Support record patterns (preview-feature in Java 19) as described by JEP 405

[apflieger]

How it works Now:

Compilation works

javac --release 19 --enable-preview Example.java

Note: Example.java uses preview features of Java SE 19.
Note: Recompile with -Xlint:preview for details.

The source file

cat Example.java

class Example {

    record A(Object o) {}
    record B(Object o) {}

    void method(Object param) {
        switch (param) {
            case A(Object o) -> {}
            case B(var o) -> {}
            default -> {}
        }
        if (param instanceof A(var o)) {

        }
    }
}

Run checkstyle 10.5.0

RUN_LOCALE="-Duser.language=en -Duser.country=US"
java $RUN_LOCALE -jar checkstyle-10.5.0-all.jar -c /sun_checks.xml  Example.java

Starting audit...
com.puppycrawl.tools.checkstyle.api.CheckstyleException: Exception was thrown while processing Example.java
	at com.puppycrawl.tools.checkstyle.Checker.processFiles(Checker.java:307)
	at com.puppycrawl.tools.checkstyle.Checker.process(Checker.java:224)
	at com.puppycrawl.tools.checkstyle.Main.runCheckstyle(Main.java:415)
	at com.puppycrawl.tools.checkstyle.Main.runCli(Main.java:338)
	at com.puppycrawl.tools.checkstyle.Main.execute(Main.java:195)
	at com.puppycrawl.tools.checkstyle.Main.main(Main.java:130)
Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: IllegalStateException occurred while parsing file /Users/apflieger/src/sample-checkstyle-record-pattern/Example.java.
	at com.puppycrawl.tools.checkstyle.JavaParser.parse(JavaParser.java:105)
	at com.puppycrawl.tools.checkstyle.TreeWalker.processFiltered(TreeWalker.java:153)
	at com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck.process(AbstractFileSetCheck.java:98)
	at com.puppycrawl.tools.checkstyle.Checker.processFile(Checker.java:335)
	at com.puppycrawl.tools.checkstyle.Checker.processFiles(Checker.java:294)
	... 5 more
Caused by: java.lang.IllegalStateException: 9:12: no viable alternative at input 'switch(param){caseA(Objecto)->{}case'
	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.reportNoViableAlternative(DefaultErrorStrategy.java:310)
	at org.antlr.v4.runtime.DefaultErrorStrategy.reportError(DefaultErrorStrategy.java:136)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.statement(JavaLanguageParser.java:7050)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.blockStatement(JavaLanguageParser.java:6192)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.block(JavaLanguageParser.java:6095)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.methodBody(JavaLanguageParser.java:2938)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.methodDeclaration(JavaLanguageParser.java:2896)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.memberDeclaration(JavaLanguageParser.java:2743)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.classBodyDeclaration(JavaLanguageParser.java:2669)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.classBody(JavaLanguageParser.java:2475)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.classDeclaration(JavaLanguageParser.java:1094)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.types(JavaLanguageParser.java:751)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.typeDeclaration(JavaLanguageParser.java:665)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.compilationUnit(JavaLanguageParser.java:412)
	at com.puppycrawl.tools.checkstyle.JavaParser.parse(JavaParser.java:99)
	... 9 more
Caused by: org.antlr.v4.runtime.NoViableAltException
	at org.antlr.v4.runtime.atn.ParserATNSimulator.noViableAlt(ParserATNSimulator.java:2031)
	at org.antlr.v4.runtime.atn.ParserATNSimulator.execATN(ParserATNSimulator.java:470)
	at org.antlr.v4.runtime.atn.ParserATNSimulator.adaptivePredict(ParserATNSimulator.java:396)
	at com.puppycrawl.tools.checkstyle.grammar.java.JavaLanguageParser.statement(JavaLanguageParser.java:6723)
	... 21 more
Checkstyle ends with 1 errors.

Is your feature request related to a problem? Please describe.
This feature has been released in september 2022 as a preview feature. To me, given the trend of the recent java evolutions, it is very unlikely to be withdrawn.
Here's the jep https://openjdk.org/jeps/405

😇

Thank you for your awesome work 🙏

[nrmancuso]

I am on it.

[romani]

@apflieger , can we ask you to try workaround while fix is in progress ?

please try to apply this update to your config - #12542 (comment)
it should allow you to use new features without being blocked by checkstyle. Please share feedback.

[apflieger]

It works but other rules on the same file seem not to be executed then.

[nrmancuso]

It works but other rules on the same file seem not to be executed then.

Yes, TreeWalker checks (java code) will not work if file cannot be parsed. Checks that have Checker as a parent (FileSet) checks will still work with the file:

➜  src cat config.xml 
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
        "https://checkstyle.org/dtds/configuration_1_3.dtd">
<module name="Checker">
  <module name="RegexpSingleline">
    <property name="format" value="Object param"/>
    <property name="minimum" value="0"/>
    <property name="maximum" value="0"/>
  </module>
  <property name="haltOnException" value="false"/>
  <module name="SuppressionSingleFilter">
    <property name="message" value=".*IllegalStateException occurred while parsing file.*"/>
  </module>
  <module name="TreeWalker">
    <module name="IllegalIdentifierName"/>
  </module>
</module>

➜  src cat Test.java 
public class Test {
    record A(Object o) {}
    record B(Object o) {}

    void method(Object param) {
        switch (param) {
            case A(Object o) -> {}
            case B(var o) -> {}
            default -> {}
        }
        if (param instanceof A(var o)) {

        }
    }
}                                                                                                          

 ➜  src javac --enable-preview --release 19 Test.java            
Note: Test.java uses preview features of Java SE 19.
Note: Recompile with -Xlint:preview for details.

➜  src java -jar checkstyle-10.4-all.jar -c config.xml Test.java
Starting audit...
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:5: Line matches the illegal pattern 'Object param'. [RegexpSingleline]
Audit done.
Checkstyle ends with 1 errors.

Workaround at #12542 (comment) allows users to still use checkstyle, but not use TreeWalker checks on new syntax until support is added.

Edit: there is a nuance, modules are executed sequentially:

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

  <property name="haltOnException" value="false"/>
  <module name="SuppressionSingleFilter">
    <property name="message" value=".*IllegalStateException occurred while parsing file.*"/>
  </module>
  <module name="TreeWalker">
    <module name="IllegalIdentifierName"/>
  </module>
    <module name="RegexpSingleline">
    <property name="format" value="Object param"/>
    <property name="minimum" value="0"/>
    <property name="maximum" value="0"/>
  </module>
</module>
➜  src java -jar checkstyle-10.4-all.jar -c config.xml Test.java
Starting audit...
Audit done.

So, for this workaround to still allow other checks (non TreeWalker) to execute, they must appear in config BEFORE TreeWalker module.

[apflieger]

On my main project we have Checker rules like RegexpMultiline, they are declared before the TreeWalker module. These rules are sometimes executed, sometimes not. Weird, but it's not really a problem for me.

[romani]

@apflieger , if you move Treewalker in xml to be last child, execution will be more predictable.

[rnveach]

Fix was merged