Import pull requests from GitHub where the target branch was removed

lib/gitlab/github_import/importer.rb

@@ -75,10 +75,11 @@ module Gitlab
                               .map { |raw| PullRequestFormatter.new(project, raw) }
                               .reject(&:cross_project?)
 
-        source_branches_removed = pull_requests.reject(&:source_branch_exists?)
-        source_branches_removed.each do |pull_request|
-          client.create_ref(repo, "refs/heads/#{pull_request.source_branch}", pull_request.source_sha)
-        end
+        source_branches_removed = pull_requests.reject(&:source_branch_exists?).map { |pr| [pr.source_branch, pr.source_sha] }
+        target_branches_removed = pull_requests.reject(&:target_branch_exists?).map { |pr| [pr.target_branch, pr.target_sha] }
+        branches_removed = source_branches_removed | target_branches_removed
+
+        create_refs(branches_removed)
 
         project.repository.fetch_ref(repo_url, '+refs/heads/*', 'refs/heads/*')
 
@@ -92,15 +93,25 @@ module Gitlab
           end
         end
 
-        source_branches_removed.each do |pull_request|
-          client.delete_ref(repo, "heads/#{pull_request.source_branch}")
-        end
+        delete_refs(branches_removed)
 
         true
       rescue ActiveRecord::RecordInvalid => e
         raise Projects::ImportService::Error, e.message
       end
 
+      def create_refs(branches)
+        branches.each do |branch|
+          client.create_ref(repo, "refs/heads/#{branch.first}", branch.last)
+        end
+      end
+
+      def delete_refs(branches)
+        branches.each do |branch|
+          client.delete_ref(repo, "heads/#{branch.first}")
+        end
+      end
+
       def apply_labels(number, issuable)
         issue = client.issue(project.import_source, number)
 

lib/gitlab/github_import/pull_request_formatter.rb

@@ -9,7 +9,7 @@ module Gitlab
           source_project: source_project,
           source_branch: source_branch,
           target_project: target_project,
-          target_branch: target_branch.name,
+          target_branch: target_branch,
           state: state,
           milestone: milestone,
           author_id: author_id,
@@ -43,6 +43,18 @@ module Gitlab
         raw_data.head.sha
       end
 
+      def target_branch_exists?
+        target_project.repository.branch_names.include?(target_branch)
+      end
+
+      def target_branch
+        raw_data.base.ref
+      end
+
+      def target_sha
+        raw_data.base.sha
+      end
+
       private
 
       def assigned?
@@ -93,10 +105,6 @@ module Gitlab
         raw_data.base.repo
       end
 
-      def target_branch
-        target_project.repository.find_branch(raw_data.base.ref)
-      end
-
       def state
         @state ||= case true
                    when raw_data.state == 'closed' && raw_data.merged_at.present?