Checkstyle fails to parse unnamed variable

[nrmancuso]

Reading: https://openjdk.org/jeps/456#:~:text=An%20unnamed%20variable%20is%20declared,parameter%20in%20a%20lambda%20expression.

Summary
Enhance the Java programming language with unnamed variables and unnamed patterns, which can be used when variable declarations or nested patterns are required but never used. Both are denoted by the underscore character, _.

Example:

➜  src cat UnnamedVariable.java                        
public class UnnamedVariable {
    record R(int x) {}
    void m(Object o) {
        if (o instanceof R(_)) {}
    }
}
➜  src javac --release 21 --enable-preview UnnamedVariable.java 
Note: UnnamedVariable.java uses preview features of Java SE 21.
Note: Recompile with -Xlint:preview for details.
➜  src java -jar checkstyle-10.12.3-all.jar -t UnnamedVariable.java 
com.puppycrawl.tools.checkstyle.api.CheckstyleException: IllegalStateException occurred while parsing file /home/nick/IdeaProjects/tester/src/UnnamedVariable.java.
        at com.puppycrawl.tools.checkstyle.JavaParser.parse(JavaParser.java:105)
        at com.puppycrawl.tools.checkstyle.JavaParser.parseFileText(JavaParser.java:122)
        at com.puppycrawl.tools.checkstyle.JavaParser.parseFile(JavaParser.java:142)
        at com.puppycrawl.tools.checkstyle.AstTreeStringPrinter.printFileAst(AstTreeStringPrinter.java:65)
        at com.puppycrawl.tools.checkstyle.Main.runCli(Main.java:291)
        at com.puppycrawl.tools.checkstyle.Main.execute(Main.java:195)
        at com.puppycrawl.tools.checkstyle.Main.main(Main.java:130)
Caused by: java.lang.IllegalStateException: 4:26: mismatched input '(' expecting ')'
        at com.puppycrawl.tools.checkstyle.JavaParser$CheckstyleErrorListener.syntaxError(JavaParser.java:255)
        at org.antlr.v4.runtime.ProxyErrorListener.syntaxError(ProxyErrorListener.java:41)
        at org.antlr.v4.runtime.Parser.notifyErrorListeners(Parser.java:544)
        at org.antlr.v4.runtime.DefaultErrorStrategy.reportInputMismatch(DefaultErrorStrategy.java:327)
        at org.antlr.v4.runtime.DefaultErrorStrategy.reportError(DefaultErrorStrategy.java:139)
        at com.puppycrawl.tools.checkstyle.CheckstyleParserErrorStrategy.recoverInline(CheckstyleParserErrorStrategy.java:38)
        at org.antlr.v4.runtime.Parser.match(Parser.java:208)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.parExpression(JavaLanguageParser.java:8753)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.statement(JavaLanguageParser.java:6769)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.blockStatement(JavaLanguageParser.java:6198)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.block(JavaLanguageParser.java:6101)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.methodBody(JavaLanguageParser.java:2940)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.methodDeclaration(JavaLanguageParser.java:2898)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.memberDeclaration(JavaLanguageParser.java:2745)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.classBodyDeclaration(JavaLanguageParser.java:2671)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.classBody(JavaLanguageParser.java:2477)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.classDeclaration(JavaLanguageParser.java:1096)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.types(JavaLanguageParser.java:753)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.typeDeclaration(JavaLanguageParser.java:667)
        at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.compilationUnit(JavaLanguageParser.java:414)
        at com.puppycrawl.tools.checkstyle.JavaParser.parse(JavaParser.java:99)
        ... 6 more
Caused by: org.antlr.v4.runtime.InputMismatchException
        ... 22 more
Checkstyle ends with 1 errors.

[nrmancuso]

Completed via #14025 (review)

[rnveach]

@nrmancuso Has there been any review on which modules should be changed for this new antlr?

[nrmancuso]

Yes, I will open a WIP issue to track this.

[nrmancuso]

Done at #14444