Fix null pipeline problem

lib/gitlab/import_export/project_tree_restorer.rb

@@ -136,9 +136,18 @@ module Gitlab
         return if tree_hash[relation_key].blank?
 
         tree_array = [tree_hash[relation_key]].flatten
+        null_iid_pipelines = []
 
         # Avoid keeping a possible heavy object in memory once we are done with it
-        while relation_item = tree_array.shift
+        while relation_item = (tree_array.shift || null_iid_pipelines.shift)
+          if nil_iid_pipeline?(relation_key, relation_item) && tree_array.any?
+            # Move pipelines with NULL IIDs to the end
+            # so they don't clash with existing IIDs.
+            null_iid_pipelines << relation_item
+
+            next
+          end
+
           # The transaction at this level is less speedy than one single transaction
           # But we can't have it in the upper level or GC won't get rid of the AR objects
           # after we save the batch.
@@ -201,6 +210,10 @@ module Gitlab
       def excluded_keys_for_relation(relation)
         reader.attributes_finder.find_excluded_keys(relation)
       end
+
+      def nil_iid_pipeline?(relation_key, relation_item)
+        relation_key == 'pipelines' && relation_item['iid'].nil?
+      end
     end
   end
 end

lib/gitlab/import_export/relation_factory.rb

@@ -86,7 +86,6 @@ module Gitlab
         case @relation_name
         when :merge_request_diff_files       then setup_diff
         when :notes                          then setup_note
-        when 'Ci::Pipeline'                  then setup_pipeline
         end
 
         update_user_references
@@ -94,6 +93,8 @@ module Gitlab
         update_group_references
         remove_duplicate_assignees
 
+        setup_pipeline if @relation_name == 'Ci::Pipeline'
+
         reset_tokens!
         remove_encrypted_attributes!
       end

spec/lib/gitlab/import_export/project.json

@@ -6143,7 +6143,7 @@
       "id": 36,
       "project_id": 5,
       "ref": "master",
-      "sha": "be93687618e4b132087f430a4d8fc3a609c9b77c",
+      "sha": "sha-notes",
       "before_sha": null,
       "push_data": null,
       "created_at": "2016-03-22T15:20:35.755Z",
@@ -6353,6 +6353,7 @@
     },
     {
       "id": 38,
+      "iid": 1,
       "project_id": 5,
       "ref": "master",
       "sha": "5f923865dde3436854e9ceb9cdb7815618d4e849",

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -59,7 +59,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
       end
 
       it 'creates a valid pipeline note' do
-        expect(Ci::Pipeline.first.notes).not_to be_empty
+        expect(Ci::Pipeline.find_by_sha('sha-notes').notes).not_to be_empty
       end
 
       it 'restores pipelines with missing ref' do