Import threaded discussions in diffs

lib/gitlab/bitbucket_server_import/importer.rb

@@ -135,7 +135,23 @@ module Gitlab
         end
 
         inline_comments.each do |comment|
-          begin
+          parent = build_diff_note(merge_request, comment, line_code_map)
+
+          next unless parent&.persisted?
+
+          comment.comments.each do |reply|
+            attributes = pull_request_comment_attributes(reply)
+            attributes.merge!(
+              position: build_position(merge_request, comment),
+              line_code: line_code_map.fetch(reply.id)
+              discussion_id: parent.discussion_id,
+              type: 'DiffNote')
+            merge_request.notes.create!(attributes)
+          end
+        end
+      end
+
+      def build_diff_note(merge_request, comment, line_code_map)
         attributes = pull_request_comment_attributes(comment)
         attributes.merge!(
           position: build_position(merge_request, comment),
@@ -145,8 +161,7 @@ module Gitlab
         merge_request.notes.create!(attributes)
       rescue StandardError => e
         errors << { type: :pull_request, id: comment.id, errors: e.message }
-          end
-        end
+        nil
       end
 
       def build_position(merge_request, pr_comment)