Fix reference creation when two types are provided

Previously the type from param definition would be used to documentation
even if we try to override it in the `documentation` hash.
It caused Swagger UI to render, for example, "Unknown Type: Color"
instead of using the provided entity.

It terms of code, before this change we would return something like this:
{ color: { type: 'Color' }
instead of:
{ color: { '$ref' => 'ColorEntity' }
if Color is not inherited from Grape::Entity

Having different types can be useful when two different classes
are used for parsing and presenting an attribute.
E.g. the input format for Base64 File can be represented as a Hash (content,
content_type and filename), whereas the type after parsing can be
ActionDispatch::Http::UploadedFile.

In the current situation the solution to this problem is to put coercion
methods to the same entity and specify `type` only for the param without
using `documentation`.

Author: bikolya

CHANGELOG.md

@@ -6,7 +6,7 @@
 
 #### Fixes
 
-* Your contribution here.
+* [#756](https://github.com/ruby-grape/grape-swagger/pull/756): Fix reference creation when custom type for documentation is provided - [@bikolya](https://github.com/bikolya).
 
 ### 0.33.0 (June 21, 2019)
 

lib/grape-swagger/endpoint.rb

@@ -178,10 +178,10 @@ def params_object(route, options, path)
       parameters = partition_params(route, options).map do |param, value|
         value = { required: false }.merge(value) if value.is_a?(Hash)
         _, value = default_type([[param, value]]).first if value == ''
-        if value[:type]
-          expose_params(value[:type])
-        elsif value[:documentation]
+        if value.dig(:documentation, :type)
           expose_params(value[:documentation][:type])
+        elsif value[:type]
+          expose_params(value[:type])
         end
         GrapeSwagger::DocMethods::ParseParams.call(param, value, path, route, @definitions)
       end

spec/swagger_v2/endpoint_versioned_path_spec.rb

@@ -52,6 +52,39 @@
         expect(subject.first['/v1/item'][:get][:tags]).to eq ['special-item']
       end
     end
+
+    context 'when parameter with a custom type is specified' do
+      let(:item) do
+        Class.new(Grape::API) do
+          Color = Struct.new(:value) do
+            def self.parse(value)
+              new(value: value)
+            end
+          end
+
+          class ColorEntity < Grape::Entity
+            expose :value
+          end
+
+          version 'v1', using: :path
+
+          resource :item do
+            params do
+              requires :root, type: Hash do
+                optional :color, type: Color, documentation: { type: ColorEntity }
+              end
+            end
+            post '/'
+          end
+        end
+      end
+
+      it 'creates a reference to the model instead of using the non-existent type' do
+        color = subject.dig(1, 'postV1Item', :properties, :root, :properties, :color)
+        expect(color).not_to eq(type: 'ColorEntity')
+        expect(color).to eq('$ref' => '#/definitions/ColorEntity')
+      end
+    end
   end
 
   context 'when mounting an API more than once', if: GrapeVersion.satisfy?('>= 1.2.0') do