cherry-pick: add `--empty` for more robust redundant commit handling

As with git-rebase(1) and git-am(1), git-cherry-pick(1) can result in a
commit being made redundant if the content from the picked commit is
already present in the target history. However, git-cherry-pick(1) does
not have the same options available that git-rebase(1) and git-am(1) have.

There are three things that can be done with these redundant commits:
drop them, keep them, or have the cherry-pick stop and wait for the user
to take an action. git-rebase(1) has the `--empty` option added in commit
e98c4269c8 (rebase (interactive-backend): fix handling of commits that
become empty, 2020-02-15), which handles all three of these scenarios.
Similarly, git-am(1) got its own `--empty` in 7c096b8d61 (am: support
--empty=<option> to handle empty patches, 2021-12-09).

git-cherry-pick(1), on the other hand, only supports two of the three
possiblities: Keep the redundant commits via `--keep-redundant-commits`,
or have the cherry-pick fail by not specifying that option. There is no
way to automatically drop redundant commits.

In order to bring git-cherry-pick(1) more in-line with git-rebase(1) and
git-am(1), this commit adds an `--empty` option to git-cherry-pick(1). It
has the same three options (keep, drop, and stop), and largely behaves
the same. The notable difference is that for git-cherry-pick(1), the
default will be `stop`, which maintains the current behavior when the
option is not specified.

Like the existing `--keep-redundant-commits`, `--empty=keep` will imply
`--allow-empty`.

The `--keep-redundant-commits` option will be documented as a deprecated
synonym of `--empty=keep`, and will be supported for backwards
compatibility for the time being.

Signed-off-by: Brian Lyles <brianmlyles@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/sequencer.c b/sequencer.c
index 1964977545..879b8ba2c0 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2932,6 +2932,9 @@ static int populate_opts_cb(const char *key, const char *value,
 	else if (!strcmp(key, "options.allow-empty-message"))
 		opts->allow_empty_message =
 			git_config_bool_or_int(key, value, ctx->kvi, &error_flag);
+	else if (!strcmp(key, "options.drop-redundant-commits"))
+		opts->drop_redundant_commits =
+			git_config_bool_or_int(key, value, ctx->kvi, &error_flag);
 	else if (!strcmp(key, "options.keep-redundant-commits"))
 		opts->keep_redundant_commits =
 			git_config_bool_or_int(key, value, ctx->kvi, &error_flag);
@@ -3476,6 +3479,9 @@ static int save_opts(struct replay_opts *opts)
 	if (opts->allow_empty_message)
 		res |= git_config_set_in_file_gently(opts_file,
 				"options.allow-empty-message", "true");
+	if (opts->drop_redundant_commits)
+		res |= git_config_set_in_file_gently(opts_file,
+				"options.drop-redundant-commits", "true");
 	if (opts->keep_redundant_commits)
 		res |= git_config_set_in_file_gently(opts_file,
 				"options.keep-redundant-commits", "true");