From ee160e68f9fbb518d4f514987a329fc0a2332973 Mon Sep 17 00:00:00 2001
From: nobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sat, 12 Nov 2016 09:43:05 +0000
Subject: [PATCH] class.c: no fstring singleton class

* class.c (singleton_class_of): prohibit fstrings from creating
  singleton classes.
  temporary measure for [ruby-dev:49867] [Bug #12923]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56747 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 class.c                           | 3 +++
 test/-ext-/string/test_fstring.rb | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/class.c b/class.c
index aed3ee42f2..350e2cc31b 100644
--- a/class.c
+++ b/class.c
@@ -1602,6 +1602,9 @@ singleton_class_of(VALUE obj)
 	switch (BUILTIN_TYPE(obj)) {
 	  case T_FLOAT: case T_BIGNUM: case T_SYMBOL:
 	    goto no_singleton;
+	  case T_STRING:
+	    if (FL_TEST_RAW(obj, RSTRING_FSTR)) goto no_singleton;
+	    break;
 	}
     }
 
diff --git a/test/-ext-/string/test_fstring.rb b/test/-ext-/string/test_fstring.rb
index 39ed020892..0514814dd4 100644
--- a/test/-ext-/string/test_fstring.rb
+++ b/test/-ext-/string/test_fstring.rb
@@ -1,8 +1,11 @@
 # frozen_string_literal: false
 require 'test/unit'
 require '-test-/string'
+require_relative '../symbol/noninterned_name'
 
 class Test_String_Fstring < Test::Unit::TestCase
+  include Test_Symbol::NonInterned
+
   def assert_fstring(str)
     fstr = Bug::String.fstring(str)
     yield str
@@ -54,6 +57,12 @@ class Test_String_Fstring < Test::Unit::TestCase
     assert_fstring(str) {|s| assert_send([s, :respond_to?, :foo])}
   end
 
+  def test_singleton_class
+    str = noninterned_name.force_encoding("us-ascii")
+    fstr = Bug::String.fstring(str)
+    assert_raise(RuntimeError) {fstr.singleton_class}
+  end
+
   class S < String
   end