From 7582287eb27e6b649789ce31ffdcbbb9ffcaf726 Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Tue, 18 Jun 2019 18:59:49 -0700
Subject: Make String#-@ not freeze receiver if called on unfrozen subclass
 instance

rb_fstring behavior in this case is to freeze the receiver.  I'm
not sure if that should be changed, so this takes the conservative
approach of duping the receiver in String#-@ before passing
to rb_fstring.

Fixes [Bug #15926]
---
 string.c | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'string.c')

diff --git a/string.c b/string.c
index 6bb8a24313..2bf9586e98 100644
--- a/string.c
+++ b/string.c
@@ -2658,6 +2658,9 @@ str_uplus(VALUE str)
 static VALUE
 str_uminus(VALUE str)
 {
+    if (!BARE_STRING_P(str) && !rb_obj_frozen_p(str)) {
+        str = rb_str_dup(str);
+    }
     return rb_fstring(str);
 }
 
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