1 files changed, 35 insertions, 12 deletions
diff --git a/actionpack/lib/action_controller/metal/strong_parameters.rb b/actionpack/lib/action_controller/metal/strong_parameters.rb
index ae600b1ebe..d86d49c9dc 100644
--- a/actionpack/lib/action_controller/metal/strong_parameters.rb
+++ b/actionpack/lib/action_controller/metal/strong_parameters.rb
@@ -3,6 +3,7 @@ require 'active_support/core_ext/array/wrap'
 require 'active_support/rescuable'
 require 'action_dispatch/http/upload'
 require 'stringio'
+require 'set'
 
 module ActionController
   # Raised when a required parameter is missing.
@@ -17,7 +18,7 @@ module ActionController
 
     def initialize(param) # :nodoc:
       @param = param
-      super("param not found: #{param}")
+      super("param is missing or the value is empty: #{param}")
     end
   end
 
@@ -31,7 +32,7 @@ module ActionController
 
     def initialize(params) # :nodoc:
       @params = params
-      super("found unpermitted parameters: #{params.join(", ")}")
+      super("found unpermitted parameter#{'s' if params.size > 1 }: #{params.join(", ")}")
     end
   end
 
@@ -125,6 +126,13 @@ module ActionController
       @permitted = self.class.permit_all_parameters
     end
 
+    # Attribute that keeps track of converted arrays, if any, to avoid double
+    # looping in the common use case permit + mass-assignment. Defined in a
+    # method to instantiate it only if needed.
+    def converted_arrays
+      @converted_arrays ||= Set.new
+    end
+
     # Returns +true+ if the parameter is permitted, +false+ otherwise.
     #
     #   params = ActionController::Parameters.new
@@ -149,8 +157,10 @@ module ActionController
     #   Person.new(params) # => #<Person id: nil, name: "Francesco">
     def permit!
       each_pair do |key, value|
-        convert_hashes_to_parameters(key, value)
-        self[key].permit! if self[key].respond_to? :permit!
+        value = convert_hashes_to_parameters(key, value)
+        Array.wrap(value).each do |_|
+          _.permit! if _.respond_to? :permit!
+        end
       end
 
       @permitted = true
@@ -284,7 +294,7 @@ module ActionController
     #   params.fetch(:none, 'Francesco')    # => "Francesco"
     #   params.fetch(:none) { 'Francesco' } # => "Francesco"
     def fetch(key, *args)
-      convert_hashes_to_parameters(key, super)
+      convert_hashes_to_parameters(key, super, false)
     rescue KeyError
       raise ActionController::ParameterMissing.new(key)
     end
@@ -322,19 +332,28 @@ module ActionController
       end
 
     private
-      def convert_hashes_to_parameters(key, value)
-        if value.is_a?(Parameters) || !value.is_a?(Hash)
+      def convert_hashes_to_parameters(key, value, assign_if_converted=true)
+        converted = convert_value_to_parameters(value)
+        self[key] = converted if assign_if_converted && !converted.equal?(value)
+        converted
+      end
+
+      def convert_value_to_parameters(value)
+        if value.is_a?(Array) && !converted_arrays.member?(value)
+          converted = value.map { |_| convert_value_to_parameters(_) }
+          converted_arrays << converted
+          converted
+        elsif value.is_a?(Parameters) || !value.is_a?(Hash)
           value
         else
-          # Convert to Parameters on first access
-          self[key] = self.class.new(value)
+          self.class.new(value)
         end
       end
 
       def each_element(object)
         if object.is_a?(Array)
           object.map { |el| yield el }.compact
-        elsif object.is_a?(Hash) && object.keys.all? { |k| k =~ /\A-?\d+\z/ }
+        elsif fields_for_style?(object)
           hash = object.class.new
           object.each { |k,v| hash[k] = yield v }
           hash
@@ -343,6 +362,10 @@ module ActionController
         end
       end
 
+      def fields_for_style?(object)
+        object.is_a?(Hash) && object.all? { |k, v| k =~ /\A-?\d+\z/ && v.is_a?(Hash) }
+      end
+
       def unpermitted_parameters!(params)
         unpermitted_keys = unpermitted_keys(params)
         if unpermitted_keys.any?
@@ -421,7 +444,7 @@ module ActionController
 
         # Slicing filters out non-declared keys.
         slice(*filter.keys).each do |key, value|
-          return unless value
+          next unless value
 
           if filter[key] == EMPTY_ARRAY
             # Declaration { comment_ids: [] }.
@@ -479,7 +502,7 @@ module ActionController
   #       end
   #   end
   #
-  # In order to use <tt>accepts_nested_attribute_for</tt> with Strong \Parameters, you
+  # In order to use <tt>accepts_nested_attributes_for</tt> with Strong \Parameters, you
   # will need to specify which nested attributes should be whitelisted.
   #
   #   class Person