[PATCH v5 0/7] cherry-pick: add `--empty` for more robust redundant commit handling

The ultimate goal of this series is to allow git-cherry-pick(1) to automatically drop redundant commits. The mechanism chosen is an `--empty` option that provides the same flexibility as the `--empty` options for git-rebase(1) and git-am(1).

Some secondary goals are to improve the consistency in the values and documentation for this option across the three commands.

See "Does extending `--empty` to git-cherry-pick make sense?" [1] for some context for why this option is desired in git-cherry-pick(1).

[1]: https://lore.kernel.org/git/CAHPHrSevBdQF0BisR8VK=jM=wj1dTUYEVrv31gLerAzL9=Cd8Q@mail.gmail.com

Along the way, I (with some help from Elijah and Phillip) found a few other things in the docs and related sequencer code to clean up.

This is the final planned re-roll of this series, addressing two minor style concerns with commit 4/7 as noted in this [2] thread. All other commits are left unchanged.

[2]: https://lore.kernel.org/git/xmqqa5mmhvx5.fsf@gitster.g

Range-diff from v4:

1:  f6b8a655cd = 1:  f6b8a655cd docs: address inaccurate `--empty` default with `--exec`
2:  401de76c0b = 2:  401de76c0b docs: clean up `--empty` formatting in git-rebase(1) and git-am(1)
3:  031b3bb7bb = 3:  031b3bb7bb rebase: update `--empty=ask` to `--empty=stop`
4:  fd53c39482 ! 4:  d3bfe41819 sequencer: handle unborn branch with `--allow-empty`
    @@ sequencer.c: static struct object_id *get_cache_tree_oid(struct index_state *ist
      	struct commit *head_commit;
      	struct index_state *istate = r->index;
     +	const char *head_name;
    -
    --	if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
    --		return error(_("could not resolve HEAD commit"));
    ++
     +	if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL)) {
    -+		/*
    -+		 * Check to see if this is an unborn branch
    -+		 */
    -+		head_name = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE, &head_oid, NULL);
    -+		if (!head_name || !starts_with(head_name, "refs/heads/") || !is_null_oid(&head_oid))
    ++		/* Check to see if this is an unborn branch */
    ++		head_name = resolve_ref_unsafe("HEAD",
    ++			RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
    ++			&head_oid, NULL);
    ++		if (!head_name ||
    ++			!starts_with(head_name, "refs/heads/") ||
    ++			!is_null_oid(&head_oid))
     +			return error(_("could not resolve HEAD commit"));
     +		head_tree_oid = the_hash_algo->empty_tree;
     +	} else {
     +		head_commit = lookup_commit(r, &head_oid);

    +-	if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
    +-		return error(_("could not resolve HEAD commit"));
    +-
     -	head_commit = lookup_commit(r, &head_oid);
     +		/*
     +		 * If head_commit is NULL, check_commit, called from
5:  90dca45c12 = 5:  5e690bca6e sequencer: do not require `allow_empty` for redundant commit options
6:  ab3b6afc97 = 6:  ed03908e9e cherry-pick: enforce `--keep-redundant-commits` incompatibility
7:  0e2577ea56 = 7:  d3cf068c45 cherry-pick: add `--empty` for more robust redundant commit handling

Brian Lyles (7):
  docs: address inaccurate `--empty` default with `--exec`
  docs: clean up `--empty` formatting in git-rebase(1) and git-am(1)
  rebase: update `--empty=ask` to `--empty=stop`
  sequencer: handle unborn branch with `--allow-empty`
  sequencer: do not require `allow_empty` for redundant commit options
  cherry-pick: enforce `--keep-redundant-commits` incompatibility
  cherry-pick: add `--empty` for more robust redundant commit handling

 Documentation/git-am.txt          | 20 ++++++---
 Documentation/git-cherry-pick.txt | 30 ++++++++++---
 Documentation/git-rebase.txt      | 26 +++++++----
 builtin/rebase.c                  | 16 ++++---
 builtin/revert.c                  | 38 +++++++++++++++-
 sequencer.c                       | 72 ++++++++++++++++++-------------
 t/t3424-rebase-empty.sh           | 55 +++++++++++++++++++++--
 t/t3501-revert-cherry-pick.sh     | 14 ++++--
 t/t3505-cherry-pick-empty.sh      | 51 +++++++++++++++++++++-
 t/t3510-cherry-pick-sequence.sh   | 32 ++++++++++++++
 10 files changed, 286 insertions(+), 68 deletions(-)