kernel-checkstyle.xml

<!--
  ~ 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.
  ~ The ASF licenses this file to You 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.
  -->

<!DOCTYPE module PUBLIC
        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
        "https://checkstyle.org/dtds/configuration_1_3.dtd">

<!--

    Checkstyle configuration based on the Google coding conventions from:

    -  Google Java Style
       https://google.github.io/styleguide/javaguide.html

    with Spark-specific changes from:

    https://spark.apache.org/contributing.html#code-style-guide

    Checkstyle is very configurable. Be sure to read the documentation at
    http://checkstyle.sf.net (or in your downloaded distribution).

    Most Checks are configurable, be sure to consult the documentation.

    To completely disable a check, just comment it out or delete it from the file.

    Authors: Max Vetrenko, Ruslan Diachenko, Roman Ivanov.

 -->

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

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

    <property name="fileExtensions" value="java, properties, xml"/>

    <module name="SuppressionFilter">
        <property name="file" value="dev/checkstyle-suppressions.xml"/>
    </module>

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

    <module name="RegexpSingleline">
        <!-- \s matches whitespace character, $ matches end of line. -->
        <property name="format" value="\s+$"/>
        <property name="message" value="No trailing whitespace allowed."/>
    </module>

    <module name="LineLength">
        <property name="max" value="100"/>
        <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>
    </module>

    <module name="NewlineAtEndOfFile"/>

    <module name="RegexpHeader">
        <property name="headerFile" value="dev/copyrightHeader"/>
    </module>

    <module name="TreeWalker">
        <!--
        If you wish to turn off checking for a section of code, you can put a comment in the source
        before and after the section, with the following syntax:

          // checkstyle.off: XXX (such as checkstyle.off: NoFinalizer)
          ...  // stuff that breaks the styles
          // checkstyle.on: XXX (such as checkstyle.on: NoFinalizer)
        -->
        <module name="SuppressionCommentFilter">
            <property name="offCommentFormat" value="checkstyle\.off\: ([\w\|]+)"/>
            <property name="onCommentFormat" value="checkstyle\.on\: ([\w\|]+)"/>
            <property name="checkFormat" value="$1"/>
        </module>
        <module name="OuterTypeFilename"/>
        <module name="IllegalTokenText">
            <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>
            <property name="format" value="\\u00(08|09|0(a|A)|0(c|C)|0(d|D)|22|27|5(C|c))|\\(0(10|11|12|14|15|42|47)|134)"/>
            <property name="message" value="Avoid using corresponding octal or Unicode escape."/>
        </module>
        <module name="AvoidEscapedUnicodeCharacters">
            <property name="allowEscapesForControlCharacters" value="true"/>
            <property name="allowByTailComment" value="true"/>
            <property name="allowNonPrintableEscapes" value="true"/>
        </module>
        <module name="NoLineWrap"/>
        <module name="EmptyBlock">
            <property name="option" value="TEXT"/>
            <property name="tokens" value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
        </module>
        <module name="NeedBraces">
            <property name="allowSingleLineStatement" value="true"/>
        </module>
        <module name="OneStatementPerLine"/>
        <module name="ArrayTypeStyle"/>
        <module name="FallThrough"/>
        <module name="UpperEll"/>
        <module name="ModifierOrder"/>
        <module name="SeparatorWrap">
            <property name="tokens" value="DOT"/>
            <property name="option" value="nl"/>
        </module>
        <module name="SeparatorWrap">
            <property name="tokens" value="COMMA"/>
            <property name="option" value="EOL"/>
        </module>
        <module name="PackageName">
            <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]*)*$"/>
            <message key="name.invalidPattern"
                     value="Package name ''{0}'' must match pattern ''{1}''."/>
        </module>
        <module name="ClassTypeParameterName">
            <property name="format" value="([A-Z][a-zA-Z0-9]*$)"/>
            <message key="name.invalidPattern"
                     value="Class type name ''{0}'' must match pattern ''{1}''."/>
        </module>
        <module name="MethodTypeParameterName">
            <property name="format" value="([A-Z][a-zA-Z0-9]*)"/>
            <message key="name.invalidPattern"
                     value="Method type name ''{0}'' must match pattern ''{1}''."/>
        </module>
        <module name="GenericWhitespace">
            <message key="ws.followed"
                     value="GenericWhitespace ''{0}'' is followed by whitespace."/>
            <message key="ws.preceded"
                     value="GenericWhitespace ''{0}'' is preceded with whitespace."/>
            <message key="ws.illegalFollow"
                     value="GenericWhitespace ''{0}'' should followed by whitespace."/>
            <message key="ws.notPreceded"
                     value="GenericWhitespace ''{0}'' is not preceded with whitespace."/>
        </module>
        <module name="MethodParamPad"/>
        <module name="AnnotationLocation">
            <property name="tokens" value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF"/>
        </module>
        <module name="AnnotationLocation">
            <property name="tokens" value="VARIABLE_DEF"/>
            <property name="allowSamelineMultipleAnnotations" value="true"/>
        </module>
        <module name="MethodName">
            <property name="format" value="^[a-z][a-z0-9][a-zA-Z0-9_]*$"/>
            <message key="name.invalidPattern"
                     value="Method name ''{0}'' must match pattern ''{1}''."/>
        </module>
        <module name="EmptyCatchBlock">
            <property name="exceptionVariableName" value="expected"/>
        </module>
        <module name="UnusedImports"/>
        <module name="RedundantImport"/>
        <module name="RedundantModifier"/>
        <module name="RegexpSinglelineJava">
            <property name="format" value="throw new \w+Error\("/>
            <property name="message" value="Avoid throwing error in application code."/>
        </module>
        <module name="RegexpSinglelineJava">
            <property name="format" value="Objects\.toStringHelper"/>
            <property name="message" value="Avoid using Object.toStringHelper. Use ToStringBuilder instead." />
        </module>
        <module name="RegexpSinglelineJava">
            <property name="format" value="new (java\.lang\.)?(Byte|Integer|Long|Short)\("/>
            <property name="message" value="Use static factory 'valueOf' or 'parseXXX' instead of the deprecated constructors." />
        </module>

        <!--
        As per https://checkstyle.sourceforge.io/config_imports.html, "There is no flexibility to
        enforce empty lines between some groups and no empty lines between other groups." However,
        sometimes we want import X to come before import Y, yet we do not want them to be separated
        by a blank line. This suppression is how we achieve that.
        -->
        <!-- io.delta.kernel and io.delta.kernel.internal -->
        <module name="SuppressionXpathSingleFilter">
            <property name="checks" value="ImportOrder"/>
            <property name="message" value="^'io.delta.kernel.internal\..*'.*"/>
        </module>

        <!-- io.delta.kernel.defaults and io.delta.kernel.defaults.internal -->
        <module name="SuppressionXpathSingleFilter">
            <property name="checks" value="ImportOrder"/>
            <property name="message" value="^'io.delta.kernel.defaults.internal\..*'.*"/>
        </module>

        <!-- java and javax -->
        <module name="SuppressionXpathSingleFilter">
            <property name="checks" value="ImportOrder"/>
            <property name="message" value="^'javax\..*'.*"/>
        </module>
    </module>
</module>