checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.2//EN" "http://www.puppycrawl.com/dtds/configuration_1_2.dtd">
<module name="Checker">
	<property name="charset" value="UTF-8"/>
	<property name="fileExtensions" value="java"/>
	<property name="localeLanguage" value="en"/>
	<property name="localeCountry" value="US"/>
	<property name="tabWidth" value="4"/>

	<module name="NewlineAtEndOfFile"/>

	<!-- disallow trailing whitespace -->
	<module name="RegexpSingleline">
		<property name="format" value="\s+$"/>
		<property name="message" value="trailing whitespace"/>
	</module>

	<!-- note: RegexpMultiline shows nicer messages than Regexp, but has to be outside TreeWalker -->
	<!-- disallow multiple consecutive blank lines -->
	<module name="RegexpMultiline">
		<property name="format" value="\n[\t ]*\r?\n[\t ]*\r?\n"/>
		<property name="message" value="adjacent blank lines"/>
	</module>

	<!-- disallow blank after { -->
	<module name="RegexpMultiline">
		<property name="format" value="\{[\t ]*\r?\n[\t ]*\r?\n"/>
		<property name="message" value="blank line after '{'"/>
	</module>

	<!-- disallow blank before } -->
	<module name="RegexpMultiline">
		<property name="format" value="\n[\t ]*\r?\n[\t ]*\}"/>
		<property name="message" value="blank line before '}'"/>
	</module>

	<!-- require blank before { in the same indentation level -->
	<module name="RegexpMultiline">
		<!-- the regex works as follows:
		It matches (=fails) for \n<indentation><something>\n<same indentation><control statement>[...]{\n
		while <something> is a single line comment, it'll look for a blank line one line earlier
		if <something> is a space, indicating a formatting error or ' */', it'll ignore the instance
		if <something> is a tab, indicating a continued line, it'll ignore the instance
		<control statement> is 'if', 'do', 'while', 'for', 'try' or nothing (instance initializer block)

		- first \n: with positive lookbehind (?<=\n) to move the error marker to a more reasonable place
		- capture tabs for <indentation>, later referenced via \1
		- remaining preceding line as a non-comment (doesn't start with '/', '//', ' ' or '\t') or multiple lines where all but the first are a single line comment with the same indentation
		- new line
		- <indentation> as captured earlier
		- <control statement> as specified above
		- { before the next new line -->
		<property name="format" value="(?&lt;=\n)([\t]+)(?:[^/\r\n \t][^\r\n]*|/[^/\r\n][^\r\n]*|[^/\r\n][^\r\n]*(\r?\n\1//[^\r\n]*)+)\r?\n\1(|(if|do|while|for|try)[^\r\n]+)\{[\t ]*\r?\n"/>
		<property name="message" value="missing blank line before block at same indentation level"/>
	</module>

	<!-- require blank after } in the same indentation level -->
	<module name="RegexpMultiline">
		<!-- \n<indentation>}\n<same indentation><whatever unless newline, '}' or starting with cas(e) or def(ault)> -->
		<property name="format" value="(?&lt;=\n)([\t]+)\}\r?\n\1(?:[^\r\n\}cd]|c[^\r\na]|ca[^\r\ns]|d[^\r\ne]|de[^\r\nf])"/>
		<property name="message" value="missing blank line after block at same indentation level"/>
	</module>

	<module name="TreeWalker">
        <!-- Allow "//CHECKSTYLE.OFF: <InspectionName>" and "//CHECKSTYLE.ON: <InspectionName>" pairs to toggle some inspections -->
        <module name="SuppressionCommentFilter">
            <property name="offCommentFormat" value="CHECKSTYLE.OFF\: ([\w\|]+)"/>
            <property name="onCommentFormat" value="CHECKSTYLE.ON\: ([\w\|]+)"/>
            <property name="checkFormat" value="$1"/>
        </module>

		<!-- Ensure all imports are ship shape -->
		<module name="AvoidStarImport"/>
		<module name="IllegalImport"/>
		<module name="RedundantImport"/>
		<module name="UnusedImports"/>

		<module name="ImportOrder">
			<property name="groups" value="java,javax,*,net.minecraft,net.fabricmc"/>
			<property name="ordered" value="true"/>
			<property name="separated" value="true"/>
			<property name="option" value="top"/>
			<property name="sortStaticImportsAlphabetically" value="true"/>
		</module>

		<!-- Ensures braces are at the end of a line -->
		<module name="LeftCurly"/>
		<module name="RightCurly"/>

		<!-- single line statements on one line, -->
		<module name="NeedBraces">
			<property name="tokens" value="LITERAL_IF,LITERAL_FOR,LITERAL_WHILE"/>
			<property name="allowSingleLineStatement" value="true"/>
		</module>
		<module name="NeedBraces">
			<property name="tokens" value="LITERAL_ELSE,LITERAL_DO"/>
			<property name="allowSingleLineStatement" value="false"/>
		</module>

		<module name="EmptyLineSeparator">
			<property name="allowNoEmptyLineBetweenFields" value="true"/>
			<property name="allowMultipleEmptyLines" value="false"/>
			<!-- exclude  METHOD_DEF and VARIABLE_DEF -->
			<property name="tokens" value="PACKAGE_DEF,IMPORT,STATIC_IMPORT,CLASS_DEF,INTERFACE_DEF,ENUM_DEF,STATIC_INIT,INSTANCE_INIT,CTOR_DEF"/>
		</module>

		<module name="OperatorWrap"/>
		<module name="SeparatorWrap">
			<property name="tokens" value="DOT,ELLIPSIS,AT"/>
			<property name="option" value="nl"/>
		</module>
		<module name="SeparatorWrap">
			<property name="tokens" value="COMMA,SEMI"/>
			<property name="option" value="eol"/>
		</module>

		<module name="Indentation">
			<property name="basicOffset" value="4"/>
			<property name="caseIndent" value="0"/>
			<property name="throwsIndent" value="4"/>
			<property name="arrayInitIndent" value="4"/>
			<property name="lineWrappingIndentation" value="8"/>
		</module>

		<module name="ParenPad"/>
		<module name="NoWhitespaceBefore"/>
		<module name="NoWhitespaceAfter">
			<!-- allow ARRAY_INIT -->
			<property name="tokens" value="AT,INC,DEC,UNARY_MINUS,UNARY_PLUS,BNOT,LNOT,DOT,ARRAY_DECLARATOR,INDEX_OP"/>
		</module>
		<module name="WhitespaceAfter"/>
		<module name="WhitespaceAround">
			<!-- Allow PLUS, MINUS, MUL, DIV as they may be more readable without spaces in some cases -->
			<property name="tokens" value="ASSIGN,BAND,BAND_ASSIGN,BOR,BOR_ASSIGN,BSR,BSR_ASSIGN,BXOR,BXOR_ASSIGN,COLON,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_ASSIGN,MOD,MOD_ASSIGN,NOT_EQUAL,PLUS_ASSIGN,QUESTION,RCURLY,SL,SLIST,SL_ASSIGN,SR,SR_ASSIGN,STAR,STAR_ASSIGN,LITERAL_ASSERT,TYPE_EXTENSION_AND"/>
		</module>
		<module name="SingleSpaceSeparator"/>
		<module name="GenericWhitespace"/>
		<module name="CommentsIndentation"/>

		<module name="ArrayTypeStyle"/>
		<module name="DefaultComesLast">
			<property name="skipIfLastAndSharedWithCase" value="true"/>
		</module>
		<module name="SimplifyBooleanExpression"/>
		<module name="SimplifyBooleanReturn"/>
		<module name="StringLiteralEquality"/>

		<module name="ModifierOrder"/>
		<module name="RedundantModifier"/>

		<module name="AnnotationLocation"/>
		<module name="MissingOverride"/>

		<!-- By default this allows catch blocks with only comments -->
		<module name="EmptyCatchBlock"/>

		<!-- Enforce tabs -->
		<module name="RegexpSinglelineJava">
			<property name="format" value="^\t* ([^*]|\*[^ /])"/>
			<property name="message" value="non-tab indentation"/>
		</module>

		<module name="OuterTypeFilename"/>
		<module name="PackageDeclaration"/>
		<module name="PackageName">
			<!-- require a package following the following structure:
			base package name: net.fabricmc.fabric
			+ api/implementation/mixin subpackage: api/impl/mixin
			+ client/dedicated server/common env subpackage: client/server/<nothing>
			+ module name subpackage, singular, may contain multiple .-separated parts
			+ api mandatory: module major version with v prefix (e.g. v1)
			+ other subpackages as needed, all singular

			The regex works as follows:
			It matches (=succeeds) for one of these cases:
			- net.fabricmc.fabric.api.client.<module-name>.v<version>[.<extra packages...>]
			- net.fabricmc.fabric.api.server.<module-name>.v<version>[.<extra packages...>]
			- net.fabricmc.fabric.api.<module-name>.v<version>[.<extra packages...>]
			- net.fabricmc.fabric.(impl|mixin).client.<module-name>[.v<version>][.<extra packages...>]
			- net.fabricmc.fabric.(impl|mixin).server.<module-name>[.v<version>][.<extra packages...>]
			- net.fabricmc.fabric.(impl|mixin).<module-name>[.v<version>][.<extra packages...>]
			- <any legacy package>
			where <module-name> is a set of '.'-separated words, all in singular (not ending with s except for ss) and not starting with client. or server.
			and <version> is a non-negative integer (0, 1, 2, 3, ...)
			and <extra packages...> is a set of '.'-separated words with all the first potentially containing digits.
			Negative lookahead ensures that client/server can't be replaced with common disguised as the module name.

			The regex is implemented in 3 parts:
			- the net.fabricmc.fabric. prefix
			- patterns for
				- api packages: api + <not common> + client/server/nothing + <module-name> + 'v' + <version>
				- impl+mixin packages : impl/mixin + <not common> + client/server/nothing + <module-name>
				- literal legacy packages (exceptions)
			- largely unconstained trailing subpackages
			-->
			<property name="format"
			value="^net\.fabricmc\.fabric\.(api(?!\.common\.)(\.client|\.server|)(\.(?!client\.|server\.)[a-z]+([a-rt-z]|ss))+\.v[0-9]+|(impl|mixin|test)(?!\.common\.)(\.client|\.server|)(\.(?!client\.|server\.)[a-z]+([a-rt-z]|ss))+(\.v[0-9]+)?|api\.(event|util|biomes\.v1|registry|client\.screen|container|block|entity|client\.itemgroup|client\.keybinding|tag|tools|client\.model|network|server|client\.render|resource|client\.texture))(|\.[a-z]+(\.[a-z0-9]+)*)$"/>
		</module>

		<!--<module name="InvalidJavadocPosition"/>-->
		<module name="JavadocParagraph"/>
		<module name="JavadocStyle"/>
		<module name="AtclauseOrder">
			<property name="tagOrder" value="@param,@return,@throws,@deprecated"/>
		</module>

        <!-- Prevent var for all cases other than new instance creation -->
        <module name="MatchXpath">
            <property name="query" value="//VARIABLE_DEF[./TYPE/IDENT[@text='var'] and not(./ASSIGN/EXPR/LITERAL_NEW)]"/>
        </module>

        <!-- Prevent public records in API packages -->
        <module name="MatchXpath">
            <property name="query" value="//RECORD_DEF[./MODIFIERS/LITERAL_PUBLIC][//PACKAGE_DEF//DOT/IDENT[@text='api']]"/>
        </module>
	</module>
</module>