Extract MR's widget into a separate endpoint

This commits extracts /merge_requests/1.json?serializer=widget
Into a separate /merge_requests/1/widget.json endpoint
This will allow to use caching for this request

3 files changed, 29 insertions, 6 deletions

diff --git a/app/controllers/projects/merge_requests/application_controller.rb b/app/controllers/projects/merge_requests/application_controller.rb
index f2a6268b3e9..dcc272aecff 100644
--- a/app/controllers/projects/merge_requests/application_controller.rb
+++ b/app/controllers/projects/merge_requests/application_controller.rb
@@ -51,4 +51,11 @@ class Projects::MergeRequests::ApplicationController < Projects::ApplicationCont
         Ci::Pipeline.none
       end
   end
+
+  def close_merge_request_if_no_source_project
+    return if @merge_request.source_project
+    return unless @merge_request.open?
+
+    @merge_request.close
+  end
 end
diff --git a/app/controllers/projects/merge_requests/content_controller.rb b/app/controllers/projects/merge_requests/content_controller.rb
new file mode 100644
index 00000000000..6e026b83ee3
--- /dev/null
+++ b/app/controllers/projects/merge_requests/content_controller.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class Projects::MergeRequests::ContentController < Projects::MergeRequests::ApplicationController
+  # @merge_request.check_mergeability is not executed here since
+  # widget serializer calls it via mergeable? method
+  # but we might want to call @merge_request.check_mergeability
+  # for other types of serialization
+
+  before_action :close_merge_request_if_no_source_project
+  around_action :allow_gitaly_ref_name_caching
+
+  def widget
+    respond_to do |format|
+      format.json do
+        Gitlab::PollingInterval.set_header(response, interval: 10_000)
+
+        serializer = MergeRequestSerializer.new(current_user: current_user, project: merge_request.project)
+        render json: serializer.represent(merge_request, serializer: 'widget')
+      end
+    end
+  end
+end
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index fc37ce1dbc4..7ee8e0ea8f8 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -235,12 +235,6 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     params[:auto_merge_strategy].present? || params[:merge_when_pipeline_succeeds].present?
   end
 
-  def close_merge_request_if_no_source_project
-    if !@merge_request.source_project && @merge_request.open?
-      @merge_request.close
-    end
-  end
-
   private
 
   def ci_environments_status_on_merge_result?