Don’t leak subs containing syntax errors

I fixed this for BEGIN blocks earlier, but missed the fact that
all subs are affected.

When called without an o argument (from newANONATTRSUB), newATTRSUB
is expected to return a CV with an unowned reference count of which
the caller will take ownership.  We cannot have newATTRSUB returning
a freed CV, so we have it return null instead.  But that means
ck_anoncode and pm_runtime have to account for that.

Author: Father Chrysostomos

op.c

@@ -4650,7 +4650,7 @@ Perl_pmruntime(pTHX_ OP *o, OP *expr, bool isreg, I32 floor)
 
 		/* attach the anon CV to the pad so that
 		 * pad_fixup_inner_anons() can find it */
-		(void)pad_add_anon(cv, o->op_type);
+		if (cv) (void)pad_add_anon(cv, o->op_type);
 		SvREFCNT_inc_simple_void(cv);
 	    }
 	    else {
@@ -7370,15 +7370,14 @@ Perl_newATTRSUB_flags(pTHX_ I32 floor, OP *o, OP *proto, OP *attrs,
 
     if (ec) {
 	op_free(block);
-	cv = PL_compcv;
+	SvREFCNT_dec(PL_compcv);
+	PL_compcv = 0;
 	if (name && block) {
 	    const char *s = strrchr(name, ':');
 	    s = s ? s+1 : name;
 	    if (strEQ(s, "BEGIN")) {
 		const char not_safe[] =
 		    "BEGIN not safe after errors--compilation aborted";
-		PL_compcv = 0;
-		SvREFCNT_dec(cv);
 		if (PL_in_eval & EVAL_KEEPERR)
 		    Perl_croak(aTHX_ not_safe);
 		else {
@@ -8176,6 +8175,9 @@ Perl_ck_anoncode(pTHX_ OP *o)
 {
     PERL_ARGS_ASSERT_CK_ANONCODE;
 
+    /* After errors, we won’t have any sub. */
+    if (!cSVOPo->op_sv) return o;
+
     cSVOPo->op_targ = pad_add_anon((CV*)cSVOPo->op_sv, o->op_type);
     if (!PL_madskills)
 	cSVOPo->op_sv = NULL;

t/op/svleak.t

@@ -15,7 +15,7 @@ BEGIN {
 
 use Config;
 
-plan tests => 64;
+plan tests => 65;
 
 # run some code N times. If the number of SVs at the end of loop N is
 # greater than (N-1)*delta at the end of loop 1, we've got a leak
@@ -195,6 +195,7 @@ SKIP: {
 }
 
 eleak(2, 0, '+sub:a{}', 'anon subs with invalid attributes');
+eleak(2, 0, 'no warnings; sub a{1 1}', 'sub with syntax error');
 
 # Syntax errors
 eleak(2, 0, '"${<<END}"