[PATCH v6] [GSOC] commit: add --trailer option

@@ -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 +166,13 @@ 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.

@@ -113,6 +113,7 @@ 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 strvec trailer_args = STRVEC_INIT;
 
 /*
  * The default commit message cleanup mode will remove the lines

@@ -131,6 +132,14 @@ 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)
+{
+	BUG_ON_OPT_NEG(unset);
+
+	strvec_pushl(&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 +967,18 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 
 	fclose(s->fp);
 
+	if (trailer_args.nr) {
+		static struct child_process run_trailer = CHILD_PROCESS_INIT;
+
+		strvec_pushl(&run_trailer.args, "interpret-trailers",
+			     "--in-place", "--where=end", git_path_commit_editmsg(), NULL);
+		strvec_pushv(&run_trailer.args, trailer_args.v);
+		run_trailer.git_cmd = 1;
+		if (run_command(&run_trailer))
+			strvec_clear(&run_trailer.args);
+		strvec_clear(&trailer_args);
+	}
+
 	/*
 	 * Reject an attempt to record a non-merge empty commit without
 	 * explicit --allow-empty. In the cherry-pick case, it may be

@@ -1507,6 +1528,7 @@ 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_F(0, "trailer", NULL, N_("trailer"), N_("trailer(s) to add"), PARSE_OPT_NONEG, 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")),

@@ -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 &&