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

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

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".

> 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;