[PATCH 0/7] clone: fix init of refdb with wrong object format

Hi,

when using git-clone(1), we initialize the complete repository before we know about the object format used by the remote repository. This means that we'll potentially create the refdb with the wrong object format in case the local default object format and remote object format are not the same.

This isn't much of a problem in the context of the files backend, which never records the object format anyway. But it is a problem for the reftable backend, which indeed records the object format in the on-disk data structures. The result is thus a reftable with wrong object format.

This patch series aims to solve this issue by initializing the refdb at a later point after we have learned about the remote object format. This requires some careful reordering of code. Unfortunately, the end result is not easily verifiable and thus I didn't add tests here. But it does fix cloning of SHA256 repositories with the in-progress state of the reftable backend.

While at it I noticed that this actually fixes a bug with bundle URIs when the object formats diverge in this way.

The series is layed out as follows:

  - Patch 1 + 2: split out a function to create the refdb and make it
    possible to skip its initialization in `init_db()`.

  - Patch 3: allows git-remote-curl(1) to work with repos that get
    initialized during its lifetime.

  - Patch 4 - 6: address various corner cases where we access the refdb
    before we learned about the object format.

  - Patch 7: move initialization of the refdb to happen after we have
    learned about the object format.

This patch series is actually the last incompatibility for the reftable backend that I have found. All tests except for the files-backend specific ones pass now with the current state I have at [1], which is currently at e6f2f592b7 (t: skip tests which are incompatible with reftable, 2023-11-24)

Thanks in advance for your reviews!

Patrick

Patrick Steinhardt (7):
  setup: extract function to create the refdb
  setup: allow skipping creation of the refdb
  remote-curl: rediscover repository when fetching refs
  builtin/clone: fix bundle URIs with mismatching object formats
  builtin/clone: set up sparse checkout later
  builtin/clone: skip reading HEAD when retrieving remote
  builtin/clone: create the refdb with the correct object format

 builtin/clone.c             |  65 ++++++++++++----------
 remote-curl.c               |   7 ++-
 remote.c                    |  26 +++++----
 remote.h                    |   1 +
 setup.c                     | 106 +++++++++++++++++++++---------------
 setup.h                     |   6 +-
 t/t5558-clone-bundle-uri.sh |  18 ++++++
 7 files changed, 140 insertions(+), 89 deletions(-)