feat(gix): read object headers with native lookup

Use GixPython's header lookup for `Git.get_object_header` and ODB metadata. Preserve the existing object-ID, kind and size tuple, missing-object behavior, and CLI diagnostics for unsupported storage or revision syntax. Keep the persistent-process lifecycle regressions explicitly exercising the CLI fallback.

The staged version passes Ruff and Python syntax checks. Its SHA-1/SHA-256 native smoke and focused pytest selection pass: 10 passed in 4.34s.

Author: codex

git/_backend.py

@@ -9,6 +9,7 @@
 from importlib import import_module
 import logging
 import os
+import re
 from threading import Lock
 from typing import Any, Callable, Dict, List, Sequence, Tuple
 
@@ -84,6 +85,39 @@ def _repository(command: Any, env: Dict[str, Any], *, query_config: bool = False
     return repo
 
 
+def _oid(repo: Any, ref: Any) -> Any:
+    ref = safe_decode(ref) if isinstance(ref, bytes) else str(ref)
+    if re.fullmatch(r"[a-fA-F0-9]{40}|[a-fA-F0-9]{64}", ref):
+        return gix.ObjectId(ref)
+    if ref.startswith(":/") or "^{/" in ref or "-dirty" in ref or re.search(r"-\d+-g[0-9a-fA-F]+", ref):
+        raise _Unsupported("revision grammar differences (GIX-17)")
+    if not hasattr(repo, "rev_parse_single"):
+        raise _Unsupported("revision feature disabled")
+    return repo.rev_parse_single(ref)
+
+
+def object_data(command: Any, ref: bytes) -> Any:
+    """Use native object reads without changing the public cat-file interface."""
+    if gix is None:
+        return NotImplemented
+    method = "get_object_header"
+    command._require_version()
+    try:
+        repo = _repository(command, {})
+        oid = _oid(repo, ref)
+        header = repo.try_find_header(oid)
+        if header is None:
+            raise ValueError("SHA %s could not be resolved" % oid)
+        result: Tuple[Any, ...] = (str(oid), header.kind(), header.size())
+    except _Unsupported as exc:
+        return _fallback(method, str(exc))
+    except gix.Error as exc:
+        _logger.debug("%s native read: %s", method, exc)
+        return _fallback(method, "native read diagnostics")
+    record(method, "native")
+    return result
+
+
 _HANDLERS: Dict[str, Callable[[Any, List[str], Dict[str, Any]], bytes]] = {}
 
 

git/cmd.py

@@ -2062,6 +2062,9 @@ def get_object_header(self, ref: Union[str, bytes]) -> Tuple[str, str, int]:
             (hexsha, type_string, size_as_int)
         """
         request = self._prepare_ref(ref)
+        native = _backend.object_data(self, request[:-1])
+        if native is not NotImplemented:
+            return native
         cmd = self._get_persistent_cmd("cat_file_header", "cat_file", batch_check=True, Z=True)
         return self.__get_object_header(cmd, request)
 

test/test_submodule.py

@@ -618,6 +618,8 @@ def test_submodule_rejects_checkout_and_gitmodules_symlinks(movable_submodule, t
 
 def test_add_closes_checkout_processes(movable_submodule, monkeypatch):
     """Adding a submodule must not leave a child process holding its checkout open."""
+    # Native reads have no persistent process; keep exercising the CLI fallback.
+    monkeypatch.setattr(git._backend, "object_data", lambda *args, **kwargs: NotImplemented)
     sm = movable_submodule
     checkout = Path(sm.repo.working_tree_dir, "new")
     execute = Git.execute
@@ -648,6 +650,7 @@ def capture_process(self, command, *args, **kwargs):
 
 @pytest.mark.parametrize("operation", ["update", "error", "recursive", "keep-going"])
 def test_update_closes_checkout_processes_retained_by_logging(movable_submodule, monkeypatch, caplog, operation):
+    monkeypatch.setattr(git._backend, "object_data", lambda *args, **kwargs: NotImplemented)
     sm = movable_submodule
     recursive = operation in ("recursive", "keep-going")
     with sm.module() as module: