[PATCH 3/3] lei_to_mail: show supported mbox formats on error

[Eric Wong <e@80x24.org>]

Users may accidentally or unknowingly write `mbox' and not know
we support 4 incompatible mbox variants.
---
 lib/PublicInbox/LeiToMail.pm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/PublicInbox/LeiToMail.pm b/lib/PublicInbox/LeiToMail.pm
index de75e99e..008da52e 100644
--- a/lib/PublicInbox/LeiToMail.pm
+++ b/lib/PublicInbox/LeiToMail.pm
@@ -407,7 +407,9 @@ sub new {
 		$lei->{opt}->{save} //= \1 if $lei->{cmd} eq 'q';
 	} elsif (substr($fmt, 0, 4) eq 'mbox') {
 		require PublicInbox::MboxReader;
-		$self->can("eml2$fmt") or die "bad mbox format: $fmt\n";
+		$self->can("eml2$fmt") or die <<EOM;
+E: bad mbox format: $fmt (did you mean: mboxrd, mboxo, mboxcl, or mboxcl2?)
+EOM
 		$self->{base_type} = 'mbox';
 		if ($lei->{cmd} eq 'q' &&
 				(($lei->path_to_fd($dst) // -1) < 0) &&