[perl #109570] Fix off-by-1 error in arybase’s lslice

When I wrote that originally, I was treating POPMARK as equivalent to
--*PL_markstack_ptr, rather than *PL_markstack_ptr--.

So I was using the marker for the outer list surrounding the list
slice, and modifying whatever numbers were to be found there, such as
the 3 and 4 in [3, 4, qw(foo bar)[0]].

2 files changed, 4 insertions, 3 deletions

diff --git a/ext/arybase/arybase.xs b/ext/arybase/arybase.xs
index 296733a7cc..68b9cf99cc 100644
--- a/ext/arybase/arybase.xs
+++ b/ext/arybase/arybase.xs
@@ -245,8 +245,8 @@ static OP *ab_pp_basearg(pTHX) {
   count = SP-firstp;
   break;
  case OP_LSLICE:
-  firstp = PL_stack_base + *(PL_markstack_ptr-2)+1;
-  count = TOPMARK - *(PL_markstack_ptr-2);
+  firstp = PL_stack_base + *(PL_markstack_ptr-1)+1;
+  count = TOPMARK - *(PL_markstack_ptr-1);
   if (GIMME != G_ARRAY) {
    firstp += count-1;
    count = 1;
diff --git a/ext/arybase/t/lslice.t b/ext/arybase/t/lslice.t
index c012b84f5e..0db7a078f2 100644
--- a/ext/arybase/t/lslice.t
+++ b/ext/arybase/t/lslice.t
@@ -1,7 +1,7 @@
 use warnings; no warnings 'deprecated';
 use strict;
 
-use Test::More tests => 11;
+use Test::More tests => 12;
 
 our @i4 = (3, 5, 3, 5);
 
@@ -11,6 +11,7 @@ is_deeply [ scalar qw(a b c d e f)[3,4] ], [ qw(b) ];
 is_deeply [ qw(a b c d e f)[3,4,8,9] ], [ qw(a b f), undef ];
 is_deeply [ scalar qw(a b c d e f)[@i4] ], [ qw(c) ];
 is_deeply [ qw(a b c d e f)[@i4] ], [ qw(a c a c) ];
+is_deeply [ 3, 4, qw(a b c d e f)[@i4] ], [ 3, 4, qw(a c a c) ];
 
 is_deeply [ qw(a b c d e f)[-1,-2] ], [ qw(f e) ];
 is_deeply [ qw(a b c d e f)[2,1] ], [ qw(f e) ];