Re: [BUG] git cherry-pick does not complain about unknown options

From: Jeff King <peff@peff.net>
Date: Jul 9, 2018, 19:16 UTC
Message-ID: <20180709191607.GA9852@sigill.intra.peff.net>
In-Reply-To: <33d3e45b-1245-9e2f-42ea-a654a593bf10@gmail.com>

On Mon, Jul 09, 2018 at 04:16:16PM +0200, Andrei Rybak wrote:

> I was trying to cherry pick commits, while simultaneously changing the
> author.  Unfortunately, cherry-pick doesn't have the same --author
> option as git-commit.  However, instead of complaining about unknown
> option:

Yeah, its "--author" option is interpreted by revision.c similar to "log --author" (because we just pass all unknown options to the traversal machinery). So you could say:

  git cherry-pick --author=peff v1.0..v2.0

to pick all of my commits between the two versions. I'm not sure if that would ever be _useful_, but that's how it has behaved since 7e2bfd3f99 (revert: allow cherry-picking more than one commit, 2010-06-02), I think.

I agree that having something similar to commit's "--author" (or even just "--reset-author") would be useful. When I've had to do this before, I usually just cherry-pick and then follow-up with "commit --amend --author" (or use "rebase -i" if there are several commits). You can also do "cherry-pick -n $commit" followed by "commit -c $commit".

Show 7 quoted lines

> All commits in tests existed in repository:
> 
>     $ git cherry-pick --author='TEST' <one-commit> # case 1
>     error: BUG: expected exactly one commit from walk
>     fatal: cherry-pick failed
>     $ echo $?
>     128

I think it's reasonable for this to issue an error. But a BUG is definitely wrong. The error is more like "empty commit set passed", which is what we get for something like:

  $ git cherry-pick HEAD..HEAD
  error: empty commit set passed
  fatal: cherry-pick failed

that triggers the revision walker but has no positive commits. But we don't trigger that code because the single-rev case has some magic to allow a cherry-pick during another sequencer operation.

So I think that BUG message needs to be softened.

>     $ git cherry-pick --author='TEST' <commit1> <commit2>  # case 2
>     $ echo $?
>     0

And here we come up with an empty set, but we don't flag it as an error at all. I could even accept that philosophically as "empty input, nothing to do", but we clearly do flag it as an error in the case I showed above.

I think the problem is that we catch the error in sequencer.c:prepare_revs(), after prepare_revision_walk() returns no commits. But we _do_ have a starting commit for this case, and it's not culled until we actually ask get_revisions() to start walking.

I think we'd want something like this:

diff --git a/sequencer.c b/sequencer.c
index 4034c0461b..b978157399 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1860,8 +1860,6 @@ static int prepare_revs(struct replay_opts *opts)
 	if (prepare_revision_walk(opts->revs))
 		return error(_("revision walk setup failed"));
 
-	if (!opts->revs->commits)
-		return error(_("empty commit set passed"));
 	return 0;
 }
 
@@ -2314,6 +2312,10 @@ static int walk_revs_populate_todo(struct todo_list *todo_list,
 			short_commit_name(commit), subject_len, subject);
 		unuse_commit_buffer(commit, commit_buffer);
 	}
+
+	if (!todo_list->nr)
+		return error(_("empty commit set passed"));
+
 	return 0;
 }
 

-Peff