[PATCH v6 0/6][Outreachy] commit: Implementation of "amend!" commit

[Charvi Mendiratta <charvi077@gmail.com>]

This patch series teaches `git commit --fixup` to create "amend!" commit
as an alternative that works with `git rebase --autosquash`. It allows to
fixup both the content and the commit message of the specified commit.
Here we add two suboptions to the `--fixup`, first `amend` suboption that
creates an "amend!" commit. It takes the staged changes and also allows to
edit the commit message of the commit we are fixing.
Example usuage:
git commit --fixup=amend:<commit>

Secondly, `reword` suboption that creates an empty "amend!" commit i.e it
ignores the staged changes and only allows to reword/edit the commit message
of the commit we are fixing. `--fixup=reword:<commit>` is a short-hand of
`--fixup=amend:<commit> --only`.
Example usuage:
git commit --fixup=reword:<commit>

** This work is rebased on the top of cm/rebase-i-updates.

Charvi Mendiratta (6):
  sequencer: export and rename subject_length()
  commit: add amend suboption to --fixup to create amend! commit
  commit: add a reword suboption to --fixup
  t7500: add tests for --fixup=[amend|reword] options
  t3437: use --fixup with options to create amend! commit
  doc/git-commit: add documentation for fixup=[amend|reword] options

 Documentation/git-commit.txt              |  45 +++++-
 Documentation/git-rebase.txt              |  21 +--
 builtin/commit.c                          | 122 +++++++++++++++--
 commit.c                                  |  14 ++
 commit.h                                  |   3 +
 sequencer.c                               |  16 +--
 t/t3437-rebase-fixup-options.sh           |  30 +---
 t/t7500-commit-template-squash-signoff.sh | 159 ++++++++++++++++++++++
 8 files changed, 342 insertions(+), 68 deletions(-)

Range-diff against v5:
-:  ---------- > 1:  a2e89540ec sequencer: export and rename subject_length()
1:  be2808a255 ! 2:  f3cdb3eb1e commit: add amend suboption to --fixup to create amend! commit
    @@ builtin/commit.c: static int prepare_to_commit(const char *index_file, const cha
      	} else if (!stat(git_path_merge_msg(the_repository), &statbuf)) {
      		size_t merge_msg_start;

    -@@ builtin/commit.c: static void finalize_deferred_config(struct wt_status *s)
    - 		s->ahead_behind_flags = AHEAD_BEHIND_FULL;
    - }
    -
    -+/* returns the length of intial segment of alpha characters only */
    -+static size_t skip_suboption(char *fixup_message) {
    -+	const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
    -+	return strspn(fixup_message, alphas);
    -+}
    -+
    - static int parse_and_validate_options(int argc, const char *argv[],
    - 				      const struct option *options,
    - 				      const char * const usage[],
     @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *argv[],
      	if (force_author && renew_authorship)
      		die(_("Using both --reset-author and --author does not make sense"));
    @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *ar
     +		 *
     +		 * Otherwise, we are dealing with --fixup=<commit>.
     +		 */
    -+		size_t len = skip_suboption(fixup_message);
    -+		if (len && fixup_message[len] == ':') {
    -+			fixup_message[len++] = '\0';
    -+			fixup_commit = fixup_message + len;
    ++		char *p = fixup_message;
    ++		while (isalpha(*p))
    ++			p++;
    ++		if (p > fixup_message && *p == ':') {
    ++			*p = '\0';
    ++			fixup_commit = p + 1;
     +			if (!strcmp("amend", fixup_message)) {
     +				fixup_prefix = "amend";
     +				allow_empty = 1;
2:  f6217338c1 ! 3:  ded339706f commit: add a reword suboption to --fixup
    @@ builtin/commit.c: static void finalize_deferred_config(struct wt_status *s)
     +		die(_("reword option of --fixup is mutually exclusive with --patch/--interactive/--all/--include/--only"));
     +}
     +
    - /* returns the length of intial segment of alpha characters only */
    - static size_t skip_suboption(char *fixup_message) {
    - 	const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
    + static int parse_and_validate_options(int argc, const char *argv[],
    + 				      const struct option *options,
    + 				      const char * const usage[],
     @@ builtin/commit.c: 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,
    @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *ar
      		 * Otherwise, we are dealing with --fixup=<commit>.
      		 */
     @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *argv[],
    - 		if (len && fixup_message[len] == ':') {
    - 			fixup_message[len++] = '\0';
    - 			fixup_commit = fixup_message + len;
    + 		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)) {
3:  1a127dc0b3 = 4:  ec6f3d5d7d t7500: add tests for --fixup=[amend|reword] options
4:  be6f4fa0d1 = 5:  148087b133 t3437: use --fixup with options to create amend! commit
5:  79c098df2c ! 6:  2b750d305e doc/git-commit: add documentation for fixup=[amend|reword] options
    @@ Commit message

         Mentored-by: Christian Couder <chriscool@tuxfamily.org>
         Mentored-by: Phillip Wood <phillip.wood@dunelm.org.uk>
    +    Helped-by: Eric Sunshine <sunshine@sunshineco.com>
         Helped-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
         Signed-off-by: Charvi Mendiratta <charvi077@gmail.com>
--
2.29.0.rc1