[PATCH 0/8] odb: write alternates at creation time

Hi,

writing alternates into the object database currently happens via `odb_source_write_alternate()`. But while that creates the ability to create alternates at arbitrary points of a source's lifetime, we don't use that functionality in the first place. Instead, we only ever write alternates when creating a new repository.

This design is suboptimal due to a couple of reasons:

  - It requires us to have a `write_alternates()` callback, which is
    overblown as we never even write alternates to an object database
    after it has been created.

  - We're about to make alternates an implementation detail of the
    object database's backend in a future patch series, so alternate
    implementations may not even support them.

  - The backend has more flexibility with how exactly alternates are
    configured when it itself is in full control over their setup at the
    time where it creates the object database itself.

This patch series thus refactors how we handle alternates so that we don't write them ad-hoc anymore. Instead, the series introduces a new option for `odb_source_create_on_disk()` that makes it handle those alternates at creation time.

This is part of the bigger goal of moving handling of alternates into the "files" backend.

This series is built on top of 2c3adbb2c4 (The 18th batch, 2026-08-24) with ps/odb-eagerly-load-alternates at 0076dc9f81 (odb: drop `alternates_db` field, 2026-08-17) merged into it.

Thanks!

Patrick

---
Patrick Steinhardt (8):
      builtin/clone: defer setup of the object database
      builtin/clone: move around `setup_reference()`
      builtin/clone: refactor handling of "--reference{,-if-able}"
      builtin/clone: move setup of alternates for shared local clones
      builtin/clone: move setup of alternates for non-shared local clones
      odb/source: support writing alternates when creating the database
      builtin/clone: write alternates via `odb_create_on_disk()`
      odb/source: remove the ability to write alternates

 builtin/clone.c            | 108 ++++++++++++++++++++++++--------------
 odb.c                      |   9 ----
 odb.h                      |   7 ---
 odb/source-files.c         | 128 +++++++++++++++++++++++++--------------------
 odb/source-inmemory.c      |   7 ---
 odb/source-loose.c         |   7 ---
 odb/source-packed.c        |   7 ---
 odb/source.h               |  44 ++++++----------
 setup.c                    |  15 ++++--
 setup.h                    |  15 ++++--
 t/t5604-clone-reference.sh |  25 +++++++++
 11 files changed, 201 insertions(+), 171 deletions(-)

--- base-commit: afa255aeb620346d56a2c01fb5ae9163513c56d7 change-id: 20260813-pks-odb-write-alternates-at-creation-time-64010deb94a0