tools/checkstyle/checkstyle-forbid-gpl.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd">
<!-- Copyright (C) 2019 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
-->
<!-- Ensures that files checked with this checker do not contain GPL
     license text. This is done by searching for license name preceded by
     comment asterisk:
     " * ... GNU General Public License ..."
-->

<module name="Checker">
  <property name="fileExtensions" value="java"/>

  <module name="RegexpSingleline">
    <property name="severity" value="error"/>
    <property name="format" value="^\W+\*.*GNU General Public License.*$" />
    <property name="message" value="files MUST NOT have GPL license"/>
  </module>

</module>