Don't synchronize default branch when updating a SSH mirror

Disable the default branch update if SSH project mirrors are
being used for now, since it is affecting GitLab.com users

ee/app/services/projects/update_mirror_service.rb

@@ -63,9 +63,20 @@ module Projects
 
     # Update the default branch querying the remote to determine its HEAD
     def update_root_ref
+      # Fetch remote default branch doesn't work with SSH mirrors:
+      # https://gitlab.com/gitlab-org/gitaly/issues/1363
+      return if ssh_mirror?
+
       project.update_root_ref(::Repository::MIRROR_REMOTE)
     end
 
+    def ssh_mirror?
+      uri = Addressable::URI.parse(project.import_url)
+      uri.scheme.present? && uri.scheme == 'ssh'
+    rescue Addressable::URI::InvalidURIError
+      false
+    end
+
     def update_tags(&block)
       old_tags = repository_tags_with_target.each_with_object({}) { |tag, tags| tags[tag.name] = tag }
 

ee/changelogs/unreleased/1363-fetch-remote-default-branch-doesn-t-work-with-ssh-mirrors.yml

+---
+title: Don't synchronize default branch when updating a SSH mirror
+merge_request: 7891
+author:
+type: fixed

ee/spec/services/projects/update_mirror_service_spec.rb

@@ -209,6 +209,7 @@ describe Projects::UpdateMirrorService do
       end
     end
 
+    context 'synchronize the default branch' do
       it 'updates the default branch when HEAD has changed' do
         stub_fetch_mirror(project)
         stub_find_remote_root_ref(project, ref: 'new-branch')
@@ -223,6 +224,17 @@ describe Projects::UpdateMirrorService do
         expect { service.execute }.not_to change { project.default_branch }
       end
 
+      it 'does not update the default branch with SSH mirrors' do
+        project.update(import_url: 'ssh://git@example.com/foo/bar.git')
+
+        expect(project.repository)
+          .not_to receive(:find_remote_root_ref)
+          .with('upstream')
+
+        service.execute
+      end
+    end
+
     it "fails when the mirror user doesn't have access" do
       stub_fetch_mirror(project)
       stub_find_remote_root_ref(project)