1 files changed, 28 insertions, 0 deletions
diff --git a/actionpack/lib/action_controller/metal/strong_parameters.rb b/actionpack/lib/action_controller/metal/strong_parameters.rb
index 26794c67b7..f101c7b836 100644
--- a/actionpack/lib/action_controller/metal/strong_parameters.rb
+++ b/actionpack/lib/action_controller/metal/strong_parameters.rb
@@ -7,6 +7,7 @@ require 'action_dispatch/http/upload'
 require 'rack/test'
 require 'stringio'
 require 'set'
+require 'yaml'
 
 module ActionController
   # Raised when a required parameter is missing.
@@ -591,6 +592,33 @@ module ActionController
       "<#{self.class} #{@parameters} permitted: #{@permitted}>"
     end
 
+    def self.hook_into_yaml_loading # :nodoc:
+      # Wire up YAML format compatibility with Rails 4.2 and Psych 2.0.8 and 2.0.9+.
+      # Makes the YAML parser call `init_with` when it encounters the keys below
+      # instead of trying its own parsing routines.
+      YAML.load_tags['!ruby/hash-with-ivars:ActionController::Parameters'] = name
+      YAML.load_tags['!ruby/hash:ActionController::Parameters'] = name
+    end
+    hook_into_yaml_loading
+
+    def init_with(coder) # :nodoc:
+      case coder.tag
+      when '!ruby/hash:ActionController::Parameters'
+        # YAML 2.0.8's format where hash instance variables weren't stored.
+        @parameters = coder.map.with_indifferent_access
+        @permitted  = false
+      when '!ruby/hash-with-ivars:ActionController::Parameters'
+        # YAML 2.0.9's Hash subclass format where keys and values
+        # were stored under an elements hash and `permitted` within an ivars hash.
+        @parameters = coder.map['elements'].with_indifferent_access
+        @permitted  = coder.map['ivars'][:@permitted]
+      when '!ruby/object:ActionController::Parameters'
+        # YAML's Object format. Only needed because of the format
+        # backwardscompability above, otherwise equivalent to YAML's initialization.
+        @parameters, @permitted = coder.map['parameters'], coder.map['permitted']
+      end
+    end
+
     def method_missing(method_sym, *args, &block)
       if @parameters.respond_to?(method_sym)
         message = <<-DEPRECATE.squish