dev/checkstyle.xml

<?xml version="1.0" encoding="UTF-8"?>
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      Licensed to the Apache Software Foundation (ASF) under one or more
      contributor license agreements.  See the NOTICE file distributed with
      this work for additional information regarding copyright ownership.
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      (the "License"); you may not use this file except in compliance with
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      distributed under the License is distributed on an "AS IS" BASIS,
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  -->
<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">

<!--
  Minimal Checkstyle configuration. Formatting is owned by Spotless
  (palantir-java-format); this file only enforces structural rules that a
  formatter cannot express. Add rules deliberately and sparingly.
-->
<module name="Checker">
  <property name="charset" value="UTF-8"/>
  <property name="severity" value="error"/>

  <module name="TreeWalker">
    <!--
      Tests must use JUnit 5 (Jupiter). Reject JUnit 3 (junit.framework)
      and JUnit 4 (org.junit.*) imports while allowing org.junit.jupiter
      and org.junit.platform.
    -->
    <module name="IllegalImport">
      <property name="regexp" value="true"/>
      <!--
        Checkstyle appends "\..*" to each package pattern, so entries must
        not end with a trailing dot.
      -->
      <property name="illegalPkgs"
                value="^junit, ^org\.junit(?!\.(jupiter|platform)\.)"/>
      <message key="import.illegal"
               value="JUnit 3/4 is banned; use JUnit 5 (org.junit.jupiter) instead."/>
    </module>
  </module>
</module>