[perl #121827] Fix repeat stack bugs

(...)x... is marked as a list at compile time and given a pushmark,
before the context is known.  If it turns out to be called in scalar
or void context after all, then pp_repeat has to handle the mark that
has been pushed on to the markstack.

It was not handling the mark for overloading.  Nor was it handling
void context correctly at all.  (The stack may have an empty list, in
which case we call FETCH on a potentially tied stack item that has
nothing to do with us.)

I tested it in void context, because I plan to undo the listification
when scalar context is applied, for speed.

lib/overload.t

@@ -48,7 +48,7 @@ package main;
 
 $| = 1;
 BEGIN { require './test.pl' }
-plan tests => 5198;
+plan tests => 5199;
 
 use Scalar::Util qw(tainted);
 
@@ -2748,6 +2748,12 @@ package refsgalore {
     is ioref->(), 46, '(overloaded constant that is not a sub ref)->()';
 }
 
+package xstack { use overload 'x' => sub { shift . " x " . shift },
+                              '""'=> sub { "xstack" } }
+is join(",", 1..3, scalar((bless([], 'xstack')) x 3, 1), 4..6),
+  "1,2,3,1,4,5,6",
+  '(...)x... in void cx with x overloaded [perl #121827]';
+
 { # undefining the overload stash -- KEEP THIS TEST LAST
     package ant;
     use overload '+' => 'onion';

pp.c

@@ -1650,6 +1650,25 @@ PP(pp_repeat)
 	SvGETMAGIC(sv);
     }
     else {
+	if (UNLIKELY(PL_op->op_private & OPpREPEAT_DOLIST)) {
+	    /* The parser saw this as a list repeat, and there
+	       are probably several items on the stack. But we're
+	       in scalar/void context, and there's no pp_list to save us
+	       now. So drop the rest of the items -- robin@kitsite.com
+	     */
+	    dMARK;
+	    if (MARK + 1 < SP) {
+		MARK[1] = TOPm1s;
+		MARK[2] = TOPs;
+	    }
+	    else {
+		dTOPss;
+		ASSUME(MARK + 1 == SP);
+		XPUSHs(sv);
+		MARK[1] = &PL_sv_undef;
+	    }
+	    SP = MARK + 2;
+	}
 	tryAMAGICbin_MG(repeat_amg, AMGf_assign);
 	sv = POPs;
     }
@@ -1741,15 +1760,6 @@ PP(pp_repeat)
 	else
 	    (void)SvPOK_only(TARG);
 
-	if (PL_op->op_private & OPpREPEAT_DOLIST) {
-	    /* The parser saw this as a list repeat, and there
-	       are probably several items on the stack. But we're
-	       in scalar context, and there's no pp_list to save us
-	       now. So drop the rest of the items -- robin@kitsite.com
-	     */
-	    dMARK;
-	    SP = MARK;
-	}
 	PUSHTARG;
     }
     RETURN;

t/op/repeat.t

@@ -6,7 +6,7 @@ BEGIN {
 }
 
 require './test.pl';
-plan(tests => 46);
+plan(tests => 47);
 
 # compile time
 
@@ -141,6 +141,16 @@ is($y, undef,   '  no extra values on stack');
 # operand of the eq binop needs to remain!
 is(77, scalar ((1,7)x2),    'stack truncation');
 
+# ( )x in void context should not read preceding stack items
+package Tiecount {
+    sub TIESCALAR { bless[]} sub FETCH { our $Tiecount++; study; 3 }
+}
+sub nil {}
+tie my $t, "Tiecount";
+{ push my @temp, $t, scalar((nil) x 3, 1) }
+is($Tiecount::Tiecount, 1,
+   '(...)x... in void context in list (via scalar comma)');
+
 
 # perlbug 20011113.110 works in 5.6.1, broken in 5.7.2
 {