[PATCH v3 0/2] rebase: support --trailer

From: Li Chen <chenl311@chinatelecom.cn>

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/16704004515

v3: merges the remaining trailer paths into one in-process helper, dropping the
    duplicate code, as pointed by Junio and Phillip [1]
v2: fix issues pointed by Phillip 
RFC link: https://lore.kernel.org/git/196a5ac1393.f5b4db7d187309.2451613571977217927@linux.beauty/

Comments welcome!

[1]: https://lore.kernel.org/git/xmqq8qlzkukw.fsf@gitster.g/

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

 Documentation/git-rebase.adoc |   7 ++
 builtin/interpret-trailers.c  | 117 ++++++++-----------------------
 builtin/rebase.c              |  98 ++++++++++++++++++++++++++
 sequencer.c                   |  13 ++++
 sequencer.h                   |   3 +
 t/meson.build                 |   1 +
 t/t3440-rebase-trailer.sh     |  95 ++++++++++++++++++++++++++
 trailer.c                     | 125 +++++++++++++++++++++++++++++++---
 trailer.h                     |  18 ++++-
 9 files changed, 375 insertions(+), 102 deletions(-)
 create mode 100755 t/t3440-rebase-trailer.sh