Added param key to ValidationError class

lib/grape/exceptions/validation_error.rb

@@ -1,4 +1,10 @@
 require 'grape/exceptions/base'
 
 class ValidationError < Grape::Exceptions::Base
+  attr_accessor :param
+
+  def initialize(args = {})
+    @param = args[:param].to_s if args.has_key? :param
+    super
+  end
 end

lib/grape/validations/coerce.rb

@@ -12,7 +12,7 @@ def validate_param!(attr_name, params)
         if valid_type?(new_value)
           params[attr_name] = new_value
         else
-          raise ValidationError, :status => 400, :message => "invalid parameter: #{attr_name}"
+          raise ValidationError, :status => 400, :param => attr_name, :message => "invalid parameter: #{attr_name}"
         end
       end
 

lib/grape/validations/presence.rb

@@ -3,7 +3,7 @@ module Validations
     class PresenceValidator < Validator
       def validate_param!(attr_name, params)
         unless params.has_key?(attr_name)
-          raise ValidationError, :status => 400, :message => "missing parameter: #{attr_name}"
+          raise ValidationError, :status => 400, :param => attr_name, :message => "missing parameter: #{attr_name}"
         end
       end
     end

lib/grape/validations/regexp.rb

@@ -4,7 +4,7 @@ module Validations
     class RegexpValidator < SingleOptionValidator
       def validate_param!(attr_name, params)
         if params[attr_name] && !( params[attr_name].to_s =~ @option )
-          raise ValidationError, :status => 400, :message => "invalid parameter: #{attr_name}"
+          raise ValidationError, :status => 400, :param => attr_name, :message => "invalid parameter: #{attr_name}"
         end
       end
     end