Address review feedback about custom object directories

Review feedback noted that GIT_OBJECT_DIRECTORY made discovery succeed without becoming the Repo ODB root, while a relative value could later be resolved from the Git wrapper's different working directory.

Resolve the environment value against the construction directory, use it as the ODB root, and preserve the absolute value for later Git commands. The regression moves the only object store outside the git directory and verifies access through both GitDB and git cat-file after the original environment and current directory are restored.

Validation: 6 focused tests and 12 subtests; Ruff check and format; mypy; compileall; git diff --check.

Author: codex

git/repo/base.py

@@ -268,6 +268,9 @@ def __init__(
         """
 
         git_dir_env = os.getenv("GIT_DIR")
+        object_dir_env = os.getenv("GIT_OBJECT_DIRECTORY")
+        if object_dir_env is not None:
+            object_dir_env = osp.abspath(object_dir_env)
         epath = path or git_dir_env
         if not epath:
             epath = os.getcwd()
@@ -386,9 +389,11 @@ def __init__(
             self.git.update_environment(GIT_DIR=os.fspath(self.git_dir), GIT_COMMON_DIR=os.fspath(self.common_dir))
         elif git_dir_env is not None:
             self.git.update_environment(GIT_DIR=os.fspath(self.git_dir))
+        if object_dir_env is not None:
+            self.git.update_environment(GIT_OBJECT_DIRECTORY=object_dir_env)
 
         # Special handling, in special times.
-        rootpath = osp.join(self.common_dir, "objects")
+        rootpath = object_dir_env if object_dir_env is not None else osp.join(self.common_dir, "objects")
         if issubclass(odbt, GitCmdObjectDB):
             self.odb = odbt(rootpath, self.git)
         else:

test/test_repo.py

@@ -231,6 +231,26 @@ def test_repo_discovery_uses_storage_environment(self):
 
                 assert osp.samefile(Repo(git_dir).common_dir, byte_common_dir)
 
+    def test_repo_discovery_preserves_object_directory(self):
+        with tempfile.TemporaryDirectory() as tdir:
+            git_dir = Path(tdir) / "git"
+            payload = b"custom object database"
+            payload_file = Path(tdir) / "payload"
+            payload_file.write_bytes(payload)
+
+            source_repo = Repo.init(git_dir, bare=True)
+            blob_hexsha = source_repo.git.hash_object("-w", payload_file)
+            source_repo.close()
+            object_dir = Path(tdir) / "objects"
+            (git_dir / "objects").rename(object_dir)
+
+            with cwd(tdir), mock.patch.dict(os.environ, {"GIT_DIR": "git", "GIT_OBJECT_DIRECTORY": "objects"}):
+                repo = Repo(odbt=GitDB)
+
+            assert osp.samefile(repo.odb.root_path(), object_dir)
+            assert repo.odb.stream(bytes.fromhex(blob_hexsha)).read() == payload
+            assert repo.git.cat_file("blob", blob_hexsha) == payload.decode()
+
     @with_rw_repo("0.3.2.1")
     def test_repo_creation_from_different_paths(self, rw_repo):
         r_from_gitdir = Repo(rw_repo.git_dir)