[RFC PATCH] `log --merge` also for rebase/cherry pick/revert

[Michael Lohmann <mi.al.lohmann@gmail.com>]

This extends the functionality of `git log --merge` to also work with
conflicts for rebase, cherry pick and revert.

Signed-off-by: Michael Lohmann <mi.al.lohmann@gmail.com>
---
Hi everybody!

When Phillip Wood gave me some nice hints on his workflow concerning
conflicts [1] (we discussed if `--show-current-patch` would make sense
for cherry pick/revert). When I learned about `git log --merge` I was a
bit sad to discover that those do not exist for rebase/revert/cherry
pick since they look really valuable for getting an understanding on
what was changed. It is basically the counterpart to
`git show ${ACTION}_HEAD` for understanding the source of the conflict.

I am curious if also other people would be interested in having an easy
way to get a log of only the relevant commits touching conflicting files
for said actions.

With this patch I think the functionality is there, just hijacking the
`--merge` code - maybe an alias like `git log --conflict` or similar
might be more descriptive now?

What do you think about this idea? (Or am I maybe missing an easy way to
achieve it with the existing code as well?)

Michael


[1] https://lore.kernel.org/git/cfba7098-3c23-4a81-933c-b7fefdedec8a@gmail.com/

 revision.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/revision.c b/revision.c
index 2424c9bd67..2e5c00dabd 100644
--- a/revision.c
+++ b/revision.c
@@ -1961,23 +1961,37 @@ static void add_pending_commit_list(struct rev_info *revs,
 	}
 }
 
+static char* get_action_head_name(struct object_id* oid)
+{
+	if (!repo_get_oid(the_repository, "MERGE_HEAD", oid)) {
+		return "MERGE_HEAD";
+	} else if (!repo_get_oid(the_repository, "REBASE_HEAD", oid)) {
+		return "REBASE_HEAD";
+	} else if (!repo_get_oid(the_repository, "CHERRY_PICK_HEAD", oid)) {
+		return "CHERRY_PICK_HEAD";
+	} else if (!repo_get_oid(the_repository, "REVERT_HEAD", oid)) {
+		return "REVERT_HEAD";
+	} else
+		die("--merge without MERGE_HEAD, REBASE_HEAD, CHERRY_PICK_HEAD or REVERT_HEAD?");
+}
+
 static void prepare_show_merge(struct rev_info *revs)
 {
 	struct commit_list *bases;
 	struct commit *head, *other;
 	struct object_id oid;
 	const char **prune = NULL;
+	const char *action_head_name;
 	int i, prune_num = 1; /* counting terminating NULL */
 	struct index_state *istate = revs->repo->index;
 
 	if (repo_get_oid(the_repository, "HEAD", &oid))
 		die("--merge without HEAD?");
 	head = lookup_commit_or_die(&oid, "HEAD");
-	if (repo_get_oid(the_repository, "MERGE_HEAD", &oid))
-		die("--merge without MERGE_HEAD?");
-	other = lookup_commit_or_die(&oid, "MERGE_HEAD");
+	action_head_name = get_action_head_name(&oid);
+	other = lookup_commit_or_die(&oid, action_head_name);
 	add_pending_object(revs, &head->object, "HEAD");
-	add_pending_object(revs, &other->object, "MERGE_HEAD");
+	add_pending_object(revs, &other->object, action_head_name);
 	bases = repo_get_merge_bases(the_repository, head, other);
 	add_rev_cmdline_list(revs, bases, REV_CMD_MERGE_BASE, UNINTERESTING | BOTTOM);
 	add_pending_commit_list(revs, bases, UNINTERESTING | BOTTOM);
-- 
2.39.3 (Apple Git-145)