Simplify implementation of entity serializers

app/serializers/base_serializer.rb

 class BaseSerializer
   def initialize(parameters = {})
-    @entity = self.class.entity_class
     @request = EntityRequest.new(parameters)
-    @opts = { request: @request }
-  end
-
-  def set(parameters)
-    @request.merge!(parameters)
-    self
   end
 
   def represent(resource, opts = {})
-    @entity.represent(resource, @opts.reverse_merge(opts))
+    self.class.entity_class
+      .represent(resource, opts.merge(request: @request))
   end
 
   def self.entity(entity_class)

app/serializers/build_entity.rb

@@ -19,6 +19,6 @@ class BuildEntity < Grape::Entity
   private
 
   def url_to(route, build)
-    @urls.send("#{route}_url", build.project.namespace, build.project, build)
+    send("#{route}_url", build.project.namespace, build.project, build)
   end
 end

app/serializers/commit_entity.rb

@@ -4,9 +4,9 @@ class CommitEntity < API::Entities::RepoCommit
   expose :author, using: UserEntity
 
   expose :commit_url do |commit|
-    @urls.namespace_project_tree_url(
-      @request.project.namespace,
-      @request.project,
+    namespace_project_tree_url(
+      request.project.namespace,
+      request.project,
       id: commit.id)
   end
 end

app/serializers/deployment_entity.rb

@@ -11,7 +11,7 @@ class DeploymentEntity < Grape::Entity
     end
 
     expose :ref_url do |deployment|
-      @urls.namespace_project_tree_url(
+      namespace_project_tree_url(
         deployment.project.namespace,
         deployment.project,
         id: deployment.ref)

app/serializers/entity_request.rb

@@ -5,10 +5,6 @@ class EntityRequest
   # that is present in the controller (see  #20045).
   #
   def initialize(parameters)
-    merge!(parameters)
-  end
-
-  def merge!(parameters)
     parameters.each do |key, value|
       define_singleton_method(key) { value }
     end

app/serializers/environment_entity.rb

@@ -10,7 +10,7 @@ class EnvironmentEntity < Grape::Entity
   expose :stoppable?
 
   expose :environment_url do |environment|
-    @urls.namespace_project_environment_url(
+    namespace_project_environment_url(
       environment.project.namespace,
       environment.project,
       environment)

app/serializers/request_aware_entity.rb

 module RequestAwareEntity
-  attr_reader :request
+  extend ActiveSupport::Concern
 
-  def initialize(object, options = {})
-    super(object, options)
+  included do
+    include Gitlab::Routing.url_helpers
+  end
 
-    @request = options.fetch(:request)
-    @urls = Gitlab::Routing.url_helpers
+  def request
+    @options.fetch(:request)
   end
 end

spec/serializers/entity_request_spec.rb

@@ -15,12 +15,4 @@ describe EntityRequest do
       expect { subject.some_method }.to raise_error NoMethodError
     end
   end
-
-  describe '#merge!' do
-    before { subject.merge!(build: 'some build') }
-
-    it 'appends parameters' do
-      expect(subject.build).to eq 'some build'
-    end
-  end
 end