Teach mro code about null array elements

This is part of ticket #119433.

Commit ce0d49f changed AVs to use NULL for nonexistent elements.  The
mro lookup code was not accounting for that, causing Class::Contract’s
tests to crash (and perhaps other modules, too).

2 files changed, 14 insertions, 1 deletions

diff --git a/t/mro/basic.t b/t/mro/basic.t
index 65090732f7..5625b5190e 100644
--- a/t/mro/basic.t
+++ b/t/mro/basic.t
@@ -8,7 +8,7 @@ BEGIN {
     @INC = '../lib';
     require q(./test.pl);
 }
-plan(tests => 60);
+plan(tests => 61);
 
 require mro;
 
@@ -389,3 +389,9 @@ undef $x; # should use the new DESTROY
 is $destroy_output, "new",
     'Changes to UNIVERSAL::DESTROY invalidate DESTROY caches';
 undef *UNIVERSAL::DESTROY;
+
+{
+    no warnings 'uninitialized';
+    $#_119433::ISA++;
+    pass "no crash when ISA contains nonexistent elements";
+}
diff --git a/t/mro/isa_c3.t b/t/mro/isa_c3.t
index dd129cf442..20ae5f09b4 100644
--- a/t/mro/isa_c3.t
+++ b/t/mro/isa_c3.t
@@ -67,3 +67,10 @@ foreach my $package (qw(klonk urkkk kapow kayo thwacke zzzzzwap whamm)) {
 	object_ok($ref, $class, $package);
     }
 }
+
+package _119433 {
+    use mro 'c3';
+    no warnings 'uninitialized';
+    $#_119433::ISA++;
+    ::pass "no crash when ISA contains nonexistent elements";
+}