checkstyle.xml

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

<!--
    Based on google_checks.xml
    (https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml)
    with a few tweaks by Will Molloy (https://willmolloy.com/).

    Note this assumes spotless (with googleJavaFormat()) is used in conjunction with checkstyle.
    Therefore some rules (e.g. LineLength, Indentation) are disabled as they conflict with spotless.
 -->

<module name="Checker">
  <property name="charset" value="UTF-8"/>

  <property name="severity" value="warning"/>

  <property name="fileExtensions" value="java, properties, xml"/>
  <!-- Excludes all 'module-info.java' files              -->
  <!-- See https://checkstyle.org/config_filefilters.html -->
  <module name="BeforeExecutionExclusionFileFilter">
    <property name="fileNamePattern" value="module\-info\.java$"/>
  </module>
  <!-- https://checkstyle.org/config_filters.html#SuppressionFilter -->
  <module name="SuppressionFilter">
    <property name="file" value="${suppressionFile}"/>
    <property name="optional" value="false"/>
  </module>

  <!-- Checks for whitespace                               -->
  <!-- See http://checkstyle.org/config_whitespace.html -->
  <module name="FileTabCharacter">
    <property name="eachLine" value="true"/>
  </module>

  <!-- LineLength is covered by spotless, want to allow things like large strings and javadoc links -->
  <!--    <module name="LineLength">-->
  <!--        <property name="fileExtensions" value="java"/>-->
  <!--        <property name="max" value="100"/>-->
  <!--        <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>-->
  <!--    </module>-->

  <module name="TreeWalker">
    <module name="OuterTypeFilename"/>
    <module name="IllegalTokenText">
      <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>
      <property name="format"
                value="\\u00(09|0(a|A)|0(c|C)|0(d|D)|22|27|5(C|c))|\\(0(10|11|12|14|15|42|47)|134)"/>
      <property name="message"
                value="Consider using special escape sequence instead of octal value or Unicode escaped value."/>
    </module>
    <module name="AvoidEscapedUnicodeCharacters">
      <property name="allowEscapesForControlCharacters" value="true"/>
      <property name="allowByTailComment" value="true"/>
      <property name="allowNonPrintableEscapes" value="true"/>
    </module>
    <module name="AvoidStarImport"/>
    <module name="OneTopLevelClass"/>
    <module name="NoLineWrap">
      <property name="tokens" value="PACKAGE_DEF, IMPORT, STATIC_IMPORT"/>
    </module>
    <module name="EmptyBlock">
      <property name="option" value="TEXT"/>
      <property name="tokens"
                value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
    </module>
    <module name="NeedBraces">
      <property name="tokens"
                value="LITERAL_DO, LITERAL_ELSE, LITERAL_FOR, LITERAL_IF, LITERAL_WHILE"/>
    </module>
    <module name="LeftCurly">
      <property name="tokens"
                value="ANNOTATION_DEF, CLASS_DEF, CTOR_DEF, ENUM_CONSTANT_DEF, ENUM_DEF,
                    INTERFACE_DEF, LAMBDA, LITERAL_CASE, LITERAL_CATCH, LITERAL_DEFAULT,
                    LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF,
                    LITERAL_SWITCH, LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, METHOD_DEF,
                    OBJBLOCK, STATIC_INIT"/>
    </module>
    <module name="RightCurly">
      <property name="id" value="RightCurlySame"/>
      <property name="tokens"
                value="LITERAL_TRY, LITERAL_CATCH, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE,
                    LITERAL_DO"/>
    </module>
    <module name="RightCurly">
      <property name="id" value="RightCurlyAlone"/>
      <property name="option" value="alone"/>
      <property name="tokens"
                value="CLASS_DEF, METHOD_DEF, CTOR_DEF, LITERAL_FOR, LITERAL_WHILE, STATIC_INIT,
                    INSTANCE_INIT, ANNOTATION_DEF, ENUM_DEF"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <!-- suppresion is required till https://github.com/checkstyle/checkstyle/issues/7541 -->
      <property name="id" value="RightCurlyAlone"/>
      <property name="query" value="//RCURLY[parent::SLIST[count(./*)=1]
                                                 or preceding-sibling::*[last()][self::LCURLY]]"/>
    </module>
    <module name="WhitespaceAfter">
      <property name="tokens"
                value="COMMA, SEMI, TYPECAST, LITERAL_IF, LITERAL_ELSE,
                    LITERAL_WHILE, LITERAL_DO, LITERAL_FOR, DO_WHILE"/>
    </module>
    <module name="WhitespaceAround">
      <property name="allowEmptyConstructors" value="true"/>
      <property name="allowEmptyLambdas" value="true"/>
      <property name="allowEmptyMethods" value="true"/>
      <property name="allowEmptyTypes" value="true"/>
      <property name="allowEmptyLoops" value="true"/>
      <property name="tokens"
                value="ASSIGN, BAND, BAND_ASSIGN, BOR, BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR,
                    BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN, DO_WHILE, EQUAL, GE, GT, LAMBDA, LAND,
                    LCURLY, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY,
                    LITERAL_FOR, LITERAL_IF, LITERAL_RETURN, LITERAL_SWITCH, LITERAL_SYNCHRONIZED,
                     LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS, MINUS_ASSIGN, MOD, MOD_ASSIGN,
                     NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION, RCURLY, SL, SLIST, SL_ASSIGN, SR,
                     SR_ASSIGN, STAR, STAR_ASSIGN, LITERAL_ASSERT, TYPE_EXTENSION_AND"/>
      <message key="ws.notFollowed"
               value="WhitespaceAround: ''{0}'' is not followed by whitespace. Empty blocks may only be represented as '{}' when not part of a multi-block statement (4.1.3)"/>
      <message key="ws.notPreceded"
               value="WhitespaceAround: ''{0}'' is not preceded with whitespace."/>
    </module>
    <module name="OneStatementPerLine"/>
    <module name="MultipleVariableDeclarations"/>
    <module name="ArrayTypeStyle"/>
    <module name="MissingSwitchDefault"/>
    <module name="FallThrough"/>
    <module name="UpperEll"/>
    <module name="ModifierOrder"/>
    <module name="EmptyLineSeparator">
      <property name="tokens"
                value="PACKAGE_DEF, IMPORT, STATIC_IMPORT, CLASS_DEF, INTERFACE_DEF, ENUM_DEF,
                    STATIC_INIT, INSTANCE_INIT, METHOD_DEF, CTOR_DEF, VARIABLE_DEF"/>
      <property name="allowNoEmptyLineBetweenFields" value="true"/>
    </module>
    <module name="SeparatorWrap">
      <property name="id" value="SeparatorWrapDot"/>
      <property name="tokens" value="DOT"/>
      <property name="option" value="nl"/>
    </module>
    <module name="SeparatorWrap">
      <property name="id" value="SeparatorWrapComma"/>
      <property name="tokens" value="COMMA"/>
      <property name="option" value="EOL"/>
    </module>
    <module name="SeparatorWrap">
      <!-- ELLIPSIS is EOL until https://github.com/google/styleguide/issues/258 -->
      <property name="id" value="SeparatorWrapEllipsis"/>
      <property name="tokens" value="ELLIPSIS"/>
      <property name="option" value="EOL"/>
    </module>
    <module name="SeparatorWrap">
      <!-- ARRAY_DECLARATOR is EOL until https://github.com/google/styleguide/issues/259 -->
      <property name="id" value="SeparatorWrapArrayDeclarator"/>
      <property name="tokens" value="ARRAY_DECLARATOR"/>
      <property name="option" value="EOL"/>
    </module>
    <module name="SeparatorWrap">
      <property name="id" value="SeparatorWrapMethodRef"/>
      <property name="tokens" value="METHOD_REF"/>
      <property name="option" value="nl"/>
    </module>
    <module name="PackageName">
      <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]*)*$"/>
      <message key="name.invalidPattern"
               value="Package name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="TypeName">
      <property name="tokens" value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, ANNOTATION_DEF"/>
      <message key="name.invalidPattern"
               value="Type name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="MemberName">
      <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
      <message key="name.invalidPattern"
               value="Member name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="ParameterName">
      <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
      <message key="name.invalidPattern"
               value="Parameter name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="LambdaParameterName">
      <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
      <message key="name.invalidPattern"
               value="Lambda parameter name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="CatchParameterName">
      <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
      <message key="name.invalidPattern"
               value="Catch parameter name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="LocalVariableName">
      <property name="format" value="^[a-z][a-zA-Z0-9]*$"/>
      <message key="name.invalidPattern"
               value="Local variable name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="ClassTypeParameterName">
      <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
      <message key="name.invalidPattern"
               value="Class type name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="MethodTypeParameterName">
      <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
      <message key="name.invalidPattern"
               value="Method type name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="InterfaceTypeParameterName">
      <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
      <message key="name.invalidPattern"
               value="Interface type name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="NoFinalizer"/>
    <module name="GenericWhitespace">
      <message key="ws.followed"
               value="GenericWhitespace ''{0}'' is followed by whitespace."/>
      <message key="ws.preceded"
               value="GenericWhitespace ''{0}'' is preceded with whitespace."/>
      <message key="ws.illegalFollow"
               value="GenericWhitespace ''{0}'' should followed by whitespace."/>
      <message key="ws.notPreceded"
               value="GenericWhitespace ''{0}'' is not preceded with whitespace."/>
    </module>
    <!-- Conflicts with spotless TODO this is strange as both are Google style? -->
    <!--        <module name="Indentation">-->
    <!--            <property name="basicOffset" value="2"/>-->
    <!--            <property name="braceAdjustment" value="0"/>-->
    <!--            <property name="caseIndent" value="2"/>-->
    <!--            <property name="throwsIndent" value="4"/>-->
    <!--            <property name="lineWrappingIndentation" value="4"/>-->
    <!--            <property name="arrayInitIndent" value="2"/>-->
    <!--        </module>-->
    <module name="AbbreviationAsWordInName">
      <property name="ignoreFinal" value="false"/>
      <property name="allowedAbbreviationLength" value="1"/>
      <property name="tokens"
                value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, ANNOTATION_DEF, ANNOTATION_FIELD_DEF,
                    PARAMETER_DEF, VARIABLE_DEF, METHOD_DEF"/>
    </module>
    <module name="OverloadMethodsDeclarationOrder"/>
    <!-- Personally disagree with this one -->
    <!--        <module name="VariableDeclarationUsageDistance"/>-->
    <module name="CustomImportOrder">
      <property name="sortImportsInGroupAlphabetically" value="true"/>
      <property name="separateLineBetweenGroups" value="true"/>
      <property name="customImportOrderRules" value="STATIC###THIRD_PARTY_PACKAGE"/>
      <property name="tokens" value="IMPORT, STATIC_IMPORT, PACKAGE_DEF"/>
    </module>
    <module name="MethodParamPad">
      <property name="tokens"
                value="CTOR_DEF, LITERAL_NEW, METHOD_CALL, METHOD_DEF,
                    SUPER_CTOR_CALL, ENUM_CONSTANT_DEF"/>
    </module>
    <module name="NoWhitespaceBefore">
      <property name="tokens"
                value="COMMA, SEMI, POST_INC, POST_DEC, DOT,
                    LABELED_STAT, METHOD_REF"/>
      <property name="allowLineBreaks" value="true"/>
    </module>
    <module name="ParenPad">
      <property name="tokens"
                value="ANNOTATION, ANNOTATION_FIELD_DEF, CTOR_CALL, CTOR_DEF, DOT, ENUM_CONSTANT_DEF,
                    EXPR, LITERAL_CATCH, LITERAL_DO, LITERAL_FOR, LITERAL_IF, LITERAL_NEW,
                    LITERAL_SWITCH, LITERAL_SYNCHRONIZED, LITERAL_WHILE, METHOD_CALL,
                    METHOD_DEF, QUESTION, RESOURCE_SPECIFICATION, SUPER_CTOR_CALL, LAMBDA"/>
    </module>
    <module name="OperatorWrap">
      <property name="option" value="NL"/>
      <property name="tokens"
                value="BAND, BOR, BSR, BXOR, DIV, EQUAL, GE, GT, LAND, LE, LITERAL_INSTANCEOF, LOR,
                    LT, MINUS, MOD, NOT_EQUAL, PLUS, QUESTION, SL, SR, STAR, METHOD_REF "/>
    </module>
    <module name="AnnotationLocation">
      <property name="id" value="AnnotationLocationMostCases"/>
      <property name="tokens"
                value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF"/>
    </module>
    <module name="AnnotationLocation">
      <property name="id" value="AnnotationLocationVariables"/>
      <property name="tokens" value="VARIABLE_DEF"/>
      <property name="allowSamelineMultipleAnnotations" value="true"/>
    </module>
    <module name="NonEmptyAtclauseDescription"/>
    <module name="InvalidJavadocPosition"/>
    <module name="JavadocTagContinuationIndentation"/>
    <module name="SummaryJavadoc">
      <property name="forbiddenSummaryFragments"
                value="^@return the *|^This method returns |^A [{]@code [a-zA-Z0-9]+[}]( is a )"/>
    </module>
    <module name="JavadocParagraph"/>
    <module name="AtclauseOrder">
      <property name="tagOrder" value="@param, @return, @throws, @deprecated"/>
      <property name="target"
                value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF, VARIABLE_DEF"/>
    </module>
    <module name="JavadocMethod">
      <property name="accessModifiers" value="public"/>
      <property name="allowMissingParamTags" value="true"/>
      <property name="allowMissingReturnTag" value="true"/>
      <property name="allowedAnnotations" value="Override, Test"/>
      <property name="tokens" value="METHOD_DEF, CTOR_DEF, ANNOTATION_FIELD_DEF"/>
    </module>
    <module name="MissingJavadocMethod">
      <property name="scope" value="public"/>
      <property name="minLineCount" value="2"/>
      <property name="allowedAnnotations" value="Override, Test"/>
      <property name="tokens" value="METHOD_DEF, ANNOTATION_FIELD_DEF"/>
    </module>
    <module name="MethodName">
      <property name="format" value="^[a-z][a-z0-9][a-zA-Z0-9_]*$"/>
      <message key="name.invalidPattern"
               value="Method name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="SingleLineJavadoc">
      <property name="ignoreInlineTags" value="true"/>
    </module>
    <module name="EmptyCatchBlock">
      <property name="exceptionVariableName" value="expected"/>
    </module>
    <module name="CommentsIndentation">
      <property name="tokens" value="SINGLE_LINE_COMMENT, BLOCK_COMMENT_BEGIN"/>
    </module>

    <!-- added checks -->
    <module name="OneTopLevelClass"/>
    <module name="FinalClass"/>
    <module name="HideUtilityClassConstructor"/>
    <module name="RedundantImport"/>
    <module name="UnusedImports"/>
    <module name="RedundantModifier"/>
    <module name="MissingDeprecated"/>
    <module name="InnerAssignment"/>
    <module name="ConstantName">
      <property name="format"
                value="^log?$|^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$"/>
    </module>
    <module name="EqualsHashCode"/>
    <module name="ExplicitInitialization"/>
    <module name="AvoidNestedBlocks"/>
    <module name="StaticVariableName"/>
    <module name="MissingJavadocType">
      <property name="scope" value="package"/>
    </module>
    <module name="JavadocType">
      <property name="authorFormat" value=".+"/>
    </module>

    <!-- Regexp for test files (note assumes checkstyle runs on test files!) -->
    <!-- Ensure only JUnit 5 is used -->
    <module name="RegexpSinglelineJava">
      <property name="format" value="junit\.(?!jupiter)"/>
      <property name="ignoreComments" value="true"/>
      <property name="message" value="Use JUnit 5."/>
    </module>
    <!-- Ensure only Google Truth is used. Exception made for JUnit 5 assertThrows, assertAll, and fail.
    TODO remove assertThrows exclusion when Truth supports it
    -->
    <module name="RegexpSinglelineJava">
      <property name="format"
                value="import.*(?&lt;!com\.google\.common\.truth\.Truth8?\.)(A|a)ssert(?!.*(Throws|DoesNotThrow|All|fail))"/>
      <property name="ignoreComments" value="true"/>
      <property name="message" value="Use com.google.truth.Truth assertions."/>
    </module>
    <module name="RegexpSinglelineJava">
      <property name="format"
                value="(?&lt;!import static.*)(Truth|Assertions|Mockito|ArgumentMatchers)(?!.*(Extension|Settings))"/>
      <property name="ignoreComments" value="true"/>
      <property name="message" value="Use a static import."/>
    </module>

    <!-- Regexp for JavaDoc -->
    <!-- Ensure links in Javadocs are tagged correctly -->
    <module name="RegexpSinglelineJava">
      <property name="format" value="^.*\*(?!.*(href|src)=).*?http.*$"/>
      <property name="message" value="Link in Javadoc must be tagged '&lt;a href=...'."/>
    </module>

    <!-- General Regexp -->
    <!-- Ensure no printing to console
    TODO there is an IDEA inspection for this
    -->
    <module name="RegexpSinglelineJava">
      <property name="format"
                value="((System\.(out|err))|printStackTrace|(out|err)\.(print|write|append))"/>
      <property name="ignoreComments" value="true"/>
      <property name="message" value="No printing to console, use more robust logging."/>
    </module>
    <!-- "legacy" core APIs that no one who values their livelihood should ever use
    TODO there is an IDEA inspection for this
    -->
    <module name="RegexpSinglelineJava">
      <property name="format" value="import java[.]util[.]Stack"/>
      <property name="ignoreComments" value="true"/>
      <property name="message"
                value="No usage of legacy Stack class, use ArrayDeque instead."/>
    </module>
    <module name="RegexpSinglelineJava">
      <property name="format" value="import java[.]util[.]Vector"/>
      <property name="ignoreComments" value="true"/>
      <property name="message"
                value="No usage of legacy Vector class, use ArrayList or CopyOnWriteArrayList instead."/>
    </module>
    <module name="RegexpSinglelineJava">
      <property name="format" value="import java[.]util[.]Hashtable"/>
      <property name="ignoreComments" value="true"/>
      <property name="message"
                value="No usage of legacy Hashtable class, use HashMap or ConcurrentHashMap instead."/>
    </module>
    <module name="RegexpSinglelineJava">
      <property name="format" value="import java[.](util|text)[.].*(Date|Calendar)"/>
      <property name="ignoreComments" value="true"/>
      <property name="message"
                value="No usage of legacy date classes, use java.time instead."/>
    </module>

    <!-- For explicitly disabling checks -->
    <module name="SuppressWithNearbyCommentFilter">
      <property name="commentFormat" value="CHECKSTYLE IGNORE (\w+) FOR NEXT (\d+) LINES"/>
      <property name="checkFormat" value="$1"/>
      <property name="influenceFormat" value="$2"/>
    </module>
  </module>
</module>