From 3e075a7b6c6082aa728c9fd093e42be862bbf700 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby-lang.org>
Date: Fri, 11 Aug 2017 09:21:47 +0900
Subject: Should not call `to_str` in `mrb_vformat`; fix #3773

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

(limited to 'src/error.c')

diff --git a/src/error.c b/src/error.c
index 062282719..cd771dc2d 100644
--- a/src/error.c
+++ b/src/error.c
@@ -269,9 +269,12 @@ mrb_vformat(mrb_state *mrb, const char *format, va_list ap)
 
     if (c == '%') {
       if (*p == 'S') {
+        mrb_value val;
+
         size = p - b - 1;
         mrb_ary_push(mrb, ary, mrb_str_new(mrb, b, size));
-        mrb_ary_push(mrb, ary, va_arg(ap, mrb_value));
+        val = va_arg(ap, mrb_value);
+        mrb_ary_push(mrb, ary, mrb_obj_as_string(mrb, val));
         b = p + 1;
       }
     }
-- 
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