mktables: Add error check

+= is not a commutative operator, and so the overloaded version should
not accept the parameters being swapped.

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/unicore/mktables b/lib/unicore/mktables
index 637f296f8c..b97b11f3d7 100644
--- a/lib/unicore/mktables
+++ b/lib/unicore/mktables
@@ -6812,6 +6812,16 @@ sub trace { return main::trace(@_); }
         '+=' => sub {
                         my $self = shift;
                         my $other = shift;
+                        my $reversed = shift;
+
+                        if ($reversed) {
+                            Carp::my_carp_bug("Bad news.  Can't cope with '"
+                            . ref($other)
+                            . ' += '
+                            . ref($self)
+                            . "'.  undef returned.");
+                            return;
+                        }
 
                         return if $self->carp_if_locked;