Raise an error when AS::JSON.decode is called with options

Rails 4.1 has switched away from MultiJson, and does not currently
support any options on `ActiveSupport::JSON.decode`. Passing in
unsupported options (i.e. any non-empty options hash) will now raise
an ArgumentError.

Rationale:

1. We cannot guarantee the underlying JSON parser won't change in the
   future, hence we cannot guarantee a consistent set of options the
   method could take

2. The `json` gem, which happens to be the current JSON parser, takes
   many dangerous options that is irrelevant to the purpose of AS's
   JSON decoding API

3. To reserve the options hash for future use, e.g. overriding default
   global options like ActiveSupport.parse_json_times

This change *DOES NOT* introduce any changes in the public API. The
signature of the method is still decode(json_text, options). The
difference is this method previously accepted undocumented options
which does different things when the underlying adapter changes. It
now correctly raises an ArgumentError when it encounters options that
it does not recognize (and currently it does not support any options).

3 files changed, 14 insertions, 5 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 25667af101..2d934f8bc4 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Calling ActiveSupport::JSON.decode with unsupported options now raises an error.
+
+    *Godfrey Chan*
+
 *   Support :unless_exist in FileStore
 
     *Michael Grosser*
diff --git a/activesupport/lib/active_support/json/decoding.rb b/activesupport/lib/active_support/json/decoding.rb
index 21de09c1cc..315c76199a 100644
--- a/activesupport/lib/active_support/json/decoding.rb
+++ b/activesupport/lib/active_support/json/decoding.rb
@@ -14,7 +14,14 @@ module ActiveSupport
       #   ActiveSupport::JSON.decode("{\"team\":\"rails\",\"players\":\"36\"}")
       #   => {"team" => "rails", "players" => "36"}
       def decode(json, options = {})
-        data = ::JSON.parse(json, options.merge(create_additions: false, quirks_mode: true))
+        if options.present?
+          raise ArgumentError, "In Rails 4.1, ActiveSupport::JSON.decode no longer " \
+            "accepts an options hash for MultiJSON. MultiJSON reached its end of life " \
+            "and has been removed."
+        end
+
+        data = ::JSON.parse(json, quirks_mode: true)
+
         if ActiveSupport.parse_json_times
           convert_dates_from(data)
         else
diff --git a/activesupport/test/json/decoding_test.rb b/activesupport/test/json/decoding_test.rb
index e9780b36e4..07d7e530ca 100644
--- a/activesupport/test/json/decoding_test.rb
+++ b/activesupport/test/json/decoding_test.rb
@@ -98,10 +98,8 @@ class TestJSONDecoding < ActiveSupport::TestCase
     assert_raise(ActiveSupport::JSON.parse_error) { ActiveSupport::JSON.decode(%()) }
   end
 
-  def test_cannot_force_json_unmarshalling
-    encodeded = %q({"json_class":"TestJSONDecoding::Foo"})
-    decodeded = {"json_class"=>"TestJSONDecoding::Foo"}
-    assert_equal decodeded, ActiveSupport::JSON.decode(encodeded, create_additions: true)
+  def test_cannot_pass_unsupported_options
+    assert_raise(ArgumentError) { ActiveSupport::JSON.decode("", create_additions: true) }
   end
 end