[PATCH 00/17] odb: make object database sources pluggable

Hi,

this patch series finally makes the object database source pluggable. This is done by moving backend-specific logics into callback functions that are part of `struct odb_source` and providing thin wrappers that call those functions.

To set expectations: this is only a start, there is still functionality missing that needs to be made pluggable. Most importantly:

  - Counting of objects.

  - Abbreviating object IDs and finding ambiguous objects.

  - Consistency checks.

  - Optimizing the object database.

  - Generating packfiles.

These will all happen in later patch series. That being said, with this patch series one already gets a lot of the basic functionality, and it's almost possible to do local workflows. Only "almost" though because we rely on abbreviating object IDs in a lot of places, but once that part is implemented in a subsequent patch series you can indeed work locally with an alternate backend.

Furthermore, what I didn't include as part of this patch series just yet is the introduction of the "objectStorage" extension. I mostly wanted to focus on the mostly-trivial parts without introducing any change in behaviour.

Thanks!

Patrick

---
Patrick Steinhardt (17):
      odb: split `struct odb_source` into separate header
      odb: introduce "files" source
      odb: embed base source in the "files" backend
      odb: move reparenting logic into respective subsystems
      odb/source: introduce source type for robustness
      odb/source: make `free()` function pluggable
      odb/source: make `reprepare()` function pluggable
      odb/source: make `close()` function pluggable
      odb/source: make `read_object_info()` function pluggable
      odb/source: make `read_object_stream()` function pluggable
      odb/source: make `for_each_object()` function pluggable
      odb/source: make `freshen_object()` function pluggable
      odb/source: make `write_object()` function pluggable
      odb/source: make `write_object_stream()` function pluggable
      odb/source: make `read_alternates()` function pluggable
      odb/source: make `write_alternate()` function pluggable
      odb/source: make `begin_transaction()` function pluggable

 Makefile               |   2 +
 builtin/cat-file.c     |   3 +-
 builtin/fast-import.c  |  12 +-
 builtin/grep.c         |   6 +-
 builtin/index-pack.c   |   8 +-
 builtin/pack-objects.c |  13 +-
 commit-graph.c         |   6 +-
 http.c                 |   3 +-
 loose.c                |  23 ++-
 meson.build            |   2 +
 midx.c                 |  26 +--
 object-file.c          |  40 +++--
 odb.c                  | 191 +++-----------------
 odb.h                  |  86 +--------
 odb/source-files.c     | 239 +++++++++++++++++++++++++
 odb/source-files.h     |  35 ++++
 odb/source.c           |  38 ++++
 odb/source.h           | 464 +++++++++++++++++++++++++++++++++++++++++++++++++
 odb/streaming.c        |   8 +-
 packfile.c             |  36 ++--
 packfile.h             |   7 +-
 tmp-objdir.c           |  42 ++---
 tmp-objdir.h           |  15 --
 23 files changed, 950 insertions(+), 355 deletions(-)

--- base-commit: 197ce3527e423304844fef02ea067a85c0c75e70 change-id: 20260120-b4-pks-odb-source-pluggable-5c724250b3c8