[PATCH v5 00/29] rebase: support --trailer

From: Li Chen <chenl311@chinatelecom.cn>

This 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 0 switches trailer.c to an in-memory implementation (amend_strbuf_with_trailers()). It removes every fork/exec.

Patch 1~8 fix all reviewer comments from v3 for patch 0. 

Patch 9 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.

The rest patches address all reviewer comments from v3 for patch 9. 

All t/*.sh testcases have run successfully.

v5: fix all Kristoffer's review comments form v4[3] in place and without new patches. 
v4: fix all reviewer comments in v3. [2], and add patch 1~8 & 10~29 to fix review comments.
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/ [2]: https://lore.kernel.org/git/20250803150059.402017-1-me@linux.beauty/ [3]: https://lore.kernel.org/git/20251014122452.1851103-1-me@linux.beauty/

Li Chen (29):
  trailer: append trailers in-process and drop the fork to
    `interpret-trailers`
  trailer: restore interpret_trailers helper
  trailer: drop --trailer prefix handling in amend helper
  trailer: move config_head and arg_head to if storage
  trailer: use bool for had_trailer_before
  interpret-trailers: buffer stdout output
  trailer: mirror interpret-trailers output flow
  trailer: handle trailer append failures gently
  rebase: support --trailer
  rebase: inline trailer state paths
  rebase: reuse buffer for trailer args
  rebase: drop redundant strbuf_release call
  rebase: skip stripping of --trailer option prefix
  rebase: die on invalid trailer args
  rebase: validate trailers with configured separators
  sequencer: add trailers to message before writing file
  t3440: create expect files at point of use
  t3440: check apply backend error includes option
  t3440: use test_commit_message for trailer checks
  t3440: drop redundant resets and pass branch to rebase where needed
  t3440: assert trailer on HEAD after conflict rebase
  rebase: persist --trailer options across restarts
  t3440: remove redundant --keep-empty
  t3440: use helper for trailer checks
  t3440: test --trailer without values
  t3440: convert ex.com to example.com
  t3440: ensure trailers persist after rebase continue
  t3440: exercise trailer config mapping
  sequencer: honor --trailer with fixup -C

 Documentation/git-rebase.adoc |   9 ++-
 builtin/commit.c              |   2 +-
 builtin/interpret-trailers.c  |  94 +++++-------------------
 builtin/rebase.c              |  50 +++++++++++++
 builtin/tag.c                 |   3 +-
 sequencer.c                   |  34 +++++++++
 sequencer.h                   |   4 +-
 t/meson.build                 |   1 +
 t/t3440-rebase-trailer.sh     | 134 ++++++++++++++++++++++++++++++++++
 trailer.c                     | 130 ++++++++++++++++++++++++++++++---
 trailer.h                     |  23 +++++-
 wrapper.c                     |  16 ++++
 wrapper.h                     |   6 ++
 13 files changed, 412 insertions(+), 94 deletions(-)
 create mode 100755 t/t3440-rebase-trailer.sh