refactor code once again to fix IID issues

lib/gitlab/import_export/group_project_finder.rb

@@ -14,7 +14,7 @@ module Gitlab
       end
 
       def initialize(klass, attributes)
-        @klass = klass
+        @klass = klass < Label ? Label : klass
         @attributes = attributes
         @group = @attributes[:group]
         @project = @attributes[:project]
@@ -33,7 +33,7 @@ module Gitlab
       def where_clause
         return { project_id: @project.id } unless milestone? || label?
 
-        @attributes.slice(:title).map do |key, value|
+        @attributes.slice('title').map do |key, value|
           project_clause = table[key].eq(value).and(table[:project_id].eq(@project.id))
 
           if @group
@@ -51,9 +51,9 @@ module Gitlab
       def project_attributes
         @attributes.except(:group).tap do |atts|
           if label?
-            atts['type'] = 'ProjectLabel'
+            atts['type'] = 'ProjectLabel' # Always create project labels
           elsif milestone?
-            if atts['group_id']
+            if atts['group_id'] # Transform new group milestones into project ones
               atts['iid'] = nil
               atts.delete('group_id')
             else
@@ -64,13 +64,18 @@ module Gitlab
       end
 
       def label?
-        @klass == Label || @klass < Label
+        @klass == Label
       end
 
       def milestone?
         @klass == Milestone
       end
 
+      # If an existing group milesone used the IIID
+      # claim the IID back and set the group milestone to use one available
+      # This is neccessary to fix situations like the following:
+      #  - Importing into a user namespace project with exported group milestones
+      #    where the IID of the Group milestone could conflict with a project one.
       def claim_iid
         group_milestone = @project.milestones.find_by(iid: @attributes['iid'])
 

lib/gitlab/import_export/relation_factory.rb

@@ -80,7 +80,6 @@ module Gitlab
         case @relation_name
         when :merge_request_diff_files       then setup_diff
         when :notes                          then setup_note
-        when *(EXISTING_OBJECT_CHECK - [:project_feature])  then setup_project_group
         when 'Ci::Pipeline'                  then setup_pipeline
         else
           @relation_hash['project_id'] = @project.id
@@ -166,12 +165,6 @@ module Gitlab
         @relation_hash['target_project_id'] && @relation_hash['target_project_id'] == @relation_hash['source_project_id']
       end
 
-      def setup_project_group
-        @relation_hash['project_id'] = @project.id
-        @relation_hash['group_id'] = @project.group&.id
-        @relation_hash.delete('type')
-      end
-
       def reset_tokens!
         return unless Gitlab::ImportExport.reset_tokens? && TOKEN_RESET_MODELS.include?(@relation_name.to_s)
 
@@ -266,27 +259,14 @@ module Gitlab
       end
 
       def find_or_create_object!
-        # Can't use IDs as validation exists calilng `.group` or `.project`
+        # Can't use IDs as validation exists calling `group` or `project` attributes
         finder_hash = parsed_relation_hash.tap do |hash|
           hash[:group] = @project.group if relation_class.attribute_method?('group_id')
           hash[:project] = @project
-          hash[:title] = parsed_relation_hash['title'] if parsed_relation_hash['title']
           hash.delete('project_id')
         end
 
-        if label?
-          GroupProjectFinder.find_or_new(Label, finder_hash)
-        else
-          GroupProjectFinder.find_or_create(relation_class, finder_hash)
-        end
-      end
-
-      def label?
-        @relation_name.to_s.include?('label')
-      end
-
-      def milestone?
-        @relation_name.to_s.include?('milestone')
+        GroupProjectFinder.find_or_create(relation_class, finder_hash)
       end
     end
   end

spec/lib/gitlab/import_export/project.light.json

@@ -67,7 +67,7 @@
       "milestone": {
         "id": 1,
         "title": "A milestone",
-        "project_id": 8,
+        "group_id": 8,
         "description": "Project-level milestone",
         "due_date": null,
         "created_at": "2016-06-14T15:02:04.415Z",