From 031c6d827a20d62a99481765d8e1b1686025aa2b Mon Sep 17 00:00:00 2001
From: Father Chrysostomos <sprout@cpan.org>
Date: Wed, 28 Aug 2013 18:34:22 -0700
Subject: [PATCH] Make vivify_defelem allow &PL_sv_undef array entries
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This is something I failed to change in commit ce0d59f.  I don’t know
of a way to trigger this in pure-Perl code, hence the use of XS in
the test.  It did show up in pure-Perl code due to a bug fixed by the
previous commit.
---
 ext/XS-APItest/APItest.xs |  5 +++++
 mg.c                      |  2 +-
 t/op/for.t                | 13 ++++++++++++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/ext/XS-APItest/APItest.xs b/ext/XS-APItest/APItest.xs
index 2db7b4f..38d4364 100644
--- a/ext/XS-APItest/APItest.xs
+++ b/ext/XS-APItest/APItest.xs
@@ -3462,6 +3462,11 @@ sv_mortalcopy(SV *sv)
 SV *
 newRV(SV *sv)
 
+void
+alias_av(AV *av, IV ix, SV *sv)
+    CODE:
+	av_store(av, ix, SvREFCNT_inc(sv));
+
 MODULE = XS::APItest PACKAGE = XS::APItest::AUTOLOADtest
 
 int
diff --git a/mg.c b/mg.c
index 604fe6b..543af81 100644
--- a/mg.c
+++ b/mg.c
@@ -2381,7 +2381,7 @@ Perl_vivify_defelem(pTHX_ SV *sv)
 	    LvTARG(sv) = NULL;	/* array can't be extended */
 	else {
 	    SV* const * const svp = av_fetch(av, LvSTARGOFF(sv), TRUE);
-	    if (!svp || (value = *svp) == &PL_sv_undef)
+	    if (!svp || !(value = *svp))
 		Perl_croak(aTHX_ PL_no_aelem, LvSTARGOFF(sv));
 	}
     }
diff --git a/t/op/for.t b/t/op/for.t
index 6cd0224..18fedeb 100644
--- a/t/op/for.t
+++ b/t/op/for.t
@@ -4,7 +4,7 @@ BEGIN {
     require "test.pl";
 }
 
-plan(105);
+plan(106);
 
 # A lot of tests to check that reversed for works.
 
@@ -568,3 +568,14 @@ sub {
         is eval { \$_ }, \undef, 'foreach (@array_containing_undef)'
     }
 }->(undef);
+
+SKIP: {
+    skip "No XS::APItest under miniperl", 1, if is_miniperl;
+    my @a;
+    sub {
+        require XS::APItest;
+        XS::APItest::alias_av(\@a, 0, undef);
+        eval { \$_[0] }
+    }->($a[0]);
+    is $@, "", 'vivify_defelem does not croak on &PL_sv_undef elements';
+}
-- 
2.7.4