[PATCH v6 0/2] Implement `git log --merge` also for rebase/cherry-pick/revert

Changes in v6:
- Changed the error message added in 1/2 and adjusted in 2/2 to avoid a rhetorical
question

Changes in v5:
- Marked error messages for translation and tweaked them as suggested by Phillip
- Reworded the message of 2/2 as suggested by Phillip
- Removed the change to gitk's doc in 2/2 as pointed out by Johannes
- Fixed the trailers in 2/2
- Improved the doc in 2/2 as suggested by Phillip and Jean-Noël

Changes in v4:
- Added a commit message for 2/2 detailing the use case and summarizing the discussion in the thread
- Adjusted the documentation of the option

---
Michael Lohmann (2):
      revision: ensure MERGE_HEAD is a ref in prepare_show_merge
      revision: implement `git log --merge` also for rebase/cherry-pick/revert

 Documentation/rev-list-options.txt |  7 +++++--
 revision.c                         | 27 +++++++++++++++++++++++----
 2 files changed, 28 insertions(+), 6 deletions(-)
---
base-commit: 3c2a3fdc388747b9eaf4a4a4f2035c1c9ddb26d0
change-id: 20240210-ml-log-merge-with-cherry-pick-and-other-pseudo-heads-05bd8e8797db

Range-diff versus v5:

1:  c9536431d1 ! 1:  363657561c revision: ensure MERGE_HEAD is a ref in prepare_show_merge
    @@ Commit message
         (2) obtain the oid without any prefixing by refs.c:repo_dwim_ref()
         (3) error out when MERGE_HEAD is a symref.
     
    +    Note that we avoid marking the new error message for translation as it
    +    will be done in the next commit when the message is generalized to other
    +    special refs.
    +
         Helped-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Michael Lohmann <mi.al.lohmann@gmail.com>
         Signed-off-by: Junio C Hamano <gitster@pobox.com>
    @@ revision.c: static void prepare_show_merge(struct rev_info *revs)
     +			&oid, NULL))
      		die("--merge without MERGE_HEAD?");
     +	if (is_null_oid(&oid))
    -+		die(_("MERGE_HEAD is a symbolic ref?"));
    ++		die(_("MERGE_HEAD exists but is a symbolic ref"));
      	other = lookup_commit_or_die(&oid, "MERGE_HEAD");
      	add_pending_object(revs, &head->object, "HEAD");
      	add_pending_object(revs, &other->object, "MERGE_HEAD");
2:  1641c4be81 ! 2:  749abadc04 revision: implement `git log --merge` also for rebase/cherry-pick/revert
    @@ revision.c: static void add_pending_commit_list(struct rev_info *revs,
     +				RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
     +				oid, NULL)) {
     +			if (is_null_oid(oid))
    -+				die(_("%s is a symbolic ref?"), other_head[i]);
    ++				die(_("%s exists but is a symbolic ref"), other_head[i]);
     +			return other_head[i];
     +		}
     +
    @@ revision.c: static void prepare_show_merge(struct rev_info *revs)
     -			&oid, NULL))
     -		die("--merge without MERGE_HEAD?");
     -	if (is_null_oid(&oid))
    --		die(_("MERGE_HEAD is a symbolic ref?"));
    +-		die(_("MERGE_HEAD exists but is a symbolic ref"));
     -	other = lookup_commit_or_die(&oid, "MERGE_HEAD");
     +	other_name = lookup_other_head(&oid);
     +	other = lookup_commit_or_die(&oid, other_name);