[PATCH v4 00/29] rebase: support --trailer

[PATCH v4 00/29] rebase: support --trailer

[Li Chen]

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.

v4: fix all reviewer comments in v3. [2]
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/

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
  tests: t3440: create expect files at point of use
  tests: t3440: check apply backend error includes option
  tests: t3440: use test_commit_message for trailer checks
  tests: t3440: drop redundant resets and pass branch to rebase where
    needed
  tests: t3440: assert trailer on HEAD after conflict rebase
  rebase: persist --trailer options across restarts
  tests: t3440: remove redundant --keep-empty
  tests: t3440: use helper for trailer checks
  tests: t3440: test --trailer without values
  tests: t3440: convert ex.com to example.com
  tests: t3440: ensure trailers persist after rebase continue
  tests: t3440: exercise trailer config mapping
  sequencer: honor --trailer with fixup -C

 Documentation/git-rebase.adoc |   7 ++
 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, 411 insertions(+), 93 deletions(-)
 create mode 100755 t/t3440-rebase-trailer.sh

-- 
2.51.0

[PATCH v4 01/29] trailer: append trailers in-process and drop the fork to `interpret-trailers`

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Route all trailer insertion through trailer_process() and make
builtin/interpret-trailers just do file I/O before calling into it.
amend_file_with_trailers() now shares the same code path.

This removes the fork/exec and tempfile juggling, cutting overhead and
simplifying error handling. No functional change is intended. It also
centralizes logic to prepare for follow-up rebase --trailer patch.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/interpret-trailers.c | 116 ++++++++------------------------
 trailer.c                    | 125 ++++++++++++++++++++++++++++++++---
 trailer.h                    |  18 ++++-
 3 files changed, 157 insertions(+), 102 deletions(-)

diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c
index 41b0750e5a..be0fa83f79 100644
--- a/builtin/interpret-trailers.c
+++ b/builtin/interpret-trailers.c
@@ -10,7 +10,6 @@
 #include "gettext.h"
 #include "parse-options.h"
 #include "string-list.h"
-#include "tempfile.h"
 #include "trailer.h"
 #include "config.h"
 
@@ -93,37 +92,6 @@ static int parse_opt_parse(const struct option *opt, const char *arg,
 	return 0;
 }
 
-static struct tempfile *trailers_tempfile;
-
-static FILE *create_in_place_tempfile(const char *file)
-{
-	struct stat st;
-	struct strbuf filename_template = STRBUF_INIT;
-	const char *tail;
-	FILE *outfile;
-
-	if (stat(file, &st))
-		die_errno(_("could not stat %s"), file);
-	if (!S_ISREG(st.st_mode))
-		die(_("file %s is not a regular file"), file);
-	if (!(st.st_mode & S_IWUSR))
-		die(_("file %s is not writable by user"), file);
-
-	/* Create temporary file in the same directory as the original */
-	tail = strrchr(file, '/');
-	if (tail)
-		strbuf_add(&filename_template, file, tail - file + 1);
-	strbuf_addstr(&filename_template, "git-interpret-trailers-XXXXXX");
-
-	trailers_tempfile = xmks_tempfile_m(filename_template.buf, st.st_mode);
-	strbuf_release(&filename_template);
-	outfile = fdopen_tempfile(trailers_tempfile, "w");
-	if (!outfile)
-		die_errno(_("could not open temporary file"));
-
-	return outfile;
-}
-
 static void read_input_file(struct strbuf *sb, const char *file)
 {
 	if (file) {
@@ -136,61 +104,6 @@ static void read_input_file(struct strbuf *sb, const char *file)
 	strbuf_complete_line(sb);
 }
 
-static void interpret_trailers(const struct process_trailer_options *opts,
-			       struct list_head *new_trailer_head,
-			       const char *file)
-{
-	LIST_HEAD(head);
-	struct strbuf sb = STRBUF_INIT;
-	struct strbuf trailer_block_sb = STRBUF_INIT;
-	struct trailer_block *trailer_block;
-	FILE *outfile = stdout;
-
-	trailer_config_init();
-
-	read_input_file(&sb, file);
-
-	if (opts->in_place)
-		outfile = create_in_place_tempfile(file);
-
-	trailer_block = parse_trailers(opts, sb.buf, &head);
-
-	/* Print the lines before the trailer block */
-	if (!opts->only_trailers)
-		fwrite(sb.buf, 1, trailer_block_start(trailer_block), outfile);
-
-	if (!opts->only_trailers && !blank_line_before_trailer_block(trailer_block))
-		fprintf(outfile, "\n");
-
-
-	if (!opts->only_input) {
-		LIST_HEAD(config_head);
-		LIST_HEAD(arg_head);
-		parse_trailers_from_config(&config_head);
-		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
-		list_splice(&config_head, &arg_head);
-		process_trailers_lists(&head, &arg_head);
-	}
-
-	/* Print trailer block. */
-	format_trailers(opts, &head, &trailer_block_sb);
-	free_trailers(&head);
-	fwrite(trailer_block_sb.buf, 1, trailer_block_sb.len, outfile);
-	strbuf_release(&trailer_block_sb);
-
-	/* Print the lines after the trailer block as is. */
-	if (!opts->only_trailers)
-		fwrite(sb.buf + trailer_block_end(trailer_block), 1,
-		       sb.len - trailer_block_end(trailer_block), outfile);
-	trailer_block_release(trailer_block);
-
-	if (opts->in_place)
-		if (rename_tempfile(&trailers_tempfile, file))
-			die_errno(_("could not rename temporary file to %s"), file);
-
-	strbuf_release(&sb);
-}
-
 int cmd_interpret_trailers(int argc,
 			   const char **argv,
 			   const char *prefix,
@@ -232,14 +145,37 @@ int cmd_interpret_trailers(int argc,
 			git_interpret_trailers_usage,
 			options);
 
+	trailer_config_init();
+
 	if (argc) {
 		int i;
-		for (i = 0; i < argc; i++)
-			interpret_trailers(&opts, &trailers, argv[i]);
+		for (i = 0; i < argc; i++) {
+			struct strbuf in_buf = STRBUF_INIT;
+			struct strbuf out_buf = STRBUF_INIT;
+
+			read_input_file(&in_buf, argv[i]);
+			if (trailer_process(&opts, in_buf.buf, &trailers, &out_buf) < 0)
+				die(_("failed to process trailers for %s"), argv[i]);
+			if (opts.in_place)
+				write_file_buf(argv[i], out_buf.buf, out_buf.len);
+			else
+				fwrite(out_buf.buf, 1, out_buf.len, stdout);
+			strbuf_release(&in_buf);
+			strbuf_release(&out_buf);
+		}
 	} else {
+		struct strbuf in_buf = STRBUF_INIT;
+		struct strbuf out_buf = STRBUF_INIT;
+
 		if (opts.in_place)
 			die(_("no input file given for in-place editing"));
-		interpret_trailers(&opts, &trailers, NULL);
+
+		read_input_file(&in_buf, NULL);
+		if (trailer_process(&opts, in_buf.buf, &trailers, &out_buf) < 0)
+			die(_("failed to process trailers"));
+		fwrite(out_buf.buf, 1, out_buf.len, stdout);
+		strbuf_release(&in_buf);
+		strbuf_release(&out_buf);
 	}
 
 	new_trailers_clear(&trailers);
diff --git a/trailer.c b/trailer.c
index 911a81ed99..8aec466b5f 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1224,14 +1224,121 @@ void trailer_iterator_release(struct trailer_iterator *iter)
 	strbuf_release(&iter->key);
 }
 
-int amend_file_with_trailers(const char *path, const struct strvec *trailer_args)
+static int amend_strbuf_with_trailers(struct strbuf *buf,
+									  const struct strvec *trailer_args)
 {
-	struct child_process run_trailer = CHILD_PROCESS_INIT;
-
-	run_trailer.git_cmd = 1;
-	strvec_pushl(&run_trailer.args, "interpret-trailers",
-		     "--in-place", "--no-divider",
-		     path, NULL);
-	strvec_pushv(&run_trailer.args, trailer_args->v);
-	return run_command(&run_trailer);
+	struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
+	LIST_HEAD(new_trailer_head);
+	struct strbuf out = STRBUF_INIT;
+	size_t i;
+
+	opts.no_divider = 1;
+
+	for (i = 0; i < trailer_args->nr; i++) {
+		const char *arg = trailer_args->v[i];
+		const char *text;
+		struct new_trailer_item *item;
+
+		if (!skip_prefix(arg, "--trailer=", &text))
+			text = arg;
+		if (!*text)
+			continue;
+		item = xcalloc(1, sizeof(*item));
+		INIT_LIST_HEAD(&item->list);
+		item->text = text;
+		list_add_tail(&item->list, &new_trailer_head);
+	}
+	if (trailer_process(&opts, buf->buf, &new_trailer_head, &out) < 0)
+		return -1;
+	strbuf_swap(buf, &out);
+	strbuf_release(&out);
+	while (!list_empty(&new_trailer_head)) {
+		struct new_trailer_item *item =
+			list_first_entry(&new_trailer_head, struct new_trailer_item, list);
+		list_del(&item->list);
+		free(item);
+	}
+	return 0;
+}
+
+int trailer_process(const struct process_trailer_options *opts,
+					const char *msg,
+					struct list_head *new_trailer_head,
+					struct strbuf *out)
+{
+	struct trailer_block *blk;
+	LIST_HEAD(orig_head);
+	LIST_HEAD(config_head);
+	LIST_HEAD(arg_head);
+	struct strbuf trailers_sb = STRBUF_INIT;
+	int had_trailer_before;
+
+	blk = parse_trailers(opts, msg, &orig_head);
+	had_trailer_before = !list_empty(&orig_head);
+	if (!opts->only_input) {
+		parse_trailers_from_config(&config_head);
+		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
+		list_splice(&config_head, &arg_head);
+		process_trailers_lists(&orig_head, &arg_head);
+	}
+	format_trailers(opts, &orig_head, &trailers_sb);
+	if (!opts->only_trailers && !opts->only_input && !opts->unfold &&
+	    !opts->trim_empty && list_empty(&orig_head) &&
+	    (list_empty(new_trailer_head) || opts->only_input)) {
+		size_t split = trailer_block_start(blk); /* end-of-log-msg */
+		if (!blank_line_before_trailer_block(blk)) {
+			strbuf_add(out, msg, split);
+			strbuf_addch(out, '\n');
+			strbuf_addstr(out, msg + split);
+		} else
+			strbuf_addstr(out, msg);
+
+		strbuf_release(&trailers_sb);
+		trailer_block_release(blk);
+		return 0;
+	}
+	if (opts->only_trailers) {
+		strbuf_addbuf(out, &trailers_sb);
+	} else if (had_trailer_before) {
+		strbuf_add(out, msg, trailer_block_start(blk));
+		if (!blank_line_before_trailer_block(blk))
+			strbuf_addch(out, '\n');
+		strbuf_addbuf(out, &trailers_sb);
+		strbuf_add(out, msg + trailer_block_end(blk),
+			   strlen(msg) - trailer_block_end(blk));
+	} else {
+		size_t cpos = trailer_block_start(blk);
+		strbuf_add(out, msg, cpos);
+		if (cpos == 0) /* empty body → just one \n */
+			strbuf_addch(out, '\n');
+		else if (!blank_line_before_trailer_block(blk))
+			strbuf_addch(out, '\n'); /* body without trailing blank */
+
+		strbuf_addbuf(out, &trailers_sb);
+		strbuf_add(out, msg + cpos, strlen(msg) - cpos);
+	}
+	strbuf_release(&trailers_sb);
+	free_trailers(&orig_head);
+	trailer_block_release(blk);
+	return 0;
+}
+
+int amend_file_with_trailers(const char *path,
+							 const struct strvec *trailer_args)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	if (!trailer_args || !trailer_args->nr)
+		return 0;
+
+	if (strbuf_read_file(&buf, path, 0) < 0)
+		return error_errno("could not read '%s'", path);
+
+	if (amend_strbuf_with_trailers(&buf, trailer_args))
+		die("failed to append trailers");
+
+	/* `write_file_buf()` aborts on error internally */
+	write_file_buf(path, buf.buf, buf.len);
+	strbuf_release(&buf);
+	return 0;
 }
diff --git a/trailer.h b/trailer.h
index 4740549586..01f711fb13 100644
--- a/trailer.h
+++ b/trailer.h
@@ -196,10 +196,22 @@ int trailer_iterator_advance(struct trailer_iterator *iter);
 void trailer_iterator_release(struct trailer_iterator *iter);
 
 /*
- * Augment a file to add trailers to it by running git-interpret-trailers.
- * This calls run_command() and its return value is the same (i.e. 0 for
- * success, various non-zero for other errors). See run-command.h.
+ * Augment a file to add trailers to it (similar to 'git interpret-trailers').
+ * Returns 0 on success or a non-zero error code on failure.
  */
 int amend_file_with_trailers(const char *path, const struct strvec *trailer_args);
 
+/*
+ * Process trailer lines for a commit message in-memory.
+ * @opts: trailer processing options (e.g. from parse-options)
+ * @msg: the input message string
+ * @new_trailer_head: list of new trailers to add (struct new_trailer_item)
+ * @out: strbuf to store the resulting message (must be initialized)
+ *
+ * Returns 0 on success, <0 on error.
+ */
+int trailer_process(const struct process_trailer_options *opts,
+			const char *msg,
+			struct list_head *new_trailer_head,
+			struct strbuf *out);
 #endif /* TRAILER_H */
-- 
2.51.0

Re: [PATCH v4 01/29] trailer: append trailers in-process and drop the fork to `interpret-trailers`

[Kristoffer Haugsbakk]

On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
> From: Li Chen <chenl311@chinatelecom.cn>
>
> Route all trailer insertion through trailer_process() and make
> builtin/interpret-trailers just do file I/O before calling into it.
> amend_file_with_trailers() now shares the same code path.
>
> This removes the fork/exec and tempfile juggling, cutting overhead and
> simplifying error handling. No functional change is intended. It also

Why “is intended” instead of “No functional change.”?

> centralizes logic to prepare for follow-up rebase --trailer patch.
>
> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
> ---
>  builtin/interpret-trailers.c | 116 ++++++++------------------------
>  trailer.c                    | 125 ++++++++++++++++++++++++++++++++---
>  trailer.h                    |  18 ++++-
>  3 files changed, 157 insertions(+), 102 deletions(-)
>[...]
>  	new_trailers_clear(&trailers);
> diff --git a/trailer.c b/trailer.c
> index 911a81ed99..8aec466b5f 100644
> --- a/trailer.c
> +++ b/trailer.c
> @@ -1224,14 +1224,121 @@ void trailer_iterator_release(struct
> trailer_iterator *iter)
>  	strbuf_release(&iter->key);
>  }
>
> -int amend_file_with_trailers(const char *path, const struct strvec
> *trailer_args)
> +static int amend_strbuf_with_trailers(struct strbuf *buf,
> +									  const struct strvec *trailer_args)

This needs Clang formatting.

>  {
> -	struct child_process run_trailer = CHILD_PROCESS_INIT;
>[snip]

Re: [PATCH v4 01/29] trailer: append trailers in-process and drop the fork to `interpret-trailers`

[Li Chen]

Hi Kristoffer


 ---- On Wed, 15 Oct 2025 04:43:09 +0800  Kristoffer Haugsbakk <kristofferhaugsbakk@fastmail.com> wrote --- 
 > On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
 > > From: Li Chen <chenl311@chinatelecom.cn>
 > >
 > > Route all trailer insertion through trailer_process() and make
 > > builtin/interpret-trailers just do file I/O before calling into it.
 > > amend_file_with_trailers() now shares the same code path.
 > >
 > > This removes the fork/exec and tempfile juggling, cutting overhead and
 > > simplifying error handling. No functional change is intended. It also
 > 
 > Why “is intended” instead of “No functional change.”?
 > 
 > > centralizes logic to prepare for follow-up rebase --trailer patch.
 > >
 > > Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
 > > ---
 > >  builtin/interpret-trailers.c | 116 ++++++++------------------------
 > >  trailer.c                    | 125 ++++++++++++++++++++++++++++++++---
 > >  trailer.h                    |  18 ++++-
 > >  3 files changed, 157 insertions(+), 102 deletions(-)
 > >[...]
 > >      new_trailers_clear(&trailers);
 > > diff --git a/trailer.c b/trailer.c
 > > index 911a81ed99..8aec466b5f 100644
 > > --- a/trailer.c
 > > +++ b/trailer.c
 > > @@ -1224,14 +1224,121 @@ void trailer_iterator_release(struct
 > > trailer_iterator *iter)
 > >      strbuf_release(&iter->key);
 > >  }
 > >
 > > -int amend_file_with_trailers(const char *path, const struct strvec
 > > *trailer_args)
 > > +static int amend_strbuf_with_trailers(struct strbuf *buf,
 > > +                                      const struct strvec *trailer_args)
 > 
 > This needs Clang formatting.

I apologize for the 4-space indentation in my previous codes due to my
editor settings, which is not align with this project(treat tab as 8 space)
I will use clang-format in the next version.

Regards,

Li​

[PATCH v4 02/29] trailer: restore interpret_trailers helper

[Li Chen]

The change factors the duplicated
read/process/write logic into a single
interpret_trailers() helper(which was removed
in previous commit) while preserving the
original error handling and output paths for
both in-place edits and stdout output.

cmd_interpret_trailers() now reuses the helper
for each filename and for the stdin path,
keeping the option parsing and safety checks intact.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/interpret-trailers.c | 50 +++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c
index be0fa83f79..2c8b6fc3b9 100644
--- a/builtin/interpret-trailers.c
+++ b/builtin/interpret-trailers.c
@@ -104,6 +104,30 @@ static void read_input_file(struct strbuf *sb, const char *file)
 	strbuf_complete_line(sb);
 }
 
+static void interpret_trailers(const struct process_trailer_options *opts,
+			       struct list_head *new_trailer_head,
+			       const char *file)
+{
+	struct strbuf in_buf = STRBUF_INIT;
+	struct strbuf out_buf = STRBUF_INIT;
+
+	read_input_file(&in_buf, file);
+	if (trailer_process(opts, in_buf.buf, new_trailer_head, &out_buf) < 0) {
+		if (file)
+			die(_("failed to process trailers for %s"), file);
+		else
+			die(_("failed to process trailers"));
+	}
+
+	if (opts->in_place)
+		write_file_buf(file, out_buf.buf, out_buf.len);
+	else
+		fwrite(out_buf.buf, 1, out_buf.len, stdout);
+
+	strbuf_release(&in_buf);
+	strbuf_release(&out_buf);
+}
+
 int cmd_interpret_trailers(int argc,
 			   const char **argv,
 			   const char *prefix,
@@ -149,33 +173,13 @@ int cmd_interpret_trailers(int argc,
 
 	if (argc) {
 		int i;
-		for (i = 0; i < argc; i++) {
-			struct strbuf in_buf = STRBUF_INIT;
-			struct strbuf out_buf = STRBUF_INIT;
-
-			read_input_file(&in_buf, argv[i]);
-			if (trailer_process(&opts, in_buf.buf, &trailers, &out_buf) < 0)
-				die(_("failed to process trailers for %s"), argv[i]);
-			if (opts.in_place)
-				write_file_buf(argv[i], out_buf.buf, out_buf.len);
-			else
-				fwrite(out_buf.buf, 1, out_buf.len, stdout);
-			strbuf_release(&in_buf);
-			strbuf_release(&out_buf);
-		}
+		for (i = 0; i < argc; i++)
+			interpret_trailers(&opts, &trailers, argv[i]);
 	} else {
-		struct strbuf in_buf = STRBUF_INIT;
-		struct strbuf out_buf = STRBUF_INIT;
-
 		if (opts.in_place)
 			die(_("no input file given for in-place editing"));
 
-		read_input_file(&in_buf, NULL);
-		if (trailer_process(&opts, in_buf.buf, &trailers, &out_buf) < 0)
-			die(_("failed to process trailers"));
-		fwrite(out_buf.buf, 1, out_buf.len, stdout);
-		strbuf_release(&in_buf);
-		strbuf_release(&out_buf);
+		interpret_trailers(&opts, &trailers, NULL);
 	}
 
 	new_trailers_clear(&trailers);
-- 
2.51.0

[PATCH v4 03/29] trailer: drop --trailer prefix handling in amend helper

[Li Chen]

Make callers pass plain trailer text instead of recreating
the option prefix before invoking interpret-trailers.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/commit.c | 2 +-
 builtin/tag.c    | 3 +--
 trailer.c        | 5 +----
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index 0243f17d53..67070d6a54 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1719,7 +1719,7 @@ int cmd_commit(int argc,
 		OPT_STRING(0, "fixup", &fixup_message, N_("[(amend|reword):]commit"), N_("use autosquash formatted message to fixup or amend/reword specified commit")),
 		OPT_STRING(0, "squash", &squash_message, N_("commit"), N_("use autosquash formatted message to squash specified commit")),
 		OPT_BOOL(0, "reset-author", &renew_authorship, N_("the commit is authored by me now (used with -C/-c/--amend)")),
-		OPT_PASSTHRU_ARGV(0, "trailer", &trailer_args, N_("trailer"), N_("add custom trailer(s)"), PARSE_OPT_NONEG),
+		OPT_CALLBACK_F(0, "trailer", &trailer_args, N_("trailer"), N_("add custom trailer(s)"), PARSE_OPT_NONEG, parse_opt_strvec),
 		OPT_BOOL('s', "signoff", &signoff, N_("add a Signed-off-by trailer")),
 		OPT_FILENAME('t', "template", &template_file, N_("use specified template file")),
 		OPT_BOOL('e', "edit", &edit_flag, N_("force edit of commit")),
diff --git a/builtin/tag.c b/builtin/tag.c
index f0665af3ac..65c4a0b36b 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -499,8 +499,7 @@ int cmd_tag(int argc,
 		OPT_CALLBACK_F('m', "message", &msg, N_("message"),
 			       N_("tag message"), PARSE_OPT_NONEG, parse_msg_arg),
 		OPT_FILENAME('F', "file", &msgfile, N_("read message from file")),
-		OPT_PASSTHRU_ARGV(0, "trailer", &trailer_args, N_("trailer"),
-				  N_("add custom trailer(s)"), PARSE_OPT_NONEG),
+		OPT_CALLBACK_F(0, "trailer", &trailer_args, N_("trailer"), N_("add custom trailer(s)"), PARSE_OPT_NONEG, parse_opt_strvec),
 		OPT_BOOL('e', "edit", &edit_flag, N_("force edit of tag message")),
 		OPT_BOOL('s', "sign", &opt.sign, N_("annotated and GPG-signed tag")),
 		OPT_CLEANUP(&cleanup_arg),
diff --git a/trailer.c b/trailer.c
index 8aec466b5f..42ac6f58a2 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1235,12 +1235,9 @@ static int amend_strbuf_with_trailers(struct strbuf *buf,
 	opts.no_divider = 1;
 
 	for (i = 0; i < trailer_args->nr; i++) {
-		const char *arg = trailer_args->v[i];
-		const char *text;
+		const char *text = trailer_args->v[i];
 		struct new_trailer_item *item;
 
-		if (!skip_prefix(arg, "--trailer=", &text))
-			text = arg;
 		if (!*text)
 			continue;
 		item = xcalloc(1, sizeof(*item));
-- 
2.51.0

[PATCH v4 04/29] trailer: move config_head and arg_head to if storage

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Move LIST_HEAD(config_head) and LIST_HEAD(arg_head) into the
non-only_input branch so they are created only when needed.
No functional change.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 trailer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/trailer.c b/trailer.c
index 42ac6f58a2..3169e315c0 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1265,14 +1265,15 @@ int trailer_process(const struct process_trailer_options *opts,
 {
 	struct trailer_block *blk;
 	LIST_HEAD(orig_head);
-	LIST_HEAD(config_head);
-	LIST_HEAD(arg_head);
 	struct strbuf trailers_sb = STRBUF_INIT;
 	int had_trailer_before;
 
 	blk = parse_trailers(opts, msg, &orig_head);
 	had_trailer_before = !list_empty(&orig_head);
 	if (!opts->only_input) {
+		LIST_HEAD(config_head);
+		LIST_HEAD(arg_head);
+
 		parse_trailers_from_config(&config_head);
 		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
 		list_splice(&config_head, &arg_head);
-- 
2.51.0

[PATCH v4 05/29] trailer: use bool for had_trailer_before

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Switch had_trailer_before from int to bool
to match its logical use. No functional change.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 trailer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/trailer.c b/trailer.c
index 3169e315c0..ac756020a3 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1266,7 +1266,7 @@ int trailer_process(const struct process_trailer_options *opts,
 	struct trailer_block *blk;
 	LIST_HEAD(orig_head);
 	struct strbuf trailers_sb = STRBUF_INIT;
-	int had_trailer_before;
+	bool had_trailer_before;
 
 	blk = parse_trailers(opts, msg, &orig_head);
 	had_trailer_before = !list_empty(&orig_head);
-- 
2.51.0

[PATCH v4 06/29] interpret-trailers: buffer stdout output

[Li Chen]

Simplified the non-in-place path in interpret_trailers
by writing the existing output strbuf directly to
stdout without creating a redundant temporary buffer.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/interpret-trailers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c
index 2c8b6fc3b9..cdf39dbca8 100644
--- a/builtin/interpret-trailers.c
+++ b/builtin/interpret-trailers.c
@@ -122,7 +122,7 @@ static void interpret_trailers(const struct process_trailer_options *opts,
 	if (opts->in_place)
 		write_file_buf(file, out_buf.buf, out_buf.len);
 	else
-		fwrite(out_buf.buf, 1, out_buf.len, stdout);
+		strbuf_write(&out_buf, stdout);
 
 	strbuf_release(&in_buf);
 	strbuf_release(&out_buf);
-- 
2.51.0

[PATCH v4 07/29] trailer: mirror interpret-trailers output flow

[Li Chen]

Drop the early-return branch that mirrored the
special case. Let trailer_process() always
follow the same path as interpret-trailers.
Ensure trailer lists and buffers are freed
along the unified exit path.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 trailer.c | 38 +++++++-------------------------------
 1 file changed, 7 insertions(+), 31 deletions(-)

diff --git a/trailer.c b/trailer.c
index ac756020a3..5329589064 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1266,10 +1266,8 @@ int trailer_process(const struct process_trailer_options *opts,
 	struct trailer_block *blk;
 	LIST_HEAD(orig_head);
 	struct strbuf trailers_sb = STRBUF_INIT;
-	bool had_trailer_before;
 
 	blk = parse_trailers(opts, msg, &orig_head);
-	had_trailer_before = !list_empty(&orig_head);
 	if (!opts->only_input) {
 		LIST_HEAD(config_head);
 		LIST_HEAD(arg_head);
@@ -1280,40 +1278,18 @@ int trailer_process(const struct process_trailer_options *opts,
 		process_trailers_lists(&orig_head, &arg_head);
 	}
 	format_trailers(opts, &orig_head, &trailers_sb);
-	if (!opts->only_trailers && !opts->only_input && !opts->unfold &&
-	    !opts->trim_empty && list_empty(&orig_head) &&
-	    (list_empty(new_trailer_head) || opts->only_input)) {
-		size_t split = trailer_block_start(blk); /* end-of-log-msg */
-		if (!blank_line_before_trailer_block(blk)) {
-			strbuf_add(out, msg, split);
-			strbuf_addch(out, '\n');
-			strbuf_addstr(out, msg + split);
-		} else
-			strbuf_addstr(out, msg);
-
-		strbuf_release(&trailers_sb);
-		trailer_block_release(blk);
-		return 0;
-	}
 	if (opts->only_trailers) {
 		strbuf_addbuf(out, &trailers_sb);
-	} else if (had_trailer_before) {
-		strbuf_add(out, msg, trailer_block_start(blk));
-		if (!blank_line_before_trailer_block(blk))
-			strbuf_addch(out, '\n');
-		strbuf_addbuf(out, &trailers_sb);
-		strbuf_add(out, msg + trailer_block_end(blk),
-			   strlen(msg) - trailer_block_end(blk));
 	} else {
-		size_t cpos = trailer_block_start(blk);
-		strbuf_add(out, msg, cpos);
-		if (cpos == 0) /* empty body → just one \n */
-			strbuf_addch(out, '\n');
-		else if (!blank_line_before_trailer_block(blk))
-			strbuf_addch(out, '\n'); /* body without trailing blank */
+		size_t block_start = trailer_block_start(blk);
+		size_t block_end = trailer_block_end(blk);
+		bool need_blank_line = !blank_line_before_trailer_block(blk);
 
+		strbuf_add(out, msg, block_start);
+		if (need_blank_line)
+			strbuf_addch(out, '\n');
 		strbuf_addbuf(out, &trailers_sb);
-		strbuf_add(out, msg + cpos, strlen(msg) - cpos);
+		strbuf_add(out, msg + block_end, strlen(msg) - block_end);
 	}
 	strbuf_release(&trailers_sb);
 	free_trailers(&orig_head);
-- 
2.51.0

[PATCH v4 08/29] trailer: handle trailer append failures gently

[Li Chen]

Added write_file_buf_gently so callers can rewrite
files while surfacing errors instead of aborting.

Updated amend_file_with_trailers to release buffers
and propagate trailer and write failures back to the caller,
because amend_file_with_trailers shuold not die.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 trailer.c | 14 ++++++++++----
 wrapper.c | 16 ++++++++++++++++
 wrapper.h |  6 ++++++
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/trailer.c b/trailer.c
index 5329589064..b0ad7dc5c3 100644
--- a/trailer.c
+++ b/trailer.c
@@ -9,6 +9,7 @@
 #include "commit.h"
 #include "trailer.h"
 #include "list.h"
+#include "wrapper.h"
 /*
  * Copyright (c) 2013, 2014 Christian Couder <chriscool@tuxfamily.org>
  */
@@ -1308,11 +1309,16 @@ int amend_file_with_trailers(const char *path,
 	if (strbuf_read_file(&buf, path, 0) < 0)
 		return error_errno("could not read '%s'", path);
 
-	if (amend_strbuf_with_trailers(&buf, trailer_args))
-		die("failed to append trailers");
+	if (amend_strbuf_with_trailers(&buf, trailer_args)) {
+		strbuf_release(&buf);
+		return error("failed to append trailers");
+	}
+
+	if (write_file_buf_gently(path, buf.buf, buf.len)) {
+		strbuf_release(&buf);
+		return -1;
+	}
 
-	/* `write_file_buf()` aborts on error internally */
-	write_file_buf(path, buf.buf, buf.len);
 	strbuf_release(&buf);
 	return 0;
 }
diff --git a/wrapper.c b/wrapper.c
index 2f00d2ac87..2aeba8b049 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -688,6 +688,22 @@ void write_file_buf(const char *path, const char *buf, size_t len)
 		die_errno(_("could not close '%s'"), path);
 }
 
+int write_file_buf_gently(const char *path, const char *buf, size_t len)
+{
+	int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0666);
+
+	if (fd < 0)
+		return error_errno(_("could not open '%s'"), path);
+	if (write_in_full(fd, buf, len) < 0) {
+		int ret = error_errno(_("could not write to '%s'"), path);
+		close(fd);
+		return ret;
+	}
+	if (close(fd))
+		return error_errno(_("could not close '%s'"), path);
+	return 0;
+}
+
 void write_file(const char *path, const char *fmt, ...)
 {
 	va_list params;
diff --git a/wrapper.h b/wrapper.h
index 7df824e34a..5b7d7a78fb 100644
--- a/wrapper.h
+++ b/wrapper.h
@@ -56,6 +56,12 @@ static inline ssize_t write_str_in_full(int fd, const char *str)
  */
 void write_file_buf(const char *path, const char *buf, size_t len);
 
+/**
+ * Like write_file_buf(), but report errors instead of exiting. Returns 0 on
+ * success or a negative value on error after emitting a message.
+ */
+int write_file_buf_gently(const char *path, const char *buf, size_t len);
+
 /**
  * Like write_file_buf(), but format the contents into a buffer first.
  * Additionally, write_file() will append a newline if one is not already
-- 
2.51.0

[PATCH v4 09/29] rebase: support --trailer

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Implement a new `--trailer <text>` option for `git rebase`
(support merge backend only now), which appends arbitrary
trailer lines to each rebased commit message.

Reject it if the user passes an option that requires the
apply backend (git am) since it lacks message‑filter/trailer
hook. otherwise we can just use the merge backend.

Automatically set REBASE_FORCE when any trailer is supplied.

And reject invalid input before user edit the interactive file.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 Documentation/git-rebase.adoc |  7 +++
 builtin/rebase.c              | 89 +++++++++++++++++++++++++++++++++
 sequencer.c                   | 13 +++++
 sequencer.h                   |  4 +-
 t/meson.build                 |  1 +
 t/t3440-rebase-trailer.sh     | 94 +++++++++++++++++++++++++++++++++++
 6 files changed, 207 insertions(+), 1 deletion(-)
 create mode 100755 t/t3440-rebase-trailer.sh

diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
index 005caf6164..b2003b70d7 100644
--- a/Documentation/git-rebase.adoc
+++ b/Documentation/git-rebase.adoc
@@ -488,6 +488,13 @@ See also INCOMPATIBLE OPTIONS below.
 	that if `--interactive` is given then only commits marked to be
 	picked, edited or reworded will have the trailer added.
 +
+--trailer <trailer>::
+       Append the given trailer line(s) to every rebased commit
+       message, processed via linkgit:git-interpret-trailers[1].
+       When this option is present *rebase automatically implies*
+       `--force-rebase` so that fast‑forwarded commits are also
+       rewritten.
+
 See also INCOMPATIBLE OPTIONS below.
 
 -i::
diff --git a/builtin/rebase.c b/builtin/rebase.c
index c468828189..3b001c0757 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -36,6 +36,7 @@
 #include "reset.h"
 #include "trace2.h"
 #include "hook.h"
+#include "trailer.h"
 
 static char const * const builtin_rebase_usage[] = {
 	N_("git rebase [-i] [options] [--exec <cmd>] "
@@ -113,6 +114,7 @@ struct rebase_options {
 	enum action action;
 	char *reflog_action;
 	int signoff;
+	struct strvec trailer_args;
 	int allow_rerere_autoupdate;
 	int keep_empty;
 	int autosquash;
@@ -143,6 +145,7 @@ struct rebase_options {
 		.flags = REBASE_NO_QUIET, 		\
 		.git_am_opts = STRVEC_INIT,		\
 		.exec = STRING_LIST_INIT_NODUP,		\
+		.trailer_args = STRVEC_INIT,  \
 		.git_format_patch_opt = STRBUF_INIT,	\
 		.fork_point = -1,			\
 		.reapply_cherry_picks = -1,             \
@@ -166,6 +169,7 @@ static void rebase_options_release(struct rebase_options *opts)
 	free(opts->strategy);
 	string_list_clear(&opts->strategy_opts, 0);
 	strbuf_release(&opts->git_format_patch_opt);
+	strvec_clear(&opts->trailer_args);
 }
 
 static struct replay_opts get_replay_opts(const struct rebase_options *opts)
@@ -177,6 +181,10 @@ static struct replay_opts get_replay_opts(const struct rebase_options *opts)
 	sequencer_init_config(&replay);
 
 	replay.signoff = opts->signoff;
+
+	for (size_t i = 0; i < opts->trailer_args.nr; i++)
+		strvec_push(&replay.trailer_args, opts->trailer_args.v[i]);
+
 	replay.allow_ff = !(opts->flags & REBASE_FORCE);
 	if (opts->allow_rerere_autoupdate)
 		replay.allow_rerere_auto = opts->allow_rerere_autoupdate;
@@ -434,6 +442,8 @@ static int read_basic_state(struct rebase_options *opts)
 	struct strbuf head_name = STRBUF_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct object_id oid;
+	const char trailer_state_name[] = "trailer";
+	const char *path = state_dir_path(trailer_state_name, opts);
 
 	if (!read_oneliner(&head_name, state_dir_path("head-name", opts),
 			   READ_ONELINER_WARN_MISSING) ||
@@ -502,11 +512,31 @@ static int read_basic_state(struct rebase_options *opts)
 
 	strbuf_release(&buf);
 
+	if (strbuf_read_file(&buf, path, 0) >= 0) {
+		const char *p = buf.buf, *end = buf.buf + buf.len;
+
+		while (p < end) {
+			char *nl = memchr(p, '\n', end - p);
+			if (!nl)
+				die("nl shouldn't be NULL");
+			*nl = '\0';
+
+			if (*p)
+				strvec_push(&opts->trailer_args, p);
+
+			p = nl + 1;
+		}
+		strbuf_release(&buf);
+	}
+	strbuf_release(&buf);
+
 	return 0;
 }
 
 static int rebase_write_basic_state(struct rebase_options *opts)
 {
+	const char trailer_state_name[] = "trailer";
+
 	write_file(state_dir_path("head-name", opts), "%s",
 		   opts->head_name ? opts->head_name : "detached HEAD");
 	write_file(state_dir_path("onto", opts), "%s",
@@ -528,6 +558,21 @@ static int rebase_write_basic_state(struct rebase_options *opts)
 	if (opts->signoff)
 		write_file(state_dir_path("signoff", opts), "--signoff");
 
+	/*
+	 * save opts->trailer_args into state_dir/trailer
+	 */
+	if (opts->trailer_args.nr) {
+		struct strbuf buf = STRBUF_INIT;
+
+		for (size_t i = 0; i < opts->trailer_args.nr; i++) {
+				strbuf_addstr(&buf, opts->trailer_args.v[i]);
+				strbuf_addch(&buf, '\n');
+		}
+		write_file(state_dir_path(trailer_state_name, opts),
+				   "%s", buf.buf);
+		strbuf_release(&buf);
+	}
+
 	return 0;
 }
 
@@ -1084,6 +1129,35 @@ static int check_exec_cmd(const char *cmd)
 	return 0;
 }
 
+static int validate_trailer_args_after_config(const struct strvec *cli_args,
+				       struct strbuf *err)
+{
+	for (size_t i = 0; i < cli_args->nr; i++) {
+		const char *raw = cli_args->v[i];
+		const char *txt; // Key[:=]Val
+		const char *sep;
+
+		if (!skip_prefix(raw, "--trailer=", &txt))
+			txt = raw;
+
+		if (!*txt) {
+			strbuf_addstr(err, _("empty --trailer argument"));
+			return -1;
+		}
+
+		sep = strpbrk(txt, ":=");
+
+		/* there must be key bfore seperator */
+		if (sep && sep == txt) {
+			strbuf_addf(err,
+				    _("invalid trailer '%s': missing key before separator"),
+				    txt);
+			return -1;
+		}
+	}
+	return 0;
+}
+
 int cmd_rebase(int argc,
 	       const char **argv,
 	       const char *prefix,
@@ -1132,6 +1206,8 @@ int cmd_rebase(int argc,
 			.flags = PARSE_OPT_NOARG,
 			.defval = REBASE_DIFFSTAT,
 		},
+		OPT_STRVEC(0, "trailer", &options.trailer_args, N_("trailer"),
+				N_("add custom trailer(s)")),
 		OPT_BOOL(0, "signoff", &options.signoff,
 			 N_("add a Signed-off-by trailer to each commit")),
 		OPT_BOOL(0, "committer-date-is-author-date",
@@ -1285,6 +1361,16 @@ int cmd_rebase(int argc,
 			     builtin_rebase_options,
 			     builtin_rebase_usage, 0);
 
+	if (options.trailer_args.nr) {
+		struct strbuf err = STRBUF_INIT;
+
+		if (validate_trailer_args_after_config(&options.trailer_args, &err))
+			die("%s", err.buf);
+
+		options.flags |= REBASE_FORCE;
+		strbuf_release(&err);
+	}
+
 	if (preserve_merges_selected)
 		die(_("--preserve-merges was replaced by --rebase-merges\n"
 			"Note: Your `pull.rebase` configuration may also be set to 'preserve',\n"
@@ -1542,6 +1628,9 @@ int cmd_rebase(int argc,
 	if (options.root && !options.onto_name)
 		imply_merge(&options, "--root without --onto");
 
+	if (options.trailer_args.nr)
+		imply_merge(&options, "--trailer");
+
 	if (isatty(2) && options.flags & REBASE_NO_QUIET)
 		strbuf_addstr(&options.git_format_patch_opt, " --progress");
 
diff --git a/sequencer.c b/sequencer.c
index 5476d39ba9..5103ae786c 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -420,6 +420,7 @@ void replay_opts_release(struct replay_opts *opts)
 	if (opts->revs)
 		release_revisions(opts->revs);
 	free(opts->revs);
+	strvec_clear(&opts->trailer_args);
 	replay_ctx_release(ctx);
 	free(opts->ctx);
 }
@@ -2517,6 +2518,18 @@ static int do_pick_commit(struct repository *r,
 			_("dropping %s %s -- patch contents already upstream\n"),
 			oid_to_hex(&commit->object.oid), msg.subject);
 	} /* else allow == 0 and there's nothing special to do */
+
+	if (!res && opts->trailer_args.nr && !drop_commit) {
+		const char *trailer_file =
+			msg_file ? msg_file : git_path_merge_msg(r);
+
+		if (amend_file_with_trailers(trailer_file,
+						&opts->trailer_args)) {
+			res = error(_("unable to add trailers to commit message"));
+			goto leave;
+		}
+	}
+
 	if (!opts->no_commit && !drop_commit) {
 		if (author || command == TODO_REVERT || (flags & AMEND_MSG))
 			res = do_commit(r, msg_file, author, reflog_action,
diff --git a/sequencer.h b/sequencer.h
index 719684c8a9..e21835c5a0 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -44,6 +44,7 @@ struct replay_opts {
 	int record_origin;
 	int no_commit;
 	int signoff;
+	struct strvec trailer_args;
 	int allow_ff;
 	int allow_rerere_auto;
 	int allow_empty;
@@ -82,8 +83,9 @@ struct replay_opts {
 	struct replay_ctx *ctx;
 };
 #define REPLAY_OPTS_INIT {			\
-	.edit = -1,				\
 	.action = -1,				\
+	.edit = -1,				\
+	.trailer_args = STRVEC_INIT, \
 	.xopts = STRVEC_INIT,			\
 	.ctx = replay_ctx_new(),		\
 }
diff --git a/t/meson.build b/t/meson.build
index 11376b9e25..13b44c9a7b 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -383,6 +383,7 @@ integration_tests = [
   't3436-rebase-more-options.sh',
   't3437-rebase-fixup-options.sh',
   't3438-rebase-broken-files.sh',
+  't3440-rebase-trailer.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
new file mode 100755
index 0000000000..c08a9c4abf
--- /dev/null
+++ b/t/t3440-rebase-trailer.sh
@@ -0,0 +1,94 @@
+#!/bin/sh
+#
+
+test_description='git rebase --trailer integration tests
+We verify that --trailer works with the merge backend,
+and that it is rejected early when the apply backend is requested.'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh # test_commit_message, helpers
+
+create_expect() {
+	cat >"$1" <<-EOF
+		$2
+
+		Reviewed-by: Dev <dev@example.com>
+	EOF
+}
+
+test_expect_success 'setup repo with a small history' '
+	git commit --allow-empty -m "Initial empty commit" &&
+	test_commit first file a &&
+	test_commit second file &&
+	git checkout -b conflict-branch first &&
+	test_commit file-2 file-2 &&
+	test_commit conflict file &&
+	test_commit third file &&
+	ident="$GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>" &&
+	create_expect initial-signed  "Initial empty commit" &&
+	create_expect first-signed    "first"                 &&
+	create_expect second-signed   "second"                &&
+	create_expect file2-signed    "file-2"                &&
+	create_expect third-signed    "third"                 &&
+	create_expect conflict-signed "conflict"
+'
+
+test_expect_success 'apply backend is rejected with --trailer' '
+	head_before=$(git rev-parse HEAD) &&
+	test_expect_code 128 \
+	git rebase --apply --trailer "Reviewed-by: Dev <dev@example.com>" \
+				HEAD^ 2>err &&
+	test_grep "requires the merge backend" err &&
+	test_cmp_rev HEAD $head_before
+'
+
+test_expect_success 'reject empty --trailer argument' '
+	git reset --hard third &&
+	test_expect_code 128 git rebase -m --trailer "" HEAD^ 2>err &&
+	test_grep "empty --trailer" err
+'
+
+test_expect_success 'reject trailer with missing key before separator' '
+	git reset --hard third &&
+	test_expect_code 128 git rebase -m --trailer ": no-key" HEAD^ 2>err &&
+	test_grep "missing key before separator" err
+'
+
+test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last' '
+	git reset --hard third &&
+	git -c trailer.Bug.ifexists=replace -c trailer.Bug.ifmissing=add rebase -m --trailer "Bug: 123" --trailer "Bug: 456" HEAD~1 &&
+	git cat-file commit HEAD | grep "^Bug: 456" &&
+	git cat-file commit HEAD | grep -v "^Bug: 123"
+'
+
+test_expect_success 'multiple Signed-off-by trailers all preserved' '
+	git reset --hard third &&
+	git rebase -m \
+		--trailer "Signed-off-by: Dev A <a@ex.com>" \
+		--trailer "Signed-off-by: Dev B <b@ex.com>" HEAD~1 &&
+	git cat-file commit HEAD | grep -c "^Signed-off-by:" >count &&
+	test "$(cat count)" = 2   # two new commits
+'
+
+test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
+	git reset --hard third &&
+	test_must_fail git rebase -m \
+		--trailer "Reviewed-by: Dev <dev@example.com>" \
+		second third &&
+	git checkout --theirs file &&
+	git add file &&
+	git rebase --continue &&
+	test_commit_message HEAD~2 file2-signed
+'
+
+test_expect_success 'rebase --root --trailer updates every commit' '
+	git checkout first &&
+	git rebase --root --keep-empty \
+		--trailer "Reviewed-by: Dev <dev@example.com>" &&
+	test_commit_message HEAD   first-signed &&
+	test_commit_message HEAD^  initial-signed
+'
+test_done
-- 
2.51.0

Re: [PATCH v4 09/29] rebase: support --trailer

[Kristoffer Haugsbakk]

On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
> From: Li Chen <chenl311@chinatelecom.cn>
>
> Implement a new `--trailer <text>` option for `git rebase`
> (support merge backend only now), which appends arbitrary
> trailer lines to each rebased commit message.
>
> Reject it if the user passes an option that requires the
> apply backend (git am) since it lacks message‑filter/trailer
> hook. otherwise we can just use the merge backend.
>
> Automatically set REBASE_FORCE when any trailer is supplied.
>
> And reject invalid input before user edit the interactive file.

s/edit/edits/

>
> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
> ---
>  Documentation/git-rebase.adoc |  7 +++
>  builtin/rebase.c              | 89 +++++++++++++++++++++++++++++++++
>  sequencer.c                   | 13 +++++
>  sequencer.h                   |  4 +-
>  t/meson.build                 |  1 +
>  t/t3440-rebase-trailer.sh     | 94 +++++++++++++++++++++++++++++++++++
>  6 files changed, 207 insertions(+), 1 deletion(-)
>  create mode 100755 t/t3440-rebase-trailer.sh
>
> diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
> index 005caf6164..b2003b70d7 100644
> --- a/Documentation/git-rebase.adoc
> +++ b/Documentation/git-rebase.adoc
> @@ -488,6 +488,13 @@ See also INCOMPATIBLE OPTIONS below.
>  	that if `--interactive` is given then only commits marked to be
>  	picked, edited or reworded will have the trailer added.
>  +
> +--trailer <trailer>::
> +       Append the given trailer line(s) to every rebased commit
> +       message, processed via linkgit:git-interpret-trailers[1].
> +       When this option is present *rebase automatically implies*
> +       `--force-rebase` so that fast‑forwarded commits are also
> +       rewritten.
> +

You’ve cut off the second paragraph of `--signoff`.  This should be
added after `See also` below.

Probably also with an `=`:

    --trailer=<trailer>::

>  See also INCOMPATIBLE OPTIONS below.
>
>[snip]
> +GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
> +export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
> +
> +. ./test-lib.sh
> +. "$TEST_DIRECTORY"/lib-rebase.sh # test_commit_message, helpers
> +
> +create_expect() {
> +	cat >"$1" <<-EOF
> +		$2
> +
> +		Reviewed-by: Dev <dev@example.com>

One level of indentation seems enough?

> +	EOF
> +}
>[snip]

Long line.

> +	git cat-file commit HEAD | grep "^Bug: 456" &&
> +	git cat-file commit HEAD | grep -v "^Bug: 123"
> +'
>[snip]

Re: [PATCH v4 09/29] rebase: support --trailer

[Li Chen]

Hi Kristoffer


 ---- On Wed, 15 Oct 2025 04:43:33 +0800  Kristoffer Haugsbakk <kristofferhaugsbakk@fastmail.com> wrote --- 
 > On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
 > > From: Li Chen <chenl311@chinatelecom.cn>
 > >
 > > Implement a new `--trailer <text>` option for `git rebase`
 > > (support merge backend only now), which appends arbitrary
 > > trailer lines to each rebased commit message.
 > >
 > > Reject it if the user passes an option that requires the
 > > apply backend (git am) since it lacks message‑filter/trailer
 > > hook. otherwise we can just use the merge backend.
 > >
 > > Automatically set REBASE_FORCE when any trailer is supplied.
 > >
 > > And reject invalid input before user edit the interactive file.
 > 
 > s/edit/edits/
 > 
 > >
 > > Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
 > > ---
 > >  Documentation/git-rebase.adoc |  7 +++
 > >  builtin/rebase.c              | 89 +++++++++++++++++++++++++++++++++
 > >  sequencer.c                   | 13 +++++
 > >  sequencer.h                   |  4 +-
 > >  t/meson.build                 |  1 +
 > >  t/t3440-rebase-trailer.sh     | 94 +++++++++++++++++++++++++++++++++++
 > >  6 files changed, 207 insertions(+), 1 deletion(-)
 > >  create mode 100755 t/t3440-rebase-trailer.sh
 > >
 > > diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
 > > index 005caf6164..b2003b70d7 100644
 > > --- a/Documentation/git-rebase.adoc
 > > +++ b/Documentation/git-rebase.adoc
 > > @@ -488,6 +488,13 @@ See also INCOMPATIBLE OPTIONS below.
 > >      that if `--interactive` is given then only commits marked to be
 > >      picked, edited or reworded will have the trailer added.
 > >  +
 > > +--trailer <trailer>::
 > > +       Append the given trailer line(s) to every rebased commit
 > > +       message, processed via linkgit:git-interpret-trailers[1].
 > > +       When this option is present *rebase automatically implies*
 > > +       `--force-rebase` so that fast‑forwarded commits are also
 > > +       rewritten.
 > > +
 > 
 > You’ve cut off the second paragraph of `--signoff`.  This should be
 > added after `See also` below.
 
Thanks for catching this.

 > Probably also with an `=`:
 > 
 >     --trailer=<trailer>::
 > 

It would be added in v6; but both = and should work.

Regards,

Li​

[PATCH v4 10/29] rebase: inline trailer state paths

[Li Chen]

Simplified read_basic_state() by dropping the
temporary trailer path variables and calling
state_dir_path("trailer", opts) directly when
loading trailer arguments.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/rebase.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 3b001c0757..2a2674e375 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -442,8 +442,6 @@ static int read_basic_state(struct rebase_options *opts)
 	struct strbuf head_name = STRBUF_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct object_id oid;
-	const char trailer_state_name[] = "trailer";
-	const char *path = state_dir_path(trailer_state_name, opts);
 
 	if (!read_oneliner(&head_name, state_dir_path("head-name", opts),
 			   READ_ONELINER_WARN_MISSING) ||
@@ -512,7 +510,7 @@ static int read_basic_state(struct rebase_options *opts)
 
 	strbuf_release(&buf);
 
-	if (strbuf_read_file(&buf, path, 0) >= 0) {
+	if (strbuf_read_file(&buf, state_dir_path("trailer", opts), 0) >= 0) {
 		const char *p = buf.buf, *end = buf.buf + buf.len;
 
 		while (p < end) {
@@ -535,8 +533,6 @@ static int read_basic_state(struct rebase_options *opts)
 
 static int rebase_write_basic_state(struct rebase_options *opts)
 {
-	const char trailer_state_name[] = "trailer";
-
 	write_file(state_dir_path("head-name", opts), "%s",
 		   opts->head_name ? opts->head_name : "detached HEAD");
 	write_file(state_dir_path("onto", opts), "%s",
@@ -568,7 +564,7 @@ static int rebase_write_basic_state(struct rebase_options *opts)
 				strbuf_addstr(&buf, opts->trailer_args.v[i]);
 				strbuf_addch(&buf, '\n');
 		}
-		write_file(state_dir_path(trailer_state_name, opts),
+		write_file(state_dir_path("trailer", opts),
 				   "%s", buf.buf);
 		strbuf_release(&buf);
 	}
-- 
2.51.0

[PATCH v4 11/29] rebase: reuse buffer for trailer args

[Li Chen]

Reset the reusable buffer before reading trailer
arguments in read_basic_state() so the existing
allocation can be reused.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/rebase.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 2a2674e375..ff8dd9ec90 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -508,7 +508,7 @@ static int read_basic_state(struct rebase_options *opts)
 		opts->gpg_sign_opt = xstrdup(buf.buf);
 	}
 
-	strbuf_release(&buf);
+	strbuf_reset(&buf);
 
 	if (strbuf_read_file(&buf, state_dir_path("trailer", opts), 0) >= 0) {
 		const char *p = buf.buf, *end = buf.buf + buf.len;
-- 
2.51.0

[PATCH v4 12/29] rebase: drop redundant strbuf_release call

[Li Chen]

Removed the redundant strbuf_release() call in
read_basic_state() so the buffer is released once
even if strbuf_read_file() fails.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/rebase.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index ff8dd9ec90..51fb9388c7 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -524,7 +524,6 @@ static int read_basic_state(struct rebase_options *opts)
 
 			p = nl + 1;
 		}
-		strbuf_release(&buf);
 	}
 	strbuf_release(&buf);
 
-- 
2.51.0

[PATCH v4 13/29] rebase: skip stripping of --trailer option prefix

[Li Chen]

Removed redundant --trailer= prefix stripping in
validate_trailer_args_after_config() since OPT_STRVEC
already stores only the argument text.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/rebase.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 51fb9388c7..cc90980d7d 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1128,13 +1128,9 @@ static int validate_trailer_args_after_config(const struct strvec *cli_args,
 				       struct strbuf *err)
 {
 	for (size_t i = 0; i < cli_args->nr; i++) {
-		const char *raw = cli_args->v[i];
-		const char *txt; // Key[:=]Val
+		const char *txt = cli_args->v[i]; // Key[:=]Val
 		const char *sep;
 
-		if (!skip_prefix(raw, "--trailer=", &txt))
-			txt = raw;
-
 		if (!*txt) {
 			strbuf_addstr(err, _("empty --trailer argument"));
 			return -1;
-- 
2.51.0

[PATCH v4 14/29] rebase: die on invalid trailer args

[Li Chen]

This can simplify the error handle in
validate_trailer_args_after_config and
its caller.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/rebase.c | 26 +++++++-------------------
 1 file changed, 7 insertions(+), 19 deletions(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index cc90980d7d..872945a897 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1124,29 +1124,22 @@ static int check_exec_cmd(const char *cmd)
 	return 0;
 }
 
-static int validate_trailer_args_after_config(const struct strvec *cli_args,
-				       struct strbuf *err)
+static void validate_trailer_args_after_config(const struct strvec *cli_args)
 {
 	for (size_t i = 0; i < cli_args->nr; i++) {
 		const char *txt = cli_args->v[i]; // Key[:=]Val
 		const char *sep;
 
-		if (!*txt) {
-			strbuf_addstr(err, _("empty --trailer argument"));
-			return -1;
-		}
+		if (!*txt)
+			die(_("empty --trailer argument"));
 
 		sep = strpbrk(txt, ":=");
 
 		/* there must be key bfore seperator */
-		if (sep && sep == txt) {
-			strbuf_addf(err,
-				    _("invalid trailer '%s': missing key before separator"),
-				    txt);
-			return -1;
-		}
+		if (sep && sep == txt)
+			die(_("invalid trailer '%s': missing key before separator"),
+			    txt);
 	}
-	return 0;
 }
 
 int cmd_rebase(int argc,
@@ -1353,13 +1346,8 @@ int cmd_rebase(int argc,
 			     builtin_rebase_usage, 0);
 
 	if (options.trailer_args.nr) {
-		struct strbuf err = STRBUF_INIT;
-
-		if (validate_trailer_args_after_config(&options.trailer_args, &err))
-			die("%s", err.buf);
-
+		validate_trailer_args_after_config(&options.trailer_args);
 		options.flags |= REBASE_FORCE;
-		strbuf_release(&err);
 	}
 
 	if (preserve_merges_selected)
-- 
2.51.0

[PATCH v4 15/29] rebase: validate trailers with configured separators

[Li Chen]

Moved validate_trailer_args_after_config() into
trailer.c so trailer argument validation reuses
find_separator() and respects configured separators.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 builtin/rebase.c | 18 ------------------
 trailer.c        | 25 +++++++++++++++++++++++++
 trailer.h        |  2 ++
 3 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 872945a897..a88abe08b4 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1124,24 +1124,6 @@ static int check_exec_cmd(const char *cmd)
 	return 0;
 }
 
-static void validate_trailer_args_after_config(const struct strvec *cli_args)
-{
-	for (size_t i = 0; i < cli_args->nr; i++) {
-		const char *txt = cli_args->v[i]; // Key[:=]Val
-		const char *sep;
-
-		if (!*txt)
-			die(_("empty --trailer argument"));
-
-		sep = strpbrk(txt, ":=");
-
-		/* there must be key bfore seperator */
-		if (sep && sep == txt)
-			die(_("invalid trailer '%s': missing key before separator"),
-			    txt);
-	}
-}
-
 int cmd_rebase(int argc,
 	       const char **argv,
 	       const char *prefix,
diff --git a/trailer.c b/trailer.c
index b0ad7dc5c3..5ff518b436 100644
--- a/trailer.c
+++ b/trailer.c
@@ -7,6 +7,7 @@
 #include "string-list.h"
 #include "run-command.h"
 #include "commit.h"
+#include "strvec.h"
 #include "trailer.h"
 #include "list.h"
 #include "wrapper.h"
@@ -773,6 +774,30 @@ void parse_trailers_from_command_line_args(struct list_head *arg_head,
 	free(cl_separators);
 }
 
+void validate_trailer_args_after_config(const struct strvec *cli_args)
+{
+	char *cl_separators;
+
+	trailer_config_init();
+
+	cl_separators = xstrfmt("=%s", separators);
+
+	for (size_t i = 0; i < cli_args->nr; i++) {
+		const char *txt = cli_args->v[i];
+		ssize_t separator_pos;
+
+		if (!*txt)
+			die(_("empty --trailer argument"));
+
+		separator_pos = find_separator(txt, cl_separators);
+		if (separator_pos == 0)
+			die(_("invalid trailer '%s': missing key before separator"),
+		    txt);
+	}
+
+	free(cl_separators);
+}
+
 static const char *next_line(const char *str)
 {
 	const char *nl = strchrnul(str, '\n');
diff --git a/trailer.h b/trailer.h
index 01f711fb13..28719aa480 100644
--- a/trailer.h
+++ b/trailer.h
@@ -68,6 +68,8 @@ void parse_trailers_from_config(struct list_head *config_head);
 void parse_trailers_from_command_line_args(struct list_head *arg_head,
 					   struct list_head *new_trailer_head);
 
+void validate_trailer_args_after_config(const struct strvec *cli_args);
+
 void process_trailers_lists(struct list_head *head,
 			    struct list_head *arg_head);
 
-- 
2.51.0

[PATCH v4 16/29] sequencer: add trailers to message before writing file

[Li Chen]

Added trailer processing to the in-memory commit message
within do_pick_commit, ensuring fixup/squash commands
remain untouched before the message is written.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 sequencer.c | 19 ++++++++-----------
 trailer.c   |  4 ++--
 trailer.h   |  3 +++
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 5103ae786c..552e629e4f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2444,6 +2444,14 @@ static int do_pick_commit(struct repository *r,
 	if (opts->signoff && !is_fixup(command))
 		append_signoff(&ctx->message, 0, 0);
 
+	if (opts->trailer_args.nr && !is_fixup(command)) {
+		if (amend_strbuf_with_trailers(&ctx->message,
+					       &opts->trailer_args)) {
+			res = error(_("unable to add trailers to commit message"));
+			goto leave;
+		}
+	}
+
 	if (is_rebase_i(opts) && write_author_script(msg.message) < 0)
 		res = -1;
 	else if (!opts->strategy ||
@@ -2519,17 +2527,6 @@ static int do_pick_commit(struct repository *r,
 			oid_to_hex(&commit->object.oid), msg.subject);
 	} /* else allow == 0 and there's nothing special to do */
 
-	if (!res && opts->trailer_args.nr && !drop_commit) {
-		const char *trailer_file =
-			msg_file ? msg_file : git_path_merge_msg(r);
-
-		if (amend_file_with_trailers(trailer_file,
-						&opts->trailer_args)) {
-			res = error(_("unable to add trailers to commit message"));
-			goto leave;
-		}
-	}
-
 	if (!opts->no_commit && !drop_commit) {
 		if (author || command == TODO_REVERT || (flags & AMEND_MSG))
 			res = do_commit(r, msg_file, author, reflog_action,
diff --git a/trailer.c b/trailer.c
index 5ff518b436..fb691c6400 100644
--- a/trailer.c
+++ b/trailer.c
@@ -1250,8 +1250,8 @@ void trailer_iterator_release(struct trailer_iterator *iter)
 	strbuf_release(&iter->key);
 }
 
-static int amend_strbuf_with_trailers(struct strbuf *buf,
-									  const struct strvec *trailer_args)
+int amend_strbuf_with_trailers(struct strbuf *buf,
+       const struct strvec *trailer_args)
 {
 	struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
 	LIST_HEAD(new_trailer_head);
diff --git a/trailer.h b/trailer.h
index 28719aa480..e4b1de855e 100644
--- a/trailer.h
+++ b/trailer.h
@@ -197,6 +197,9 @@ int trailer_iterator_advance(struct trailer_iterator *iter);
  */
 void trailer_iterator_release(struct trailer_iterator *iter);
 
+int amend_strbuf_with_trailers(struct strbuf *buf,
+       const struct strvec *trailer_args);
+
 /*
  * Augment a file to add trailers to it (similar to 'git interpret-trailers').
  * Returns 0 on success or a non-zero error code on failure.
-- 
2.51.0

Re: [PATCH v4 16/29] sequencer: add trailers to message before writing file

[Kristoffer Haugsbakk]

On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
> Added trailer processing to the in-memory commit message
> within do_pick_commit, ensuring fixup/squash commands
> remain untouched before the message is written.
>
> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
> ---
>  sequencer.c | 19 ++++++++-----------
>  trailer.c   |  4 ++--
>  trailer.h   |  3 +++
>  3 files changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/sequencer.c b/sequencer.c
> index 5103ae786c..552e629e4f 100644
> --- a/sequencer.c
> +++ b/sequencer.c
>[snip]
> -static int amend_strbuf_with_trailers(struct strbuf *buf,
> -									  const struct strvec *trailer_args)

Weird indentation.  This looks like it needs clang-format.

> +int amend_strbuf_with_trailers(struct strbuf *buf,
> +       const struct strvec *trailer_args)
>  {
>[snip]

[PATCH v4 17/29] tests: t3440: create expect files at point of use

[Li Chen]

Created the expected trailer files within
the individual rebase tests that use them,
simplifying the shared history setup and
avoiding unused fixtures.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index c08a9c4abf..0c0185d058 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -26,14 +26,7 @@ test_expect_success 'setup repo with a small history' '
 	git checkout -b conflict-branch first &&
 	test_commit file-2 file-2 &&
 	test_commit conflict file &&
-	test_commit third file &&
-	ident="$GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>" &&
-	create_expect initial-signed  "Initial empty commit" &&
-	create_expect first-signed    "first"                 &&
-	create_expect second-signed   "second"                &&
-	create_expect file2-signed    "file-2"                &&
-	create_expect third-signed    "third"                 &&
-	create_expect conflict-signed "conflict"
+	test_commit third file
 '
 
 test_expect_success 'apply backend is rejected with --trailer' '
@@ -74,6 +67,7 @@ test_expect_success 'multiple Signed-off-by trailers all preserved' '
 '
 
 test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
+	create_expect file2-signed "file-2" &&
 	git reset --hard third &&
 	test_must_fail git rebase -m \
 		--trailer "Reviewed-by: Dev <dev@example.com>" \
@@ -85,6 +79,8 @@ test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
 '
 
 test_expect_success 'rebase --root --trailer updates every commit' '
+	create_expect initial-signed "Initial empty commit" &&
+	create_expect first-signed "first" &&
 	git checkout first &&
 	git rebase --root --keep-empty \
 		--trailer "Reviewed-by: Dev <dev@example.com>" &&
-- 
2.51.0

Re: [PATCH v4 17/29] tests: t3440: create expect files at point of use

[Kristoffer Haugsbakk]

Now you start to change the test suite/file that you created for this
series.  There shouldn’t be a need to do a test file-only patch/commit
for a fresh series.

I saw in one of your patches that you removed `--keep-empty` from a test
because “that is the default”.  I also saw Phillip’s comment somewhere
that said the same thing.

The goal with maturing series is not to add patches on top in each round
(if that’s what you are doing).  It is to recreate them as if the series
was perfectly written to begin with; if one patch introduces
`--trailers` and a test file, then there should be no need with
follow-up patches that improve the test file style, refactors it, and
so on.

> [PATCH v4 17/29] tests: t3440: create expect files at point of use

`t3440` is enough.

On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
> Created the expected trailer files within
> the individual rebase tests that use them,
> simplifying the shared history setup and
> avoiding unused fixtures.

The max line length (for prose) is 72 and I don’t know of a minimum
(41 here).

>
> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
> ---
>  t/t3440-rebase-trailer.sh | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
>[snip]

Re: [PATCH v4 17/29] tests: t3440: create expect files at point of use

[Li Chen]

Hi Kristoffer,

Thanks for the review suggestions! I'll address them in the next version.

 ---- On Wed, 15 Oct 2025 04:41:33 +0800  Kristoffer Haugsbakk <kristofferhaugsbakk@fastmail.com> wrote --- 
 > Now you start to change the test suite/file that you created for this
 > series.  There shouldn’t be a need to do a test file-only patch/commit
 > for a fresh series.
 > 
 > I saw in one of your patches that you removed `--keep-empty` from a test
 > because “that is the default”.  I also saw Phillip’s comment somewhere
 > that said the same thing.
 > 
 > The goal with maturing series is not to add patches on top in each round
 > (if that’s what you are doing).  It is to recreate them as if the series
 > was perfectly written to begin with; if one patch introduces
 > `--trailers` and a test file, then there should be no need with
 > follow-up patches that improve the test file style, refactors it, and
 > so on.

Thanks for the tip. I split the changes into separate commits to ease review,
 as Phillip suggested in https://lore.kernel.org/git/d4c9f082-52be-48d9-b817-fcb8a72e1bd7@gmail.com/.

It seems I may have overdone it? If so, I'll try for a better balance in the next version.

Li​

Re: [PATCH v4 17/29] tests: t3440: create expect files at point of use

[Kristoffer Haugsbakk]

On Wed, Oct 15, 2025, at 15:58, Li Chen wrote:
>[snip]
>  > (if that’s what you are doing).  It is to recreate them as if the
> series
>  > was perfectly written to begin with; if one patch introduces
>  > `--trailers` and a test file, then there should be no need with
>  > follow-up patches that improve the test file style, refactors it, and
>  > so on.
>
> Thanks for the tip. I split the changes into separate commits to ease
> review,
>  as Phillip suggested in
> https://lore.kernel.org/git/d4c9f082-52be-48d9-b817-fcb8a72e1bd7@gmail.com/.
>
> It seems I may have overdone it? If so, I'll try for a better balance
> in the next version.

Thank you. It seems like I should have skimmed the previous rounds
more carefully. :)

Cheers

Re: [PATCH v4 17/29] tests: t3440: create expect files at point of use

[Phillip Wood]

On 15/10/2025 14:58, Li Chen wrote:
> Hi Kristoffer,
> 
> Thanks for the review suggestions! I'll address them in the next version.
> 
>   ---- On Wed, 15 Oct 2025 04:41:33 +0800  Kristoffer Haugsbakk <kristofferhaugsbakk@fastmail.com> wrote ---
>   > Now you start to change the test suite/file that you created for this
>   > series.  There shouldn’t be a need to do a test file-only patch/commit
>   > for a fresh series.
>   >
>   > I saw in one of your patches that you removed `--keep-empty` from a test
>   > because “that is the default”.  I also saw Phillip’s comment somewhere
>   > that said the same thing.
>   >
>   > The goal with maturing series is not to add patches on top in each round
>   > (if that’s what you are doing).  It is to recreate them as if the series
>   > was perfectly written to begin with; if one patch introduces
>   > `--trailers` and a test file, then there should be no need with
>   > follow-up patches that improve the test file style, refactors it, and
>   > so on.
> 
> Thanks for the tip. I split the changes into separate commits to ease review,
>   as Phillip suggested in https://lore.kernel.org/git/d4c9f082-52be-48d9-b817-fcb8a72e1bd7@gmail.com/.
> 
> It seems I may have overdone it? If so, I'll try for a better balance in the next version.
I asked that you did not refactor code at the same time as you moved it. 
I was expecting a handful of patches, not twenty-nine. The point that 
Kristoffer makes about this patch is perfectly valid - you add a new 
test and then correct it in a later patch. Instead you should correct 
the test where it is introduced as Kirstoffer suggested. Looking at the 
first patch in this series there seems to have been some 
miscommunication because it has exactly the same problem as V3. The code 
that is moved from builtin/interpret-trailers.c to trailer.c is heavily 
refactored at the same time. Variable names are changed and the code is 
rearranged so that "git diff --color-moved 
--color-moved-ws=ignore-indentation-change" detects barely any moved 
lines. I'll try and leave some more detailed feedback on the first few 
patches of V5 in the next few days.

Thanks

Phillip

Re: [PATCH v4 17/29] tests: t3440: create expect files at point of use

[Li Chen]

Hi Phillip,

 ---- On Thu, 23 Oct 2025 17:04:34 +0800  Phillip Wood <phillip.wood123@gmail.com> wrote --- 
 > On 15/10/2025 14:58, Li Chen wrote:
 > > Hi Kristoffer,
 > > 
 > > Thanks for the review suggestions! I'll address them in the next version.
 > > 
 > >   ---- On Wed, 15 Oct 2025 04:41:33 +0800  Kristoffer Haugsbakk <kristofferhaugsbakk@fastmail.com> wrote ---
 > >   > Now you start to change the test suite/file that you created for this
 > >   > series.  There shouldn’t be a need to do a test file-only patch/commit
 > >   > for a fresh series.
 > >   >
 > >   > I saw in one of your patches that you removed `--keep-empty` from a test
 > >   > because “that is the default”.  I also saw Phillip’s comment somewhere
 > >   > that said the same thing.
 > >   >
 > >   > The goal with maturing series is not to add patches on top in each round
 > >   > (if that’s what you are doing).  It is to recreate them as if the series
 > >   > was perfectly written to begin with; if one patch introduces
 > >   > `--trailers` and a test file, then there should be no need with
 > >   > follow-up patches that improve the test file style, refactors it, and
 > >   > so on.
 > > 
 > > Thanks for the tip. I split the changes into separate commits to ease review,
 > >   as Phillip suggested in https://lore.kernel.org/git/d4c9f082-52be-48d9-b817-fcb8a72e1bd7@gmail.com/.
 > > 
 > > It seems I may have overdone it? If so, I'll try for a better balance in the next version.
 > I asked that you did not refactor code at the same time as you moved it. 
 > I was expecting a handful of patches, not twenty-nine. The point that 
 > Kristoffer makes about this patch is perfectly valid - you add a new 
 > test and then correct it in a later patch. Instead you should correct 
 > the test where it is introduced as Kirstoffer suggested. Looking at the 
 > first patch in this series there seems to have been some 
 > miscommunication because it has exactly the same problem as V3. The code 
 > that is moved from builtin/interpret-trailers.c to trailer.c is heavily 
 > refactored at the same time. Variable names are changed and the code is 
 > rearranged so that "git diff --color-moved 
 > --color-moved-ws=ignore-indentation-change" detects barely any moved 
 > lines. I'll try and leave some more detailed feedback on the first few 
 > patches of V5 in the next few days.

I mistakenly misunderstood that you meant changes between each patchset version should be reflected by adding new patches. 
Now I understand that you mean refactoring the original code needs to be reflected in new patches for review. Thank you very 
Thank you for telling me about --color-moved, and I found that git log also has this parameter. This option is very amazing.
 I will do as you requested in the next version. 

I sincerely apologize for the misunderstanding and wasted time.

Regards,
Li​

Re: [PATCH v4 17/29] tests: t3440: create expect files at point of use

[Phillip Wood]

Hi Li

On 28/10/2025 10:26, Li Chen wrote:
> 
> I mistakenly misunderstood that you meant changes between each patchset version should be reflected by adding new patches.
> Now I understand that you mean refactoring the original code needs to be reflected in new patches for review. Thank you very
> Thank you for telling me about --color-moved, and I found that git log also has this parameter. This option is very amazing.
>   I will do as you requested in the next version.
> 
> I sincerely apologize for the misunderstanding and wasted time.

Don't worry, I left some more detailled comments on v5 at 
https://lore.kernel.org/git/7d12b046-365f-441c-af8e-8a39d61efbbd@gmail.com 
please do feel free to let me know if you have any questions.

Thanks

Phillip

[PATCH v4 18/29] tests: t3440: check apply backend error includes option

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Updated the rebase trailer test to assert that
the apply-backend error explicitly includes the
--trailer option in its message while retaining
the existing backend check.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 0c0185d058..6f1a062e8f 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -34,7 +34,7 @@ test_expect_success 'apply backend is rejected with --trailer' '
 	test_expect_code 128 \
 	git rebase --apply --trailer "Reviewed-by: Dev <dev@example.com>" \
 				HEAD^ 2>err &&
-	test_grep "requires the merge backend" err &&
+	test_grep "fatal: --trailer requires the merge backend" err &&
 	test_cmp_rev HEAD $head_before
 '
 
-- 
2.51.0

[PATCH v4 19/29] tests: t3440: use test_commit_message for trailer checks

[Li Chen]

Replaced the pipeline-based trailer assertions with
explicit expectations verified by test_commit_message,
ensuring the rebase trailer tests catch git command
failures reliably.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 6f1a062e8f..16b059c2c3 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -52,18 +52,28 @@ test_expect_success 'reject trailer with missing key before separator' '
 
 test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last' '
 	git reset --hard third &&
-	git -c trailer.Bug.ifexists=replace -c trailer.Bug.ifmissing=add rebase -m --trailer "Bug: 123" --trailer "Bug: 456" HEAD~1 &&
-	git cat-file commit HEAD | grep "^Bug: 456" &&
-	git cat-file commit HEAD | grep -v "^Bug: 123"
+	git -c trailer.Bug.ifexists=replace -c trailer.Bug.ifmissing=add \
+		rebase -m --trailer "Bug: 123" --trailer "Bug: 456" HEAD~1 &&
+	cat >expect <<-\EOF &&
+	third
+
+	Bug: 456
+	EOF
+	test_commit_message HEAD expect
 '
 
 test_expect_success 'multiple Signed-off-by trailers all preserved' '
 	git reset --hard third &&
 	git rebase -m \
-		--trailer "Signed-off-by: Dev A <a@ex.com>" \
-		--trailer "Signed-off-by: Dev B <b@ex.com>" HEAD~1 &&
-	git cat-file commit HEAD | grep -c "^Signed-off-by:" >count &&
-	test "$(cat count)" = 2   # two new commits
+			--trailer "Signed-off-by: Dev A <a@ex.com>" \
+			--trailer "Signed-off-by: Dev B <b@ex.com>" HEAD~1 &&
+	cat >expect <<-\EOF &&
+	third
+
+	Signed-off-by: Dev A <a@ex.com>
+	Signed-off-by: Dev B <b@ex.com>
+	EOF
+	test_commit_message HEAD expect
 '
 
 test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
-- 
2.51.0

[PATCH v4 20/29] tests: t3440: drop redundant resets and pass branch to rebase where needed

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Stop hard-resetting to third in these tests. Where the branch matters,
invoke git rebase -m ... HEAD~1 third to make the target explicit and
preserve the original semantics.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 16b059c2c3..4f313654d6 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -39,21 +39,18 @@ test_expect_success 'apply backend is rejected with --trailer' '
 '
 
 test_expect_success 'reject empty --trailer argument' '
-	git reset --hard third &&
 	test_expect_code 128 git rebase -m --trailer "" HEAD^ 2>err &&
 	test_grep "empty --trailer" err
 '
 
 test_expect_success 'reject trailer with missing key before separator' '
-	git reset --hard third &&
 	test_expect_code 128 git rebase -m --trailer ": no-key" HEAD^ 2>err &&
 	test_grep "missing key before separator" err
 '
 
 test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last' '
-	git reset --hard third &&
 	git -c trailer.Bug.ifexists=replace -c trailer.Bug.ifmissing=add \
-		rebase -m --trailer "Bug: 123" --trailer "Bug: 456" HEAD~1 &&
+		rebase -m --trailer "Bug: 123" --trailer "Bug: 456" HEAD~1 third &&
 	cat >expect <<-\EOF &&
 	third
 
@@ -63,10 +60,9 @@ test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last'
 '
 
 test_expect_success 'multiple Signed-off-by trailers all preserved' '
-	git reset --hard third &&
 	git rebase -m \
 			--trailer "Signed-off-by: Dev A <a@ex.com>" \
-			--trailer "Signed-off-by: Dev B <b@ex.com>" HEAD~1 &&
+			--trailer "Signed-off-by: Dev B <b@ex.com>" HEAD~1 third &&
 	cat >expect <<-\EOF &&
 	third
 
@@ -78,7 +74,6 @@ test_expect_success 'multiple Signed-off-by trailers all preserved' '
 
 test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
 	create_expect file2-signed "file-2" &&
-	git reset --hard third &&
 	test_must_fail git rebase -m \
 		--trailer "Reviewed-by: Dev <dev@example.com>" \
 		second third &&
-- 
2.51.0

[PATCH v4 21/29] tests: t3440: assert trailer on HEAD after conflict rebase

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Switch the test to check the trailer on HEAD (not HEAD~2) and build the
expected message for "third", matching the rebased tip after conflicts.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 4f313654d6..e1a3d2e3eb 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -73,14 +73,14 @@ test_expect_success 'multiple Signed-off-by trailers all preserved' '
 '
 
 test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
-	create_expect file2-signed "file-2" &&
+	create_expect third-signed "third" &&
 	test_must_fail git rebase -m \
 		--trailer "Reviewed-by: Dev <dev@example.com>" \
 		second third &&
 	git checkout --theirs file &&
 	git add file &&
 	git rebase --continue &&
-	test_commit_message HEAD~2 file2-signed
+	test_commit_message HEAD third-signed
 '
 
 test_expect_success 'rebase --root --trailer updates every commit' '
-- 
2.51.0

[PATCH v4 22/29] rebase: persist --trailer options across restarts

[Li Chen]

t3440 showed rebase -m loses trailers after conflicts.
Each --continue spawns a fresh replay_opts without trailer_args.
Serialize them into rebase-merge/trailer so new runs reload them.
This keeps the user requested trailers intact when resuming.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 sequencer.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index 552e629e4f..c02364cfce 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -209,6 +209,7 @@ static GIT_PATH_FUNC(rebase_path_reschedule_failed_exec, "rebase-merge/reschedul
 static GIT_PATH_FUNC(rebase_path_no_reschedule_failed_exec, "rebase-merge/no-reschedule-failed-exec")
 static GIT_PATH_FUNC(rebase_path_drop_redundant_commits, "rebase-merge/drop_redundant_commits")
 static GIT_PATH_FUNC(rebase_path_keep_redundant_commits, "rebase-merge/keep_redundant_commits")
+static GIT_PATH_FUNC(rebase_path_trailer, "rebase-merge/trailer")
 
 /*
  * A 'struct replay_ctx' represents the private state of the sequencer.
@@ -3244,6 +3245,17 @@ static int read_populate_opts(struct replay_opts *opts)
 
 		read_strategy_opts(opts, &buf);
 		strbuf_reset(&buf);
+		if (strbuf_read_file(&buf, rebase_path_trailer(), 0) >= 0) {
+			char *p = buf.buf, *nl;
+
+			while ((nl = strchr(p, '\n'))) {
+				*nl = '\0';
+				if (*p)
+					strvec_push(&opts->trailer_args, p);
+				p = nl + 1;
+			}
+			strbuf_reset(&buf);
+		}
 
 		if (read_oneliner(&ctx->current_fixups,
 				  rebase_path_current_fixups(),
@@ -3338,6 +3350,14 @@ int write_basic_state(struct replay_opts *opts, const char *head_name,
 		write_file(rebase_path_reschedule_failed_exec(), "%s", "");
 	else
 		write_file(rebase_path_no_reschedule_failed_exec(), "%s", "");
+	if (opts->trailer_args.nr) {
+		struct strbuf buf = STRBUF_INIT;
+
+		for (size_t i = 0; i < opts->trailer_args.nr; i++)
+			strbuf_addf(&buf, "%s\n", opts->trailer_args.v[i]);
+		write_file(rebase_path_trailer(), "%s", buf.buf);
+		strbuf_release(&buf);
+	}
 
 	return 0;
 }
-- 
2.51.0

[PATCH v4 23/29] tests: t3440: remove redundant --keep-empty

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

--keep-empty is the default these days so
we can drop that.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index e1a3d2e3eb..2315a0c86c 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -87,7 +87,7 @@ test_expect_success 'rebase --root --trailer updates every commit' '
 	create_expect initial-signed "Initial empty commit" &&
 	create_expect first-signed "first" &&
 	git checkout first &&
-	git rebase --root --keep-empty \
+	git rebase --root \
 		--trailer "Reviewed-by: Dev <dev@example.com>" &&
 	test_commit_message HEAD   first-signed &&
 	test_commit_message HEAD^  initial-signed
-- 
2.51.0

[PATCH v4 24/29] tests: t3440: use helper for trailer checks

[Li Chen]

Introduce expect_trailer_msg() to wrap test_commit_message
and dedupe the trailer via REVIEWED_BY_TRAILER.
Drop create_expect and temp files. In the conflict case,
assert on HEAD (rebased "third") instead of HEAD~2. Update
--apply rejection and --root tests to use the helper.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 2315a0c86c..36f11f579e 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -11,11 +11,13 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-rebase.sh # test_commit_message, helpers
 
-create_expect() {
-	cat >"$1" <<-EOF
+REVIEWED_BY_TRAILER="Reviewed-by: Dev <dev@example.com>"
+
+expect_trailer_msg() {
+	test_commit_message "$1" <<-EOF
 		$2
 
-		Reviewed-by: Dev <dev@example.com>
+		${3:-$REVIEWED_BY_TRAILER}
 	EOF
 }
 
@@ -32,7 +34,7 @@ test_expect_success 'setup repo with a small history' '
 test_expect_success 'apply backend is rejected with --trailer' '
 	head_before=$(git rev-parse HEAD) &&
 	test_expect_code 128 \
-	git rebase --apply --trailer "Reviewed-by: Dev <dev@example.com>" \
+	git rebase --apply --trailer "$REVIEWED_BY_TRAILER" \
 				HEAD^ 2>err &&
 	test_grep "fatal: --trailer requires the merge backend" err &&
 	test_cmp_rev HEAD $head_before
@@ -73,23 +75,20 @@ test_expect_success 'multiple Signed-off-by trailers all preserved' '
 '
 
 test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
-	create_expect third-signed "third" &&
 	test_must_fail git rebase -m \
-		--trailer "Reviewed-by: Dev <dev@example.com>" \
+		--trailer "$REVIEWED_BY_TRAILER" \
 		second third &&
 	git checkout --theirs file &&
 	git add file &&
 	git rebase --continue &&
-	test_commit_message HEAD third-signed
+	expect_trailer_msg HEAD "third"
 '
 
 test_expect_success 'rebase --root --trailer updates every commit' '
-	create_expect initial-signed "Initial empty commit" &&
-	create_expect first-signed "first" &&
 	git checkout first &&
 	git rebase --root \
-		--trailer "Reviewed-by: Dev <dev@example.com>" &&
-	test_commit_message HEAD   first-signed &&
-	test_commit_message HEAD^  initial-signed
+		--trailer "$REVIEWED_BY_TRAILER" &&
+	expect_trailer_msg HEAD  "first" &&
+	expect_trailer_msg HEAD^ "Initial empty commit"
 '
 test_done
-- 
2.51.0

[PATCH v4 25/29] tests: t3440: test --trailer without values

[Li Chen]

Added a regression test to ensure git
rebase --trailer accepts trailers without
values while preserving the separator’s
trailing space in the recorded message.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 36f11f579e..df121efd0e 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -50,6 +50,16 @@ test_expect_success 'reject trailer with missing key before separator' '
 	test_grep "missing key before separator" err
 '
 
+test_expect_success 'allow trailer with missing value after separator' '
+	git rebase -m --trailer "Acked-by:" HEAD~1 third &&
+	cat >expect <<-\EOF &&
+	third
+
+	Acked-by: 
+	EOF
+	test_commit_message HEAD expect
+'
+
 test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last' '
 	git -c trailer.Bug.ifexists=replace -c trailer.Bug.ifmissing=add \
 		rebase -m --trailer "Bug: 123" --trailer "Bug: 456" HEAD~1 third &&
-- 
2.51.0

Re: [PATCH v4 25/29] tests: t3440: test --trailer without values

[Kristoffer Haugsbakk]

On Tue, Oct 14, 2025, at 14:24, Li Chen wrote:
> Added a regression test to ensure git
> rebase --trailer accepts trailers without
> values while preserving the separator’s
> trailing space in the recorded message.

See “imperative-mood” in `Documentation/SubmittingPatches`.
Something like:

    Add a regression test to ensure

>
> Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
> ---
>  t/t3440-rebase-trailer.sh | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
> index 36f11f579e..df121efd0e 100755
> --- a/t/t3440-rebase-trailer.sh
> +++ b/t/t3440-rebase-trailer.sh
> @@ -50,6 +50,16 @@ test_expect_success 'reject trailer with missing key
> before separator' '
>  	test_grep "missing key before separator" err
>  '
>
> +test_expect_success 'allow trailer with missing value after separator'
> '
> +	git rebase -m --trailer "Acked-by:" HEAD~1 third &&
> +	cat >expect <<-\EOF &&
> +	third
> +
> +	Acked-by:

This adds a trailing space to the source which will make
`ci/check-whitespace.sh` fail.  I think you are supposed to do something
similar to what is done in `t/t4124-apply-ws-rule.sh`.  Namely to use
some placeholder character like `_`:

    Acked-by:_

Together with:

    sed -e "s/_/ /g"

I could also imagine that a variable like `${SP}` might have worked
together with `-EOF` similar to single quote:

   t/test-lib.sh:SQ=\'

But `t/test-lib.sh` does not seem to have that.  (Although it does have
`LF` (line feed)).

> +	EOF
>[snip]

[PATCH v4 26/29] tests: t3440: convert ex.com to example.com

[Li Chen]

From: Li Chen <chenl311@chinatelecom.cn>

Lets use example.com here rather than some
random domain that might actually exist.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index df121efd0e..dd703b0eb7 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -73,13 +73,13 @@ test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last'
 
 test_expect_success 'multiple Signed-off-by trailers all preserved' '
 	git rebase -m \
-			--trailer "Signed-off-by: Dev A <a@ex.com>" \
-			--trailer "Signed-off-by: Dev B <b@ex.com>" HEAD~1 third &&
+			--trailer "Signed-off-by: Dev A <a@example.com>" \
+			--trailer "Signed-off-by: Dev B <b@example.com>" HEAD~1 third &&
 	cat >expect <<-\EOF &&
 	third
 
-	Signed-off-by: Dev A <a@ex.com>
-	Signed-off-by: Dev B <b@ex.com>
+	Signed-off-by: Dev A <a@example.com>
+	Signed-off-by: Dev B <b@example.com>
 	EOF
 	test_commit_message HEAD expect
 '
-- 
2.51.0

[PATCH v4 27/29] tests: t3440: ensure trailers persist after rebase continue

[Li Chen]

Rebuilt the conflict test branch, added a fourth commit,
and asserted that both the conflicted and subsequent commits
receive the --trailer data in t/t3440-rebase-trailer.sh.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index dd703b0eb7..7a2ddb440e 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -85,13 +85,16 @@ test_expect_success 'multiple Signed-off-by trailers all preserved' '
 '
 
 test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
+	git checkout -B conflict-branch third &&
+	test_commit fourth file &&
 	test_must_fail git rebase -m \
-		--trailer "$REVIEWED_BY_TRAILER" \
-		second third &&
+			--trailer "$REVIEWED_BY_TRAILER" \
+			second &&
 	git checkout --theirs file &&
 	git add file &&
 	git rebase --continue &&
-	expect_trailer_msg HEAD "third"
+	expect_trailer_msg HEAD "fourth" &&
+	expect_trailer_msg HEAD^ "third"
 '
 
 test_expect_success 'rebase --root --trailer updates every commit' '
-- 
2.51.0

[PATCH v4 28/29] tests: t3440: exercise trailer config mapping

[Li Chen]

Updated the rebase --root --trailer test
to exercise trailer.review.key configuration
and the --trailer= CLI form that uses an
equals separator, ensuring we still add the
expected Reviewed-by trailer.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 t/t3440-rebase-trailer.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index 7a2ddb440e..ca0619655e 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -99,8 +99,8 @@ test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
 
 test_expect_success 'rebase --root --trailer updates every commit' '
 	git checkout first &&
-	git rebase --root \
-		--trailer "$REVIEWED_BY_TRAILER" &&
+	git -c trailer.review.key=Reviewed-by rebase --root \
+		--trailer=review="Dev <dev@example.com>" &&
 	expect_trailer_msg HEAD  "first" &&
 	expect_trailer_msg HEAD^ "Initial empty commit"
 '
-- 
2.51.0

[PATCH v4 29/29] sequencer: honor --trailer with fixup -C

[Li Chen]

Add an interactive rebase test that exercises
todo lists containing fixup and fixup -C commands,
and teach append_squash_message() to append trailers
when replacing the commit message.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 sequencer.c               |  4 ++++
 t/t3440-rebase-trailer.sh | 27 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index c02364cfce..fbf35cb474 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2027,6 +2027,10 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 		if (opts->signoff)
 			append_signoff(buf, 0, 0);
 
+		if (opts->trailer_args.nr &&
+			amend_strbuf_with_trailers(buf, &opts->trailer_args))
+			return error(_("unable to add trailers to commit message"));
+
 		if ((command == TODO_FIXUP) &&
 		    (flag & TODO_REPLACE_FIXUP_MSG) &&
 		    (file_exists(rebase_path_fixup_msg()) ||
diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
index ca0619655e..d0526ea0e9 100755
--- a/t/t3440-rebase-trailer.sh
+++ b/t/t3440-rebase-trailer.sh
@@ -97,6 +97,33 @@ test_expect_success 'rebase -m --trailer adds trailer after conflicts' '
 	expect_trailer_msg HEAD^ "third"
 '
 
+test_expect_success '--trailer handles fixup commands in todo list' '
+	git checkout -B fixup-trailer HEAD &&
+	test_commit fixup-base base &&
+	test_commit fixup-second second &&
+	first_short=$(git rev-parse --short fixup-base) &&
+	second_short=$(git rev-parse --short fixup-second) &&
+	cat >todo <<EOF &&
+pick $first_short fixup-base
+fixup $second_short fixup-second
+EOF
+	(
+		set_replace_editor todo &&
+		git rebase -i --trailer "$REVIEWED_BY_TRAILER" HEAD~2
+	) &&
+	expect_trailer_msg HEAD "fixup-base" &&
+	git reset --hard fixup-second &&
+	cat >todo <<EOF &&
+pick $first_short fixup-base
+fixup -C $second_short fixup-second
+EOF
+	(
+		set_replace_editor todo &&
+		git rebase -i --trailer "$REVIEWED_BY_TRAILER" HEAD~2
+	) &&
+	expect_trailer_msg HEAD "fixup-second"
+'
+
 test_expect_success 'rebase --root --trailer updates every commit' '
 	git checkout first &&
 	git -c trailer.review.key=Reviewed-by rebase --root \
-- 
2.51.0

Re: [PATCH v4 00/29] rebase: support --trailer

[Li Chen]

Hi Phillip & Junio,

I apologize for the delay in sending out v4. I will respond to
and update the code in the following patchset (if needed)
 as soon as possible. 

My apologies!

 ---- On Tue, 14 Oct 2025 20:24:13 +0800  Li Chen <me@linux.beauty> wrote --- 
 > 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.
 > 
 > v4: fix all reviewer comments in v3. [2]
 > 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/
 > 
 > 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
 >   tests: t3440: create expect files at point of use
 >   tests: t3440: check apply backend error includes option
 >   tests: t3440: use test_commit_message for trailer checks
 >   tests: t3440: drop redundant resets and pass branch to rebase where
 >     needed
 >   tests: t3440: assert trailer on HEAD after conflict rebase
 >   rebase: persist --trailer options across restarts
 >   tests: t3440: remove redundant --keep-empty
 >   tests: t3440: use helper for trailer checks
 >   tests: t3440: test --trailer without values
 >   tests: t3440: convert ex.com to example.com
 >   tests: t3440: ensure trailers persist after rebase continue
 >   tests: t3440: exercise trailer config mapping
 >   sequencer: honor --trailer with fixup -C
 > 
 >  Documentation/git-rebase.adoc |   7 ++
 >  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, 411 insertions(+), 93 deletions(-)
 >  create mode 100755 t/t3440-rebase-trailer.sh
 > 
 > -- 
 > 2.51.0
 > 
 > 

Regards,

Li​