[PATCH 0/6] update-ref: add symref support for --stdin

From: Karthik Nayak <karthik.188@gmail.com>

The 'update-ref' command is used to update refs using transactions. The
command allows users to also utilize a '--stdin' mode to provide a
batch of sub-commands which can be processed in a transaction.
      
Currently, the sub-commands involve {verify, delete, create, update}
and they allow users to work with regular refs in the repository. To
work with symrefs, users only have the option of using
'git-symbolic-ref', which doesn't provide transaction support to the
users eventhough it uses the same behind the hood. 

Recently, we modified the reference backend to add symref support, following which, 'git-symbolic-ref' also uses the transaction backend. But, it doesn't expose this to the user. To allow users to work with symrefs via transaction, this series adds support for new sub-commands {symrer-verify, symref-delete, symref-create, symref-update} to the '--stdin' mode of update-ref. These complement the existing sub-commands.

The patches 1, 5 fix small issues in the reference backends. The other patches 2, 3, 4 & 6, each add one of the new sub-commands.

The series is based off master, with 'kn/ref-transaction-symref' merged in.

Karthik Nayak (6):
  refs: create and use `ref_update_ref_must_exist()`
  update-ref: add support for 'symref-verify' command
  update-ref: add support for 'symref-delete' command
  update-ref: add support for 'symref-create' command
  reftable: pick either 'oid' or 'target' for new updates
  update-ref: add support for 'symref-update' command

 Documentation/git-update-ref.txt |  25 ++
 builtin/clone.c                  |   2 +-
 builtin/fetch.c                  |   2 +-
 builtin/receive-pack.c           |   3 +-
 builtin/update-ref.c             | 230 +++++++++++++++++-
 refs.c                           |  34 ++-
 refs.h                           |   6 +-
 refs/files-backend.c             |   3 +-
 refs/refs-internal.h             |   6 +
 refs/reftable-backend.c          |   7 +-
 t/t0600-reffiles-backend.sh      |  32 +++
 t/t1400-update-ref.sh            | 404 ++++++++++++++++++++++++++++++-
 t/t1416-ref-transaction-hooks.sh |  54 +++++
 13 files changed, 775 insertions(+), 33 deletions(-)