From 319ac31529eb7bf7e5a4ef582c6f930bd8fca62e Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Thu, 28 Nov 2024 15:13:52 +0900
Subject: [PATCH] Assert that non-empty LINK_ANCHOR does not loop

After any `LINK_ELEMENT` sequence is added, `LINK_ANCHOR` must not
loop.
---
 compile.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/compile.c b/compile.c
index 7de791a033..bd691627e3 100644
--- a/compile.c
+++ b/compile.c
@@ -1290,10 +1290,15 @@ static void
 APPEND_LIST(ISEQ_ARG_DECLARE LINK_ANCHOR *const anc1, LINK_ANCHOR *const anc2)
 {
     if (anc2->anchor.next) {
+        /* LINK_ANCHOR must not loop */
+        RUBY_ASSERT(anc2->last != &anc2->anchor);
         anc1->last->next = anc2->anchor.next;
         anc2->anchor.next->prev = anc1->last;
         anc1->last = anc2->last;
     }
+    else {
+        RUBY_ASSERT(anc2->last == &anc2->anchor);
+    }
     verify_list("append", anc1);
 }
 #if CPDEBUG < 0