S_newONCEOP/Perl_scalarvoid: skip over padops useless in void context

Prior to this commit, padops associated with OP_ONCE might serve no
purpose in a void context. Since the context is not known at the point
of the OP_ONCE creation, the padops have retained the STATE flag, but
not the LVINTRO flag. This prevented Perl_scalarvoid from warning
"Useless use of private variable in void context".

In this commit, the STATE flag is removed and Perl_scalarvoid modified
such that when a OP_ONCE padop is found in void context, the op_next
pointer on the OP_ONCE is silently modified to skip over the padop.

ext/B/t/optree_varinit.t

@@ -405,8 +405,6 @@ checkOptree ( name	=> 'void context state',
 # 3  <|> once(other->4)[$:2,3] vK/1
 # 4      <$> const[IV 1] s
 # 5      <1> padsv_store[$x:2,3] vKS/LVINTRO,STATE
-#            goto 6
-# 8  <0> padsv[$x:2,3] v/STATE
 # 6  <;> nextstate(main 3 -e:1) v:%,{,fea=15
 # 7  <@> leave[1 ref] vKP/REFC
 EOT_EOT
@@ -415,8 +413,6 @@ EOT_EOT
 # 3  <|> once(other->4)[$:2,3] vK/1
 # 4      <$> const(IV 1) s
 # 5      <1> padsv_store[$x:2,3] vKS/LVINTRO,STATE
-#            goto 6
-# 8  <0> padsv[$x:2,3] v/STATE
 # 6  <;> nextstate(main 3 -e:1) v:%,{,fea=15
 # 7  <@> leave[1 ref] vKP/REFC
 EONT_EONT
@@ -433,7 +429,7 @@ checkOptree ( name	=> 'scalar context state',
 # 5      <0> padsv[$x:2,3] sRM*/LVINTRO,STATE
 # 6      <2> sassign sKS/2
 #            goto 7
-# a  <0> padsv[$x:2,3] s/STATE
+# a  <0> padsv[$x:2,3] s
 # 7  <1> padsv_store[$y:2,3] vKS/LVINTRO
 # 8  <;> nextstate(main 3 -e:1) v:%,{,fea=15
 # 9  <@> leave[1 ref] vKP/REFC
@@ -445,7 +441,7 @@ EOT_EOT
 # 5      <0> padsv[$x:2,3] sRM*/LVINTRO,STATE
 # 6      <2> sassign sKS/2
 #            goto 7
-# a  <0> padsv[$x:2,3] s/STATE
+# a  <0> padsv[$x:2,3] s
 # 7  <1> padsv_store[$y:2,3] vKS/LVINTRO
 # 8  <;> nextstate(main 3 -e:1) v:%,{,fea=15
 # 9  <@> leave[1 ref] vKP/REFC

op.c

@@ -2257,9 +2257,19 @@ Perl_scalarvoid(pTHX_ OP *arg)
         case OP_ASLICE:
         case OP_HELEM:
         case OP_HSLICE:
-            if (!(o->op_private & (OPpLVAL_INTRO|OPpOUR_INTRO)))
-                /* Otherwise it's "Useless use of grep iterator" */
-                useless = OP_DESC(o);
+            if (!(o->op_private & (OPpLVAL_INTRO|OPpOUR_INTRO))) {
+                if ((op_parent(o)->op_type == OP_ONCE) &&
+                    (op_parent(o)->op_next == o)
+                ){
+                    /* An already set "state" OP has been encounted
+                     * and there's no point pushing anything to the
+                     * stack in void context. */
+                    op_parent(o)->op_next = o->op_next;
+                } else {
+                    /* Otherwise it's "Useless use of grep iterator" */
+                    useless = OP_DESC(o);
+                }
+            }
             break;
 
         case OP_SPLIT:
@@ -8597,8 +8607,8 @@ S_newONCEOP(pTHX_ OP *initop, OP *padop)
 {
     const PADOFFSET target = padop->op_targ;
     OP *const nexop = newOP(padop->op_type,
-                            (padop->op_flags & ~(OPf_REF|OPf_MOD|OPf_SPECIAL))
-                            | ((padop->op_private & ~OPpLVAL_INTRO) << 8));
+            (padop->op_flags & ~(OPf_REF|OPf_MOD|OPf_SPECIAL|OPf_WANT))
+            | ((padop->op_private & ~(OPpLVAL_INTRO|OPpPAD_STATE)) << 8));
     OP *const first = newOP(OP_NULL, 0);
     OP *const nullop = newCONDOP(0, first, initop, nexop);
     /* XXX targlex disabled for now; see ticket #124160

t/op/state.t

@@ -9,7 +9,7 @@ BEGIN {
 
 use strict;
 
-plan tests => 164;
+plan tests => 166;
 
 # Before loading feature.pm, test it with CORE::
 ok eval 'CORE::state $x = 1;', 'CORE::state outside of feature.pm scope';
@@ -509,10 +509,12 @@ for (1,2) {
     sub gh_18630H {state %h=(a=>1)}
     my $res = join '', gh_18630H, gh_18630H;
     is($res, "a1a1", 'HASH copied successfully in subroutine exit');
+    is(scalar gh_18630H, 1, 'gh_18630H scalar call returns key count');
 
     sub gh_18630A {state @a = qw(b 2)}
     $res = join '', gh_18630A , gh_18630A;
     is($res, "b2b2", 'ARRAY copied successfully in subroutine exit');
+    is(scalar gh_18630A, 2, 'gh_18630A scalar call returns element count');
 }
 
 __DATA__