From 923a39c59285eb06a7c6ca4ce01d2cec711fcfac Mon Sep 17 00:00:00 2001
From: Tony Cook <tony@develop-help.com>
Date: Wed, 21 Apr 2021 13:47:49 +1000
Subject: [PATCH] workaround unexpected op trees generated by Data::Alias

Data::Alias can produce intermediate leave ops that don't have the
expected:

  leave
     enter
     moreops

structure, which breaks in Perl_scalar() and Perl_list() with the
new(ish) non-recursive crawl of the OP tree permitted with
PERL_OP_PARENT.

This doesn't fix a more recent parsing issue.
---
 op.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/op.c b/op.c
index 594d4ee9c329..45d50f77fb22 100644
--- a/op.c
+++ b/op.c
@@ -1964,6 +1964,11 @@ Perl_scalar(pTHX_ OP *o)
         case OP_LEAVETRY:
             kid = cLISTOPo->op_first;
             scalar(kid);
+            if (!OpHAS_SIBLING(kid)) {
+                /* handle broken leave trees */
+                next_kid = kid;
+                goto do_next;
+            }
             kid = OpSIBLING(kid);
         do_kids:
             while (kid) {
@@ -2552,6 +2557,11 @@ Perl_list(pTHX_ OP *o)
         case OP_LEAVETRY:
             kid = cLISTOPo->op_first;
             list(kid);
+            if (!OpHAS_SIBLING(kid)) {
+                /* handle broken leave trees */
+                next_kid = kid;
+                goto do_next;
+            }
             kid = OpSIBLING(kid);
         do_kids:
             while (kid) {