Prevent re-adding same transformers to the view all the time

lib/blueprinter/view_collection.rb

@@ -36,7 +36,7 @@ def fields_for(view_name)
 
     def transformers(view_name)
       included_transformers = gather_transformers_from_included_views(view_name).reverse
-      all_transformers = views[:default].view_transformers.concat(included_transformers).uniq
+      all_transformers = [*views[:default].view_transformers, *included_transformers].uniq
       all_transformers.empty? ? Blueprinter.configuration.default_transformers : all_transformers
     end
 
@@ -94,11 +94,12 @@ def add_to_ordered_fields(ordered_fields, definition, fields, view_name_filter =
 
     def gather_transformers_from_included_views(view_name)
       current_view = views[view_name]
-      current_view.included_view_names.flat_map do |included_view_name|
+      already_included_transformers = current_view.included_view_names.flat_map do |included_view_name|
         next [] if view_name == included_view_name
 
         gather_transformers_from_included_views(included_view_name)
-      end.concat(current_view.view_transformers)
+      end
+      [*already_included_transformers, *current_view.view_transformers].uniq
     end
   end
 end

spec/benchmarks/ips_test.rb

@@ -9,8 +9,19 @@ class Blueprinter::IPSTest < Minitest::Test
 
   def setup
     @blueprinter = Class.new(Blueprinter::Base) do
+      transformer = Class.new(Blueprinter::Transformer) do
+        define_method :transform do |result_hash, _obj, _options|
+          {
+            foo: :bar,
+            **result_hash
+          }
+        end
+      end
+
       field :id
       field :name
+
+      transform transformer
     end
     @prepared_objects = 10.times.map {|i| OpenStruct.new(id: i, name: "obj #{i}")}
   end

spec/units/view_collection_spec.rb

@@ -91,6 +91,12 @@
       it 'should return both the view transformer and default transformers for the view' do
         expect(view_collection.transformers(:view)).to eq([default_transformer, transformer])
       end
+
+      it 'should not alter view transformers of the view on subsequent fetches' do
+        view_collection.transformers(:default)
+        expect { view_collection.transformers(:default) }
+          .not_to change(default_view.view_transformers, :count)
+      end
     end
 
     context 'include view transformer' do