Reset index before iterating

Add reset_index to facilitate

lib/grape/validations/attributes_iterator.rb

@@ -21,6 +21,7 @@ def each(&block)
       private
 
       def do_each(params_to_process, parent_indicies = [], &block)
+        @scope.reset_index # gets updated depending on the size of params_to_process
         params_to_process.each_with_index do |resource_params, index|
           # when we get arrays of arrays it means that target element located inside array
           # we need this because we want to know parent arrays indicies

lib/grape/validations/params_scope.rb

@@ -169,6 +169,10 @@ def required?
         !@optional
       end
 
+      def reset_index
+        @index = nil
+      end
+
       protected
 
       # Adds a parameter declaration to our list of validations.

spec/grape/validations_spec.rb

@@ -1988,6 +1988,48 @@ def validate_param!(attr_name, params)
         expect(last_response.status).to eq(400)
       end
     end
+
+    # Ensure there is no leakage of indices between requests
+    context 'required with a hash inside an array' do
+      before do
+        subject.params do
+          requires :items, type: Array do
+            requires :item, type: Hash do
+              requires :name, type: String
+            end
+          end
+        end
+        subject.post '/required' do
+          'required works'
+        end
+      end
+
+      let(:valid_item) { { item: { name: 'foo' } } }
+
+      let(:params) do
+        {
+          items: [
+            valid_item,
+            valid_item,
+            {}
+          ]
+        }
+      end
+
+      it 'makes sure the error message is independent of the previous request' do
+        post_with_json '/required', {}
+        expect(last_response).to be_bad_request
+        expect(last_response.body).to eq('items is missing, items[item][name] is missing')
+
+        post_with_json '/required', params
+        expect(last_response).to be_bad_request
+        expect(last_response.body).to eq('items[2][item] is missing, items[2][item][name] is missing')
+
+        post_with_json '/required', {}
+        expect(last_response).to be_bad_request
+        expect(last_response.body).to eq('items is missing, items[item][name] is missing')
+      end
+    end
   end
 
   describe 'require_validator' do