Fix: in Rails 3 HashWithIndifferentAccess doesn't convert nested Hashes.

lib/grape.rb

@@ -82,6 +82,7 @@ module Extensions
 
     autoload :DeepMergeableHash
     autoload :DeepSymbolizeHash
+    autoload :DeepHashWithIndifferentAccess
     autoload :Hash
 
     module ActiveSupport

lib/grape/extensions/active_support/hash_with_indifferent_access.rb

@@ -2,21 +2,22 @@ module Grape
   module Extensions
     module ActiveSupport
       module HashWithIndifferentAccess
-        extend ::ActiveSupport::Concern
+        module ParamBuilder
+          extend ::ActiveSupport::Concern
 
-        included do
-          namespace_inheritable(:build_params_with, Grape::Extensions::ActiveSupport::HashWithIndifferentAccess::ParamBuilder)
-        end
+          included do
+            namespace_inheritable(:build_params_with, Grape::Extensions::ActiveSupport::HashWithIndifferentAccess::ParamBuilder)
+          end
 
-        def params_builder
-          Grape::Extensions::ActiveSupport::HashWithIndifferentAccess::ParamBuilder
-        end
+          def params_builder
+            Grape::Extensions::ActiveSupport::HashWithIndifferentAccess::ParamBuilder
+          end
 
-        module ParamBuilder
           def build_params
             params = ::ActiveSupport::HashWithIndifferentAccess[rack_params]
             params.deep_merge!(grape_routing_args) if env[Grape::Env::GRAPE_ROUTING_ARGS]
-            params
+            # TODO: remove, in Rails 4 or later ::ActiveSupport::HashWithIndifferentAccess converts nested Hashes into indifferent access ones
+            DeepHashWithIndifferentAccess.deep_hash_with_indifferent_access(params)
           end
         end
       end

lib/grape/extensions/deep_hash_with_indifferent_access.rb

@@ -0,0 +1,18 @@
+module Grape
+  module Extensions
+    module DeepHashWithIndifferentAccess
+      def self.deep_hash_with_indifferent_access(object)
+        case object
+        when ::Hash
+          object.inject(::ActiveSupport::HashWithIndifferentAccess.new) do |new_hash, (key, value)|
+            new_hash.merge!(key => deep_hash_with_indifferent_access(value))
+          end
+        when ::Array
+          object.map { |element| deep_hash_with_indifferent_access(element) }
+        else
+          object
+        end
+      end
+    end
+  end
+end

lib/grape/extensions/deep_symbolize_hash.rb

@@ -15,7 +15,15 @@ def self.deep_symbolize_keys_in(object)
       end
 
       def self.symbolize_key(key)
-        key.respond_to?(:to_sym) ? key.to_sym : key
+        if key.is_a?(Symbol)
+          key
+        elsif key.is_a?(String)
+          key.to_sym
+        elsif key.respond_to?(:to_sym)
+          key.to_sym
+        else
+          key
+        end
       end
     end
   end