hash.c: fix segv in Hash#replace

* hash.c (rb_hash_replace): fix segv on `{}.replace({})` introduced
  in r44060 [Bug #9230] [ruby-core:58991]
* test/ruby/test_hash.rb: regression test for above

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44096 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Mon Dec  9 18:50:43 2013  Aman Gupta <ruby@tmm1.net>
+
+	* hash.c (rb_hash_replace): fix segv on `{}.replace({})` introduced
+	  in r44060 [Bug #9230] [ruby-core:58991]
+	* test/ruby/test_hash.rb: regression test for above
+
 Mon Dec  9 18:10:10 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* vm.c (vm_stat): renamed from ruby_vm_stat.

hash.c

@@ -1414,7 +1414,7 @@ rb_hash_replace(VALUE hash, VALUE hash2)
     table2 = RHASH(hash2)->ntbl;
 
     rb_hash_clear(hash);
-    hash_tbl(hash)->type = table2->type;
+    if (table2) hash_tbl(hash)->type = table2->type;
     rb_hash_foreach(hash2, replace_i, hash);
 
     return hash;

test/ruby/test_hash.rb

@@ -592,6 +592,16 @@ class TestHash < Test::Unit::TestCase
     assert_nil(h[2])
   end
 
+  def test_replace_bug9230
+    h = @cls[]
+    h.replace(@cls[])
+    assert_empty h
+
+    h = @cls[]
+    h.replace(@cls[].compare_by_identity)
+    assert_predicate(h, :compare_by_identity?)
+  end
+
   def test_shift
     h = @h.dup