Freeze hash literals embedded in duphash instructions

Previously, these hash literals were not frozen, and thus could be
modified by ObjectSpace, resulting in undesired behavior.  Example:

```ruby
require 'objspace'

def a(b={0=>1,1=>4,2=>17})
  b
end

p a
ObjectSpace.each_object(Hash) do |a|
  a[3] = 8 if a.class == Hash && a[0] == 1 && a[1] == 4 && a[2] == 17
end
p a
```

It may be desirable to hide such hashes from ObjectSpace, since
they are internal, but I'm not sure how to do that.

From: Jeremy Evans <code@jeremyevans.net>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66464 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 17 insertions, 0 deletions

diff --git a/compile.c b/compile.c
index 731b05323b..cb168438d8 100644
--- a/compile.c
+++ b/compile.c
@@ -4026,6 +4026,7 @@ compile_array(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node_ro
 
                             hash = rb_hash_new_with_size(RARRAY_LEN(ary) / 2);
                             rb_hash_bulk_insert(RARRAY_LEN(ary), RARRAY_CONST_PTR_TRANSIENT(ary), hash);
+                            rb_hash_freeze(hash);
                             iseq_add_mark_object_compile_time(iseq, hash);
                             ADD_INSN1(ret, line, duphash, hash);
 			}
diff --git a/test/ruby/test_literal.rb b/test/ruby/test_literal.rb
index ef2467e177..37755422a1 100644
--- a/test/ruby/test_literal.rb
+++ b/test/ruby/test_literal.rb
@@ -283,6 +283,22 @@ class TestRubyLiteral < Test::Unit::TestCase
     assert_equal "literal", h["string"]
   end
 
+  def frozen_hash_literal_arg
+    {0=>1,1=>4,2=>17}
+  end
+
+  def test_hash_literal_frozen
+    assert_not_include frozen_hash_literal_arg, 3
+    assert_raise(FrozenError) do
+      ObjectSpace.each_object(Hash) do |a|
+        if a.class == Hash and !a.default_proc and a.size == 3
+          a[3] = 8 if a[0] == 1 and a[1] == 4 and a[2] == 17
+        end
+      end
+    end
+    assert_not_include frozen_hash_literal_arg, 3
+  end
+
   def test_big_array_and_hash_literal
     assert_normal_exit %q{GC.disable=true; x = nil; raise if eval("[#{(1..1_000_000).map{'x'}.join(", ")}]").size != 1_000_000}, "", timeout: 300, child_env: %[--disable-gems]
     assert_normal_exit %q{GC.disable=true; x = nil; raise if eval("[#{(1..1_000_000).to_a.join(", ")}]").size != 1_000_000}, "", timeout: 300, child_env: %[--disable-gems]