+def test_blocking_lock_waits_for_existing_holder(tmp_path, monkeypatch, path_type, relative):
+    monkeypatch.chdir(tmp_path)
+    path = path_type("resource" if relative else tmp_path / "resource")
+    owner = LockFile(path)
+    waiter = BlockingLockFile(path, check_interval_s=0.01, max_block_time_s=1)
+    owner._obtain_lock()
+    try:
+        with mock.patch("git.util.time.sleep", side_effect=lambda _: owner._release_lock()) as sleep:
+            waiter._obtain_lock()
+            sleep.assert_called_once_with(0.01)
+        assert waiter._has_lock()
+    finally:
+        owner._release_lock()
+        waiter._release_lock()
+
+
+@pytest.mark.parametrize("path_type", [str, pathlib.Path])
+def test_blocking_relative_lock_reports_timeout(tmp_path, monkeypatch, path_type):
+    monkeypatch.chdir(tmp_path)
+    owner = LockFile(path_type("resource"))
+    waiter = BlockingLockFile(path_type("resource"), max_block_time_s=0)
+    owner._obtain_lock()
+    try:
+        with pytest.raises(OSError, match="Waited .* seconds for lock"):
+            waiter._obtain_lock()
+    finally:
+        owner._release_lock()
+
+
+def test_blocking_lock_still_rejects_missing_directory(tmp_path):
+    waiter = BlockingLockFile(tmp_path / "missing" / "resource")
+    with pytest.raises(OSError, match="Directory containing the lockfile"):
+        waiter._obtain_lock()