From 9146d5c34fa58a9680c1d8b85e34244b3608887b Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby-lang.org>
Date: Sat, 19 Aug 2017 11:11:26 +0900
Subject: Zero width `unshift` should not touch memory; ref #3780

---
 src/array.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

(limited to 'src/array.c')

diff --git a/src/array.c b/src/array.c
index cec08b351..be6744724 100644
--- a/src/array.c
+++ b/src/array.c
@@ -562,6 +562,10 @@ mrb_ary_unshift_m(mrb_state *mrb, mrb_value self)
   mrb_int alen, len;
 
   mrb_get_args(mrb, "*!", &vals, &alen);
+  if (alen == 0) {
+    ary_modify_check(mrb, a);
+    return self;
+  }
   len = ARY_LEN(a);
   if (alen > ARY_MAX_SIZE - len) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "array size too big");
@@ -575,7 +579,6 @@ mrb_ary_unshift_m(mrb_state *mrb, mrb_value self)
   }
   else {
     ary_modify(mrb, a);
-    if (alen == 0) return self;
     if (ARY_CAPA(a) < len + alen)
       ary_expand_capa(mrb, a, len + alen);
     ptr = ARY_PTR(a);
-- 
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