checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">

<!--
  The style the generator writes and the hand-written half is held to.

  Checkstyle rather than a rewriting formatter, and for the same reason RuboCop guards the Ruby
  client: this check validates, it never corrects. A job that rewrote what it was checking would
  report success on source nobody wrote, and the emitter — not a pass after it — stays the one place
  that decides what the generated half looks like.

  Every rule below is one the emitter satisfies as it emits: the margin it folds comments and calls
  at, the indentation it writes, the import block it sorts, and the documentation it puts on every
  public type.
-->
<module name="Checker">
  <property name="charset" value="UTF-8"/>
  <property name="severity" value="error"/>
  <property name="fileExtensions" value="java"/>

  <!-- Nothing is written past the margin the emitter folds at. -->
  <module name="LineLength">
    <property name="max" value="120"/>
    <property name="ignorePattern" value="^\s*(//|\*) *https?://"/>
  </module>

  <module name="NewlineAtEndOfFile"/>
  <module name="FileTabCharacter"/>
  <module name="RegexpSingleline">
    <property name="format" value="\s+$"/>
    <property name="message" value="a line ends in whitespace"/>
  </module>

  <module name="TreeWalker">
    <!-- Imports: one sorted block, nothing unused, nothing wholesale. -->
    <module name="AvoidStarImport"/>
    <module name="RedundantImport"/>
    <module name="UnusedImports"/>
    <module name="CustomImportOrder">
      <!--
        Two groups: what a file imports statically, then what it imports as a type, each sorted the
        way plain string ordering sorts it. The generated half never imports statically, so its
        block is one group and the emitter sorts it as it writes it.
      -->
      <property name="customImportOrderRules" value="STATIC###THIRD_PARTY_PACKAGE"/>
      <property name="sortImportsInGroupAlphabetically" value="true"/>
      <property name="separateLineBetweenGroups" value="true"/>
    </module>

    <!-- Naming, as every Java reader expects it. -->
    <module name="PackageName"/>
    <module name="TypeName"/>
    <module name="MethodName"/>
    <module name="MemberName"/>
    <module name="ParameterName"/>
    <module name="LocalVariableName"/>
    <module name="ConstantName"/>

    <!-- Layout the emitter writes and a hand edit has to keep. -->
    <module name="LeftCurly"/>
    <module name="RightCurly"/>
    <module name="NeedBraces"/>
    <module name="WhitespaceAfter"/>
    <module name="NoWhitespaceBefore"/>
    <module name="GenericWhitespace"/>
    <module name="MethodParamPad"/>
    <module name="ParenPad"/>
    <module name="EmptyLineSeparator">
      <property name="allowNoEmptyLineBetweenFields" value="true"/>
      <property name="allowMultipleEmptyLines" value="false"/>
      <property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
      <property name="tokens"
                value="PACKAGE_DEF, IMPORT, CLASS_DEF, ENUM_DEF, INTERFACE_DEF, RECORD_DEF, CTOR_DEF, METHOD_DEF"/>
    </module>

    <!-- Every public type says what it is. -->
    <module name="MissingJavadocType">
      <property name="scope" value="public"/>
    </module>

    <!-- Defects the compiler does not report. -->
    <module name="EqualsHashCode"/>
    <module name="StringLiteralEquality"/>
    <module name="FallThrough"/>
    <!--
      `MissingSwitchDefault` is deliberately absent. The generated match over the problem catalogue
      is a switch expression over a closed enumeration, and its exhaustiveness is what turns a
      problem the API grows into a compilation failure. A default branch would answer for the new
      value instead, and the compiler would stop mentioning it.
    -->
    <module name="ModifierOrder"/>
    <module name="UpperEll"/>
    <module name="ArrayTypeStyle"/>
    <module name="OneTopLevelClass"/>
    <module name="OuterTypeFilename"/>
  </module>
</module>