From 27a8a9e2a55ccc148582006396a9c35bafa5f0b3 Mon Sep 17 00:00:00 2001
From: David Mitchell <davem@iabyn.com>
Date: Wed, 30 Nov 2016 08:59:01 +0000
Subject: [PATCH] split was leaving PL_sv_undef in unused ary slots
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Petr Pisar: Ported to 5.24.0:

commit 71ca73e5fa9639ac33e9f2e74cd0c32288a5040d
Author: David Mitchell <davem@iabyn.com>
Date:   Wed Nov 30 08:59:01 2016 +0000

    split was leaving PL_sv_undef in unused ary slots

    This:

        @a = split(/-/,"-");
        $a[1] = undef;
        $a[0] = 0;

    was giving

        Modification of a read-only value attempted at foo line 3.

    This is because:

    1) unused slots in AvARRAY between AvFILL and AvMAX should always be
    null; av_clear(), av_extend() etc do this; while av_store(), if storing
    to a slot N somewhere between AvFILL and AvMAX, doesn't bother to clear
    between (AvFILL+1)..(N-1) on the assumption that everyone else plays
    nicely.

    2) pp_split() when splitting directly to an array, sometimes over-splits
    and has to null out the excess elements;

    3) Since perl 5.19.4, unused AV slots are now marked with NULL rather than
    &PL_sv_undef;

    4) pp_split was still using &PL_sv_undef;

    The fault was with (4), and is easily fixed.

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 pp.c         |  2 +-
 t/op/split.t | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/pp.c b/pp.c
index 4153482..70345ce 100644
--- a/pp.c
+++ b/pp.c
@@ -6212,7 +6212,7 @@ PP(pp_split)
 	    while (iters > 0 && (!TOPs || !SvANY(TOPs) || SvCUR(TOPs) == 0)) {
 		if (TOPs && !make_mortal)
 		    sv_2mortal(TOPs);
-		*SP-- = &PL_sv_undef;
+		*SP-- = NULL;
 		iters--;
 	    }
 	}
diff --git a/t/op/split.t b/t/op/split.t
index fb73271..b7846a1 100644
--- a/t/op/split.t
+++ b/t/op/split.t
@@ -7,7 +7,7 @@ BEGIN {
     set_up_inc('../lib');
 }
 
-plan tests => 131;
+plan tests => 133;
 
 $FS = ':';
 
@@ -523,3 +523,14 @@ is "@a", '1 2 3', 'assignment to split-to-array (pmtarget/package array)';
 }
 (@{\@a} = split //, "abc") = 1..10;
 is "@a", '1 2 3', 'assignment to split-to-array (stacked)';
+
+# splitting directly to an array wasn't filling unused AvARRAY slots with
+# NULL
+
+{
+    my @a;
+    @a = split(/-/,"-");
+    $a[1] = 'b';
+    ok eval { $a[0] = 'a'; 1; }, "array split filling AvARRAY: assign 0";
+    is "@a", "a b", "array split filling AvARRAY: result";
+}
-- 
2.7.4