[PATCH 2/2] sequencer: don't say BUG on bogus input

[Jeff King <peff@peff.net>]

When cherry-picking a single commit, we go through a special
code path that avoids creating a sequencer todo list at all.
This path expects our revision parsing to turn up exactly
one commit, and dies with a BUG if it doesn't.

But it's actually quite easy to fool. For example:

  $ git cherry-pick --author=no.such.person HEAD
  error: BUG: expected exactly one commit from walk
  fatal: cherry-pick failed

This isn't a bug; it's just bogus input.

Let's drop the "BUG" to make it clear that the input is the
problem. And let's also use the phrase "empty commit set
passed", which matches what we say when we do a real
revision walk and it turns up empty.

This BUG dates back to 7acaaac275 (revert: allow single-pick
in the middle of cherry-pick sequence, 2011-12-10), and
could be triggered in the same way even then. So clearly
this outcome is unexpected. Another approach would be to
make the conditional from 7acaaac275 smarter, and avoid even
entering this single-pick case.  But since the action is
identical either way (we have nothing to pick, so we exit)
there's not much point in trying to distinguish the two.

Signed-off-by: Jeff King <peff@peff.net>
---
 sequencer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sequencer.c b/sequencer.c
index f692b2ef44..234666b980 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3637,7 +3637,7 @@ int sequencer_pick_revisions(struct replay_opts *opts)
 			return error(_("revision walk setup failed"));
 		cmit = get_revision(opts->revs);
 		if (!cmit || get_revision(opts->revs))
-			return error("BUG: expected exactly one commit from walk");
+			return error(_("empty commit set passed"));
 		return single_pick(cmit, opts);
 	}
 
-- 
2.18.0.400.g702e398724