[PATCH v2 0/2] rebase: support --trailer

From: Li Chen <redacted>

This two-patch series teaches git rebase a new
--trailer <text> option and, as a prerequisite, moves all trailer
handling out of the external interpret-trailers helper and into the
builtin code path, as suggested by Phillip Wood.

Patch 1 switches trailer.c to an in-memory implementation
(amend_strbuf_with_trailers()). It removes every fork/exec.

Patch 2 builds on that helper to implement
git rebase --trailer. When the option is given we:
force the merge backend (apply/am backend lacks a message filter),
automatically enable --force-rebase so that fast-forwarded
commits are rewritten, and append the requested trailer(s) to every
rewritten commit.
State is stored in $state_dir/trailer so an interrupted rebase can
resume safely. A dedicated test-suite (t3440) exercises plain,
conflict, --root, invalid-input scenarios and etc.

All t/*.sh testcases have run successfully.
Github CI tests have all been past: https://github.com/FirstLoveLife/git/actions/runs/15558597606/job/43805117563
(except for debian built test because of network issue)

RFC link: https://lore.kernel.org/git/196a5ac1393.f5b4db7d187309.2451613571977217927@linux.beauty/ (local)

The review comments from Phillip in the RFC series have been fixed. 
Thanks a lot for Phillip's great review!

Comments welcome!

Li Chen (2):
  trailer: append trailers in-process and drop the fork to
    `interpret-trailers`
  rebase: support --trailer

 Documentation/git-rebase.adoc |   7 ++
 builtin/rebase.c              |  98 +++++++++++++++++++++++
 sequencer.c                   |  13 +++
 sequencer.h                   |   3 +
 t/meson.build                 |   1 +
 t/t3440-rebase-trailer.sh     |  95 ++++++++++++++++++++++
 trailer.c                     | 147 +++++++++++++++++++++++++++++++---
 trailer.h                     |  17 ++++
 8 files changed, 372 insertions(+), 9 deletions(-)
 create mode 100755 t/t3440-rebase-trailer.sh

-- 
2.49.0