don't mistake tr/// for assignable reference

For the lhs of an assignment to be an assignable srefgen, the
srefgen must be its top-level op.  ck_refassign() asserted that, but
S_assignment_type() was delving inside a null op looking for the srefgen,
the same way it looks for things that distinguish between scalar and
list assignment.  This showed up in a weird situation where a no-op
transliteration could be applied to an srefgen, getting an srefgen inside
a null op.  Fixes [perl #130578].

1 files changed, 17 insertions, 17 deletions

diff --git a/op.c b/op.c
index 072d3ceb53..a27e4b14db 100644
--- a/op.c
+++ b/op.c
@@ -7579,11 +7579,24 @@ S_assignment_type(pTHX_ const OP *o)
     if (!o)
 	return TRUE;
 
-    if ((o->op_type == OP_NULL) && (o->op_flags & OPf_KIDS))
-	o = cUNOPo->op_first;
+    if (o->op_type == OP_SREFGEN)
+    {
+	OP * const kid = cUNOPx(cUNOPo->op_first)->op_first;
+	type = kid->op_type;
+	flags = o->op_flags | kid->op_flags;
+	if (!(flags & OPf_PARENS)
+	  && (kid->op_type == OP_RV2AV || kid->op_type == OP_PADAV ||
+	      kid->op_type == OP_RV2HV || kid->op_type == OP_PADHV ))
+	    return ASSIGN_REF;
+	ret = ASSIGN_REF;
+    } else {
+	if ((o->op_type == OP_NULL) && (o->op_flags & OPf_KIDS))
+	    o = cUNOPo->op_first;
+	flags = o->op_flags;
+	type = o->op_type;
+	ret = 0;
+    }
 
-    flags = o->op_flags;
-    type = o->op_type;
     if (type == OP_COND_EXPR) {
         OP * const sib = OpSIBLING(cLOGOPo->op_first);
         const I32 t = assignment_type(sib);
@@ -7596,19 +7609,6 @@ S_assignment_type(pTHX_ const OP *o)
 	return FALSE;
     }
 
-    if (type == OP_SREFGEN)
-    {
-	OP * const kid = cUNOPx(cUNOPo->op_first)->op_first;
-	type = kid->op_type;
-	flags |= kid->op_flags;
-	if (!(flags & OPf_PARENS)
-	  && (kid->op_type == OP_RV2AV || kid->op_type == OP_PADAV ||
-	      kid->op_type == OP_RV2HV || kid->op_type == OP_PADHV ))
-	    return ASSIGN_REF;
-	ret = ASSIGN_REF;
-    }
-    else ret = 0;
-
     if (type == OP_LIST &&
 	(flags & OPf_WANT) == OPf_WANT_SCALAR &&
 	o->op_private & OPpLVAL_INTRO)