From 38882aeceed1a9802ba242c947bb60bb7746897c Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Mon, 7 Jul 2025 14:30:42 +0900
Subject: [PATCH] array.c: add recursion detection to Array#== and Array#eql?

Prevent SystemStackError when comparing arrays with circular references.
Uses the same recursion detection mechanism as Hash equality methods.

Co-authored-by: Claude <noreply@anthropic.com>
---
 src/array.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/array.c b/src/array.c
index 7b74aaae4..bb4aeb4cf 100644
--- a/src/array.c
+++ b/src/array.c
@@ -1669,6 +1669,11 @@ mrb_ary_eq(mrb_state *mrb, mrb_value ary1)
   if (n == 1) return mrb_true_value();
   if (n == 0) return mrb_false_value();
 
+  /* Check for recursion */
+  if (MRB_RECURSIVE_BINARY_P(mrb, MRB_OPSYM(eq), ary1, ary2)) {
+    return mrb_false_value();
+  }
+
   int ai = mrb_gc_arena_save(mrb);
   for (mrb_int i=0; i<RARRAY_LEN(ary1); i++) {
     mrb_value eq = mrb_funcall_id(mrb, mrb_ary_entry(ary1, i), MRB_OPSYM(eq), 1, mrb_ary_entry(ary2, i));
@@ -1695,6 +1700,11 @@ mrb_ary_eql(mrb_state *mrb, mrb_value ary1)
   if (n == 1) return mrb_true_value();
   if (n == 0) return mrb_false_value();
 
+  /* Check for recursion */
+  if (MRB_RECURSIVE_BINARY_P(mrb, MRB_SYM_Q(eql), ary1, ary2)) {
+    return mrb_false_value();
+  }
+
   int ai = mrb_gc_arena_save(mrb);
   for (mrb_int i=0; i<RARRAY_LEN(ary1); i++) {
     mrb_value eq = mrb_funcall_id(mrb, mrb_ary_entry(ary1, i), MRB_SYM_Q(eql), 1, mrb_ary_entry(ary2, i));