[PATCH v2] [GSOC] commit: add trailer command

From: ZheNing Hu <redacted>

Historically, Git has supported the 'Signed-off-by' commit trailer
using the '--signoff' and the '-s' option from the command line.
But users may need to provide richer trailer information from the
command line such as "Helped-by", "Reported-by", "Mentored-by",

Now use `--trailer <token>[(=|:)<value>]` pass the trailers to
`interpret-trailers` and generate trailers in commit messages.

Signed-off-by: ZheNing Hu <redacted>
---
    [GSOC] commit: provides multiple signatures from command line
    
    Now maintainers or developers can also use commit
    --trailer="Signed-off-by:commiter<email>" from the command line to
    provide trailers to commit messages. This solution may be more
    generalized than v1.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-901%2Fadlternative%2Fcommit-with-multiple-signatures-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-901/adlternative/commit-with-multiple-signatures-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/901

Range-diff vs v1:

 1:  e9389e72ac65 ! 1:  4c507d17db4f [GSOC] commit: provides multiple common signatures
     @@ Metadata
      Author: ZheNing Hu [off-list ref]
      
       ## Commit message ##
     -    [GSOC] commit: provides multiple common signatures
     +    [GSOC] commit: add trailer command
      
     -    Similar to "Helped-by", "Reported-by", "Reviewed-by", "Mentored-by"
     -    these signatures are often seen in git commit messages. After
     -    referring to the simple implementation of `commit --signoff`
     -    and `send-email -cc=" commiter <email>"`, I am considering
     -    whether to provide multiple signature parameters from the
     -    command line. I think this might help maintainers and
     -    developers directly uses the shell to provide these signatures
     -    instead of multiple times repetitive writing those trailers
     -    each time.
     +    Historically, Git has supported the 'Signed-off-by' commit trailer
     +    using the '--signoff' and the '-s' option from the command line.
     +    But users may need to provide richer trailer information from the
     +    command line such as "Helped-by", "Reported-by", "Mentored-by",
      
     -    To achieve this goal, i refactored the `append_signoff` design and
     -    provided `append_message` and `append_message_string_list` interfaces,
     -    providing new ways to generate those various signatures.
     -
     -    Users now can use `commit -H "helper <eamil>"` to generate "Helped-by" trailer,
     -    `commit -R "reviewer <eamil>"` to generate "Reviewed-by" trailer,
     -    `commit -r "reporter <eamil> "`to generate "Reported-by" trailer,
     -    `commit -M "mentor <eamil>"` to generate "Mentored-by" trailer.
     +    Now use `--trailer <token>[(=|:)<value>]` pass the trailers to
     +    `interpret-trailers` and generate trailers in commit messages.
      
          Signed-off-by: ZheNing Hu [off-list ref]
      
     @@ Documentation/git-commit.txt: SYNOPSIS
       	   [--date=<date>] [--cleanup=<mode>] [--[no-]status]
       	   [-i | -o] [--pathspec-from-file=<file> [--pathspec-file-nul]]
      -	   [-S[<keyid>]] [--] [<pathspec>...]
     -+	   [-S[<keyid>]] [--] [<pathspec>...] [(-H|--helped-by)=<address>...]
     -+	   [(-R|--reviewed-by)=<address>...] [(-r|--reported-by)=<address>...]
     -+	   [(-M|--mentored)=<address>...]
     ++	   [-S[<keyid>]] [--] [<pathspec>...] [(--trailer <token>[(=|:)<value>])...]
       
       DESCRIPTION
       -----------
     @@ Documentation/git-commit.txt: The `-m` option is mutually exclusive with `-c`, `
       
       include::signoff-option.txt[]
       
     -+-H=<address>...::
     -+--helped-by=<address>...::
     -+	Add one or more `Helped-by` trailer by the committer at the end of the commit
     -+	log message.
     -+
     -+-R=<address>...::
     -+--reviewed-by=<address>...::
     -+	Add one or more `Reviewed-by` trailer by the committer at the end of the commit
     -+	log message.
     -+
     -+-r=<address>...::
     -+--reported-by=<address>...::
     -+	Add one or more `Reported-by` trailer by the committer at the end of the commit
     -+	log message.
     -+
     -+-M=<address>...::
     -+--mentored-by=<address>...::
     -+	Add one or more `Mentored-by` trailer by the committer at the end of the commit
     -+	log message.
     ++--trailer <token>[(=|:)<value>]::
     ++	Specify a (<token>, <value>) pair that should be applied as a
     ++	trailer. (e.g.  `git commit --trailer "Signed-off-by:C O Mitter [off-list ref]" \
     ++	--trailer "Helped-by:C O Mitter [off-list ref]"`will add the "Signed-off" trailer
     ++	and the "Helped-by" trailer in the commit message.)
      +
       -n::
       --no-verify::
     @@ builtin/commit.c: static int config_commit_verbose = -1; /* unspecified */
       static int no_post_rewrite, allow_empty_message, pathspec_file_nul;
       static char *untracked_files_arg, *force_date, *ignore_submodule_arg, *ignored_arg;
       static char *sign_commit, *pathspec_from_file;
     -+static struct string_list helped_by = STRING_LIST_INIT_NODUP;
     -+static struct string_list mentored_by = STRING_LIST_INIT_NODUP;
     -+static struct string_list reviewed_by = STRING_LIST_INIT_NODUP;
     -+static struct string_list reported_by = STRING_LIST_INIT_NODUP;
     ++struct child_process run_trailer = CHILD_PROCESS_INIT;
     ++static const char *trailer;
       
       /*
        * The default commit message cleanup mode will remove the lines
     -@@ builtin/commit.c: static int prepare_to_commit(const char *index_file, const char *prefix,
     - 	if (signoff)
     - 		append_signoff(&sb, ignore_non_trailer(sb.buf, sb.len), 0);
     - 
     -+	if(helped_by.items)
     -+		append_message_string_list(&sb, "Helped-by: ", &helped_by, ignore_non_trailer(sb.buf, sb.len), 0);
     -+	if(reviewed_by.items)
     -+		append_message_string_list(&sb, "Reviewed-by: ", &reviewed_by, ignore_non_trailer(sb.buf, sb.len), 0);
     -+	if(reported_by.items)
     -+		append_message_string_list(&sb, "Reported-by: ", &reported_by, ignore_non_trailer(sb.buf, sb.len), 0);
     -+	if(mentored_by.items)
     -+		append_message_string_list(&sb, "Mentored-by: ", &mentored_by, ignore_non_trailer(sb.buf, sb.len), 0);
     -+
     -+	string_list_clear(&helped_by, 0);
     -+	string_list_clear(&reviewed_by, 0);
     -+	string_list_clear(&reported_by, 0);
     -+	string_list_clear(&mentored_by, 0);
     -+
     - 	if (fwrite(sb.buf, 1, sb.len, s->fp) < sb.len)
     - 		die_errno(_("could not write commit template"));
     +@@ builtin/commit.c: static struct strbuf message = STRBUF_INIT;
       
     -@@ builtin/commit.c: static int git_commit_config(const char *k, const char *v, void *cb)
     - 	return git_status_config(k, v, s);
     - }
     + static enum wt_status_format status_format = STATUS_FORMAT_UNSPECIFIED;
       
     -+static int help_callback(const struct option *opt, const char *arg, int unset)
     -+{
     -+	if (unset)
     -+		string_list_clear(&helped_by, 0);
     -+	else
     -+		string_list_append(&helped_by, arg);
     -+	return 0;
     -+}
     -+
     -+static int review_callback(const struct option *opt, const char *arg, int unset)
     ++static int opt_pass_trailer(const struct option *opt, const char *arg, int unset)
      +{
     -+	if (unset)
     -+		string_list_clear(&reviewed_by, 0);
     -+	else
     -+		string_list_append(&reviewed_by, arg);
     -+	return 0;
     -+}
     -+
     -+static int report_callback(const struct option *opt, const char *arg, int unset)
     -+{
     -+	if (unset)
     -+		string_list_clear(&reported_by, 0);
     -+	else
     -+		string_list_append(&reported_by, arg);
     -+	return 0;
     -+}
     -+
     -+static int mentor_callback(const struct option *opt, const char *arg, int unset)
     -+{
     -+	if (unset)
     -+		string_list_clear(&mentored_by, 0);
     -+	else
     -+		string_list_append(&mentored_by, arg);
     ++	if (unset) {
     ++		strvec_clear(&run_trailer.args);
     ++		return -1;
     ++	}
     ++	run_trailer.git_cmd = 1;
     ++	strvec_pushl(&run_trailer.args, "--trailer", arg, NULL);
      +	return 0;
      +}
      +
     - int cmd_commit(int argc, const char **argv, const char *prefix)
     + static int opt_parse_porcelain(const struct option *opt, const char *arg, int unset)
       {
     - 	static struct wt_status s;
     + 	enum wt_status_format *value = (enum wt_status_format *)opt->value;
     +@@ builtin/commit.c: static int prepare_to_commit(const char *index_file, const char *prefix,
     + 
     + 	fclose(s->fp);
     + 
     ++	run_command(&run_trailer);
     ++
     + 	/*
     + 	 * Reject an attempt to record a non-merge empty commit without
     + 	 * explicit --allow-empty. In the cherry-pick case, it may be
      @@ builtin/commit.c: int cmd_commit(int argc, const char **argv, const char *prefix)
       		OPT_STRING(0, "fixup", &fixup_message, N_("commit"), N_("use autosquash formatted message to fixup 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_CALLBACK('H', "helped-by", NULL, N_("email"), N_("add a Helped-by trailer"), help_callback),
     -+		OPT_CALLBACK('r', "reported-by", NULL, N_("email"), N_("add a Reported-by trailer"), report_callback),
     -+		OPT_CALLBACK('R', "reviewed-by", NULL, N_("email"), N_("add a Reviewed-by trailer"), review_callback),
     -+		OPT_CALLBACK('M', "mentored-by", NULL, N_("email"), N_("add a Mentored-by trailer"), mentor_callback),
     ++		OPT_CALLBACK(0, "trailer", &trailer, N_("trailer"), N_("trailer(s) to add"), opt_pass_trailer),
       		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")),
      @@ builtin/commit.c: int cmd_commit(int argc, const char **argv, const char *prefix)
     - 	struct commit_extra_header *extra = NULL;
     - 	struct strbuf err = STRBUF_INIT;
     - 
     -+	helped_by.strdup_strings = 1;
     -+	reviewed_by.strdup_strings = 1;
     -+	reported_by.strdup_strings = 1;
     -+	mentored_by.strdup_strings = 1;
     -+
     - 	if (argc == 2 && !strcmp(argv[1], "-h"))
     - 		usage_with_options(builtin_commit_usage, builtin_commit_options);
     - 
     -
     - ## sequencer.c ##
     -@@ sequencer.c: int sequencer_pick_revisions(struct repository *r,
     - 	return res;
     - }
     - 
     --void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag)
     -+void append_message(struct strbuf *msgbuf, struct strbuf *sob,
     -+			size_t ignore_footer, unsigned flag)
     - {
     - 	unsigned no_dup_sob = flag & APPEND_SIGNOFF_DEDUP;
     --	struct strbuf sob = STRBUF_INIT;
     - 	int has_footer;
     - 
     --	strbuf_addstr(&sob, sign_off_header);
     --	strbuf_addstr(&sob, fmt_name(WANT_COMMITTER_IDENT));
     --	strbuf_addch(&sob, '\n');
     --
     - 	if (!ignore_footer)
     - 		strbuf_complete_line(msgbuf);
     - 
     -@@ sequencer.c: void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag)
     - 	 * If the whole message buffer is equal to the sob, pretend that we
     - 	 * found a conforming footer with a matching sob
     - 	 */
     --	if (msgbuf->len - ignore_footer == sob.len &&
     --	    !strncmp(msgbuf->buf, sob.buf, sob.len))
     -+	if (msgbuf->len - ignore_footer == sob->len &&
     -+	    !strncmp(msgbuf->buf, sob->buf, sob->len))
     - 		has_footer = 3;
     - 	else
     --		has_footer = has_conforming_footer(msgbuf, &sob, ignore_footer);
     -+		has_footer = has_conforming_footer(msgbuf, sob, ignore_footer);
     - 
     - 	if (!has_footer) {
     - 		const char *append_newlines = NULL;
     -@@ sequencer.c: void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag)
     - 
     - 	if (has_footer != 3 && (!no_dup_sob || has_footer != 2))
     - 		strbuf_splice(msgbuf, msgbuf->len - ignore_footer, 0,
     --				sob.buf, sob.len);
     -+				sob->buf, sob->len);
     -+}
     -+
     -+void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag)
     -+{
     -+	struct strbuf sob = STRBUF_INIT;
     -+	strbuf_addstr(&sob, sign_off_header);
     -+	strbuf_addstr(&sob, fmt_name(WANT_COMMITTER_IDENT));
     -+	strbuf_addch(&sob, '\n');
     -+	append_message(msgbuf, &sob, ignore_footer, flag);
     -+	strbuf_release(&sob);
     -+}
     - 
     -+void append_message_string_list(struct strbuf *msgbuf, const char *header,
     -+		struct string_list *sobs, size_t ignore_footer, unsigned flag) {
     -+	int i;
     -+	struct strbuf sob = STRBUF_INIT;
     -+
     -+	for ( i = 0; i < sobs->nr; i++)
     -+	{
     -+		strbuf_addstr(&sob, header);
     -+		strbuf_addstr(&sob, sobs->items[i].string);
     -+		strbuf_addch(&sob, '\n');
     -+		append_message(msgbuf, &sob, ignore_footer, flag);
     -+		strbuf_reset(&sob);
     -+	}
     - 	strbuf_release(&sob);
     - }
     - 
     -
     - ## sequencer.h ##
     -@@ sequencer.h: int todo_list_rearrange_squash(struct todo_list *todo_list);
     -  * and the new signoff will be spliced into the buffer before those bytes.
     -  */
     - void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
     -+void append_message(struct strbuf *msgbuf, struct strbuf *sob,
     -+		size_t ignore_footer, unsigned flag);
     -+void append_message_string_list(struct strbuf *msgbuf, const char*header,
     -+		struct string_list *sobs, size_t ignore_footer, unsigned flag);
     - 
     - void append_conflicts_hint(struct index_state *istate,
     - 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
     + 			die(_("could not parse HEAD commit"));
     + 	}
     + 	verbose = -1; /* unspecified */
     ++	strvec_pushl(&run_trailer.args, "interpret-trailers",
     ++		"--in-place", "--where=end", git_path_commit_editmsg(), NULL);
     + 	argc = parse_and_validate_options(argc, argv, builtin_commit_options,
     + 					  builtin_commit_usage,
     + 					  prefix, current_head, &s);
      
       ## t/t7502-commit-porcelain.sh ##
      @@ t/t7502-commit-porcelain.sh: test_expect_success 'sign off' '
       
       '
       
     -+test_expect_success 'helped-by' '
     -+
     ++test_expect_success 'trailer' '
      +	>file1 &&
      +	git add file1 &&
     -+	git commit --helped-by="foo <bar@frotz>" \
     -+	--helped-by="foo2 <bar2@frotz>" -m "thank you" &&
     -+	git cat-file commit HEAD >commit.msg &&
     -+	sed -ne "s/Helped-by: //p" commit.msg >actual &&
     -+	cat >expected <<-\EOF &&
     -+	foo <bar@frotz>
     -+	foo2 <bar2@frotz>
     -+	EOF
     -+	test_cmp expected actual
     -+
     -+'
     -+
     -+test_expect_success 'reported-by' '
     -+
     -+	>file2 &&
     -+	git add file2 &&
     -+	git commit --reported-by="foo <bar@frotz>" \
     -+	--reported-by="foo2 <bar2@frotz>" -m "thank you" &&
     -+	git cat-file commit HEAD >commit.msg &&
     -+	sed -ne "s/Reported-by: //p" commit.msg >actual &&
     -+	cat >expected <<-\EOF &&
     -+	foo <bar@frotz>
     -+	foo2 <bar2@frotz>
     -+	EOF
     -+	test_cmp expected actual
     -+
     -+'
     -+
     -+test_expect_success 'reviewed-by' '
     -+
     -+	>file3 &&
     -+	git add file3 &&
     -+	git commit --reviewed-by="foo <bar@frotz>" \
     -+	--reviewed-by="foo2 <bar2@frotz>" -m "thank you" &&
     -+	git cat-file commit HEAD >commit.msg &&
     -+	sed -ne "s/Reviewed-by: //p" commit.msg >actual &&
     -+	cat >expected <<-\EOF &&
     -+	foo <bar@frotz>
     -+	foo2 <bar2@frotz>
     -+	EOF
     -+	test_cmp expected actual
     -+
     -+'
     -+
     -+test_expect_success 'mentored-by' '
     -+
     -+	>file4 &&
     -+	git add file4 &&
     -+	git commit --mentored-by="foo <bar@frotz>" \
     -+	--mentored-by="foo2 <bar2@frotz>" -m "thank you" &&
     -+	git cat-file commit HEAD >commit.msg &&
     -+	sed -ne "s/Mentored-by: //p" commit.msg >actual &&
     -+	cat >expected <<-\EOF &&
     -+	foo <bar@frotz>
     -+	foo2 <bar2@frotz>
     -+	EOF
     -+	test_cmp expected actual
     -+
     -+'
     -+
     -+test_expect_success 'multiple signatures' '
     -+
     -+	>file5 &&
     -+	git add file5 &&
     -+	git commit --helped-by="foo <bar@frotz>" \
     -+	--reviewed-by="foo2 <bar2@frotz>" \
     -+	--mentored-by="foo3 <bar3@frotz>" \
     -+	--reported-by="foo4 <bar4@frotz>" -s -m "thank you" &&
     ++	git commit -s --trailer "Signed-off-by:C O Mitter1 [off-list ref]" \
     ++	--trailer "Helped-by:C O Mitter2 [off-list ref]"  \
     ++	--trailer "Reported-by:C O Mitter3 [off-list ref]" \
     ++	--trailer "Mentored-by:C O Mitter4 [off-list ref]" \
     ++	-m "hello" &&
      +	git cat-file commit HEAD >commit.msg &&
      +	sed -e "1,7d" commit.msg >actual &&
      +	cat >expected <<-\EOF &&
      +	Signed-off-by: C O Mitter [off-list ref]
     -+	Helped-by: foo <bar@frotz>
     -+	Reviewed-by: foo2 <bar2@frotz>
     -+	Reported-by: foo4 <bar4@frotz>
     -+	Mentored-by: foo3 <bar3@frotz>
     ++	Signed-off-by: C O Mitter1 [off-list ref]
     ++	Helped-by: C O Mitter2 [off-list ref]
     ++	Reported-by: C O Mitter3 [off-list ref]
     ++	Mentored-by: C O Mitter4 [off-list ref]
      +	EOF
      +	test_cmp expected actual
     -+
     -+'
     -+
     -+test_expect_success 'multiple signatures (use abbreviations)' '
     -+
     -+	>file6 &&
     -+	git add file6 &&
     -+	git commit -H "foo <bar@frotz>" \
     -+	-R "foo2 <bar2@frotz>" \
     -+	-M "foo3 <bar3@frotz>" \
     -+	-r "foo4 <bar4@frotz>" -s -m "thank you" &&
     -+	git cat-file commit HEAD >commit.msg &&
     -+	sed -e "1,7d" commit.msg >actual &&
     -+	cat >expected <<-\EOF &&
     -+	Signed-off-by: C O Mitter [off-list ref]
     -+	Helped-by: foo <bar@frotz>
     -+	Reviewed-by: foo2 <bar2@frotz>
     -+	Reported-by: foo4 <bar4@frotz>
     -+	Mentored-by: foo3 <bar3@frotz>
     -+	EOF
     -+	test_cmp expected actual
     -+
      +'
      +
       test_expect_success 'multiple -m' '


 Documentation/git-commit.txt |  8 +++++++-
 builtin/commit.c             | 18 ++++++++++++++++++
 t/t7502-commit-porcelain.sh  | 20 ++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index 17150fa7eabe..764513a3f287 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt

@@ -14,7 +14,7 @@ SYNOPSIS
 	   [--allow-empty-message] [--no-verify] [-e] [--author=<author>]
 	   [--date=<date>] [--cleanup=<mode>] [--[no-]status]
 	   [-i | -o] [--pathspec-from-file=<file> [--pathspec-file-nul]]
-	   [-S[<keyid>]] [--] [<pathspec>...]
+	   [-S[<keyid>]] [--] [<pathspec>...] [(--trailer <token>[(=|:)<value>])...]
 
 DESCRIPTION
 -----------

@@ -166,6 +166,12 @@ The `-m` option is mutually exclusive with `-c`, `-C`, and `-F`.
 
 include::signoff-option.txt[]
 
+--trailer <token>[(=|:)<value>]::
+	Specify a (<token>, <value>) pair that should be applied as a
+	trailer. (e.g.  `git commit --trailer "Signed-off-by:C O Mitter <committer@example.com>" \
+	--trailer "Helped-by:C O Mitter <committer@example.com>"`will add the "Signed-off" trailer
+	and the "Helped-by" trailer in the commit message.)
+
 -n::
 --no-verify::
 	This option bypasses the pre-commit and commit-msg hooks.

diff --git a/builtin/commit.c b/builtin/commit.c
index 739110c5a7f6..abbd136b27f0 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c

@@ -113,6 +113,8 @@ static int config_commit_verbose = -1; /* unspecified */
 static int no_post_rewrite, allow_empty_message, pathspec_file_nul;
 static char *untracked_files_arg, *force_date, *ignore_submodule_arg, *ignored_arg;
 static char *sign_commit, *pathspec_from_file;
+struct child_process run_trailer = CHILD_PROCESS_INIT;
+static const char *trailer;
 
 /*
  * The default commit message cleanup mode will remove the lines

@@ -131,6 +133,17 @@ static struct strbuf message = STRBUF_INIT;
 
 static enum wt_status_format status_format = STATUS_FORMAT_UNSPECIFIED;
 
+static int opt_pass_trailer(const struct option *opt, const char *arg, int unset)
+{
+	if (unset) {
+		strvec_clear(&run_trailer.args);
+		return -1;
+	}
+	run_trailer.git_cmd = 1;
+	strvec_pushl(&run_trailer.args, "--trailer", arg, NULL);
+	return 0;
+}
+
 static int opt_parse_porcelain(const struct option *opt, const char *arg, int unset)
 {
 	enum wt_status_format *value = (enum wt_status_format *)opt->value;

@@ -958,6 +971,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 
 	fclose(s->fp);
 
+	run_command(&run_trailer);
+
 	/*
 	 * Reject an attempt to record a non-merge empty commit without
 	 * explicit --allow-empty. In the cherry-pick case, it may be

@@ -1507,6 +1522,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "fixup", &fixup_message, N_("commit"), N_("use autosquash formatted message to fixup 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_CALLBACK(0, "trailer", &trailer, N_("trailer"), N_("trailer(s) to add"), opt_pass_trailer),
 		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")),

@@ -1577,6 +1593,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 			die(_("could not parse HEAD commit"));
 	}
 	verbose = -1; /* unspecified */
+	strvec_pushl(&run_trailer.args, "interpret-trailers",
+		"--in-place", "--where=end", git_path_commit_editmsg(), NULL);
 	argc = parse_and_validate_options(argc, argv, builtin_commit_options,
 					  builtin_commit_usage,
 					  prefix, current_head, &s);

diff --git a/t/t7502-commit-porcelain.sh b/t/t7502-commit-porcelain.sh
index 6396897cc818..4b9ac4587d17 100755
--- a/t/t7502-commit-porcelain.sh
+++ b/t/t7502-commit-porcelain.sh

@@ -154,6 +154,26 @@ test_expect_success 'sign off' '
 
 '
 
+test_expect_success 'trailer' '
+	>file1 &&
+	git add file1 &&
+	git commit -s --trailer "Signed-off-by:C O Mitter1 <committer1@example.com>" \
+	--trailer "Helped-by:C O Mitter2 <committer2@example.com>"  \
+	--trailer "Reported-by:C O Mitter3 <committer3@example.com>" \
+	--trailer "Mentored-by:C O Mitter4 <committer4@example.com>" \
+	-m "hello" &&
+	git cat-file commit HEAD >commit.msg &&
+	sed -e "1,7d" commit.msg >actual &&
+	cat >expected <<-\EOF &&
+	Signed-off-by: C O Mitter <committer@example.com>
+	Signed-off-by: C O Mitter1 <committer1@example.com>
+	Helped-by: C O Mitter2 <committer2@example.com>
+	Reported-by: C O Mitter3 <committer3@example.com>
+	Mentored-by: C O Mitter4 <committer4@example.com>
+	EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'multiple -m' '
 
 	>negative &&

base-commit: 13d7ab6b5d7929825b626f050b62a11241ea4945
-- 
gitgitgadget