Added Hashie::Extensions::Mash::ActiveModel for compatibility with Rails 4 Strong Parameters.

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Next
 
-* Your contribution here.
+* [#146](https://github.com/intridea/hashie/issues/146): Mash#respond_to? inconsistent with #method_missing and does not respond to #permitted? - [@dblock](https://github.com/dblock).
+* [#89](https://github.com/intridea/hashie/issues/89): Added Hashie::Extensions::Mash::ActiveModel for compatibility with Rails 4.x Strong Parameters - [@dblock](https://github.com/dblock).
 
 ## 2.1.1 (4/12/2014)
 

README.md

@@ -238,6 +238,16 @@ p[:awesome]    # => NoMethodError
 p[:occupation] # => 'Rubyist'
 ```
 
+### Mash and Rails 4 Strong Parameters
+
+Add the following initializer in config/initializers/mash.rb when using Mash with [Rails 4 Strong Parameters](http://edgeguides.rubyonrails.org/action_controller_overview.html#strong-parameters). This prevents Mash from responding to `:permitted?` and therefore triggering an ActiveModel `ForbiddenAttributesProtection` exception.
+
+```ruby
+class Mash
+  include Hashie::Extensions::Mash::ActiveModel
+end
+```
+
 ## Trash
 
 A Trash is a Dash that allows you to translate keys on initialization.

lib/hashie.rb

@@ -22,5 +22,9 @@ module Hashie
     autoload :StringifyKeys,     'hashie/extensions/key_conversion'
     autoload :SymbolizeKeys,     'hashie/extensions/key_conversion'
     autoload :DeepFetch,         'hashie/extensions/deep_fetch'
+
+    module Mash
+      autoload :ActiveModel,     'hashie/extensions/mash/active_model'
+    end
   end
 end

lib/hashie/extensions/mash/active_model.rb

@@ -0,0 +1,18 @@
+module Hashie
+  module Extensions
+    module Mash
+      # Extends Mash to behave in a way compatible with ActiveModel.
+      module ActiveModel
+        def respond_to?(name, include_private = false)
+          return false if name == :permitted?
+          super
+        end
+
+        def method_missing(name, *args)
+          fail ArgumentError if name == :permitted?
+          super
+        end
+      end
+    end
+  end
+end

lib/hashie/mash.rb

@@ -57,6 +57,7 @@ module Hashie
   class Mash < Hash
     ALLOWED_SUFFIXES = %w(? ! = _)
     include Hashie::PrettyInspect
+
     alias_method :to_s, :inspect
 
     # If you pass in an existing hash, it will
@@ -185,11 +186,15 @@ module Hashie
       self
     end
 
-    # Will return true if the Mash has had a key
-    # set in addition to normal respond_to? functionality.
     def respond_to?(method_name, include_private = false)
-      return true if key?(method_name) || prefix_method?(method_name)
-      super
+      return true if key?(method_name)
+      _, suffix = method_suffix(method_name)
+      case suffix
+      when '=', '?', '!', '_'
+        return true
+      else
+        super
+      end
     end
 
     def prefix_method?(method_name)
@@ -199,17 +204,16 @@ module Hashie
 
     def method_missing(method_name, *args, &blk)
       return self.[](method_name, &blk) if key?(method_name)
-      suffixes_regex = ALLOWED_SUFFIXES.join
-      match = method_name.to_s.match(/(.*?)([#{suffixes_regex}]?)$/)
-      case match[2]
+      name, suffix = method_suffix(method_name)
+      case suffix
       when '='
-        self[match[1]] = args.first
+        self[name] = args.first
       when '?'
-        !!self[match[1]]
+        !!self[name]
       when '!'
-        initializing_reader(match[1])
+        initializing_reader(name)
       when '_'
-        underbang_reader(match[1])
+        underbang_reader(name)
       else
         default(method_name)
       end
@@ -217,6 +221,12 @@ module Hashie
 
     protected
 
+    def method_suffix(method_name)
+      suffixes_regex = ALLOWED_SUFFIXES.join
+      match = method_name.to_s.match(/(.*?)([#{suffixes_regex}]?)$/)
+      [match[1], match[2]]
+    end
+
     def convert_key(key) #:nodoc:
       key.to_s
     end

spec/hashie/mash_spec.rb

@@ -328,9 +328,9 @@ describe Hashie::Mash do
       end
     end
 
-    it 'does not respond to an unknown key with a suffix' do
+    it 'responds to an unknown key with a suffix' do
       %w(= ? ! _).each do |suffix|
-        expect(Hashie::Mash.new(abc: 'def')).not_to be_respond_to(:"xyz#{suffix}")
+        expect(Hashie::Mash.new(abc: 'def')).to be_respond_to(:"xyz#{suffix}")
       end
     end
 
@@ -339,7 +339,12 @@ describe Hashie::Mash do
     end
 
     it 'does not respond to permitted?' do
-      expect(Hashie::Mash.new).not_to be_respond_to(:permitted?)
+      expect(Hashie::Mash.new).to be_respond_to(:permitted?)
+      klass = Class.new(Hashie::Mash) do
+        include Hashie::Extensions::Mash::ActiveModel
+      end
+      expect(klass.new).not_to be_respond_to(:permitted?)
+      expect { klass.new.permitted? }.to raise_error(ArgumentError)
     end
   end