openproject/app/views/projects/form/attributes/_parent_id.html.erb

<%#-- copyright
OpenProject is an open source project management software.
Copyright (C) 2012-2020 the OpenProject GmbH

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License version 3.

OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
Copyright (C) 2006-2017 Jean-Philippe Lang
Copyright (C) 2010-2013 the ChiliProject Team

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

See docs/COPYRIGHT.rdoc for more details.

++#%>

<%
  project = form.object
  allowed_parents = allowed_parent_projects(project).to_a
%>

<% unless allowed_parents.empty? %>
  <div class="form--field">
    <%= form.select :parent_id,
                    project_tree_options_for_select(allowed_parents,
                                                    selected: project.parent),
                    include_blank: true,
                    container_class: '-wide' %>
  </div>
<% end %>