Let Psych 2.0.9+ deserialize 2.0.8 serialized parameters.

If we were to serialize an `ActionController::Parameters` on Psych 2.0.8, we'd get:

```yaml
--- !ruby/hash:ActionController::Parameters
key: :value
```

Because 2.0.8 didn't store instance variables, while 2.0.9 did:
https://github.com/tenderlove/psych/commit/8f84ad0fc711a82a1040def861cb121e8985fd4c

That, coupled with 2.0.8 calling `new` instead of `allocate` meant parameters was
deserialized just fine:
https://github.com/tenderlove/psych/commit/af308f8307899cb9e1c0fffea4bce3110a1c3926

However, if users have 2.0.8 serialized parameters, then upgrade to Psych 2.0.9+ and
Rails 5, it would start to blow up because `initialize` will never be called, and thus
`@parameters` will never be assigned. Hello, `NoMethodErrors` on `NilClass`! :)

To fix this we register another variant of the previous serialization format and take
it into account in `init_with`.

I've tested this in our app and previously raising code now deserializes like a champ.
I'm unsure how to test this in our suite because we use Psych 2.0.8 and don't know how
to make us use 2.0.9+ for just one test.

1 files changed, 15 insertions, 2 deletions

diff --git a/actionpack/test/controller/parameters/serialization_test.rb b/actionpack/test/controller/parameters/serialization_test.rb
index 5d389f5a4c..84193e304a 100644
--- a/actionpack/test/controller/parameters/serialization_test.rb
+++ b/actionpack/test/controller/parameters/serialization_test.rb
@@ -20,13 +20,26 @@ class ParametersSerializationTest < ActiveSupport::TestCase
     assert_not roundtripped.permitted?
   end
 
-  test 'yaml backwardscompatible with hash inheriting parameters' do
-    assert_equal ActionController::Parameters.new(key: :value), YAML.load(<<-end_of_yaml.strip_heredoc)
+  test 'yaml backwardscompatible with psych 2.0.8 format' do
+    params = YAML.load <<-end_of_yaml.strip_heredoc
+      --- !ruby/hash:ActionController::Parameters
+      key: :value
+    end_of_yaml
+
+    assert_equal :value, params[:key]
+    assert_not params.permitted?
+  end
+
+  test 'yaml backwardscompatible with psych 2.0.9+ format' do
+    params = YAML.load(<<-end_of_yaml.strip_heredoc)
       --- !ruby/hash-with-ivars:ActionController::Parameters
       elements:
         key: :value
       ivars:
         :@permitted: false
     end_of_yaml
+
+    assert_equal :value, params[:key]
+    assert_not params.permitted?
   end
 end