commit: add a reword suboption to --fixup

`git commit --fixup=reword:<commit>` aliases
`--fixup=amend:<commit> --only`, where it creates an empty "amend!"
commit that will reword <commit> without changing its contents when
it is rebased with `--autosquash`.

Mentored-by: Christian Couder <[email protected]>
Mentored-by: Phillip Wood <[email protected]>
Helped-by: Junio C Hamano <[email protected]>
Helped-by: Eric Sunshine <[email protected]>
Signed-off-by: Charvi Mendiratta <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: charvi-077

builtin/commit.c

@@ -1188,6 +1188,19 @@ static void finalize_deferred_config(struct wt_status *s)
 		s->ahead_behind_flags = AHEAD_BEHIND_FULL;
 }
 
+static void check_fixup_reword_options(int argc, const char *argv[]) {
+	if (whence != FROM_COMMIT) {
+		if (whence == FROM_MERGE)
+			die(_("You are in the middle of a merge -- cannot reword."));
+		else if (is_from_cherry_pick(whence))
+			die(_("You are in the middle of a cherry-pick -- cannot reword."));
+	}
+	if (argc)
+		die(_("cannot combine reword option of --fixup with path '%s'"), *argv);
+	if (patch_interactive || interactive || all || also || only)
+		die(_("reword option of --fixup is mutually exclusive with --patch/--interactive/--all/--include/--only"));
+}
+
 static int parse_and_validate_options(int argc, const char *argv[],
 				      const struct option *options,
 				      const char * const usage[],
@@ -1269,8 +1282,9 @@ static int parse_and_validate_options(int argc, const char *argv[],
 		 * We limit --fixup's suboptions to only alpha characters.
 		 * If the first character after a run of alpha is colon,
 		 * then the part before the colon may be a known suboption
-		 * name `amend` or a misspelt suboption name. In this case,
-		 * we treat it as --fixup=<suboption>:<arg>.
+		 * name like `amend` or `reword`, or a misspelt suboption
+		 * name. In either case, we treat it as
+		 * --fixup=<suboption>:<arg>.
 		 *
 		 * Otherwise, we are dealing with --fixup=<commit>.
 		 */
@@ -1280,9 +1294,14 @@ static int parse_and_validate_options(int argc, const char *argv[],
 		if (p > fixup_message && *p == ':') {
 			*p = '\0';
 			fixup_commit = p + 1;
-			if (!strcmp("amend", fixup_message)) {
+			if (!strcmp("amend", fixup_message) ||
+			    !strcmp("reword", fixup_message)) {
 				fixup_prefix = "amend";
 				allow_empty = 1;
+				if (*fixup_message == 'r') {
+					check_fixup_reword_options(argc, argv);
+					only = 1;
+				}
 			} else {
 				die(_("unknown option: --fixup=%s:%s"), fixup_message, fixup_commit);
 			}
@@ -1571,10 +1590,10 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		OPT_STRING('c', "reedit-message", &edit_message, N_("commit"), N_("reuse and edit message from specified commit")),
 		OPT_STRING('C', "reuse-message", &use_message, N_("commit"), N_("reuse message from specified commit")),
 		/*
-		 * TRANSLATORS: Leave "[amend:]" as-is, and
-		 * only translate <commit>.
+		 * TRANSLATORS: Leave "[(amend|reword):]" as-is,
+		 * and only translate <commit>.
 		 */
-		OPT_STRING(0, "fixup", &fixup_message, N_("[amend:]commit"), N_("use autosquash formatted message to fixup or amend specified commit")),
+		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_BOOL('s', "signoff", &signoff, N_("add a Signed-off-by trailer")),