Incompatibility with Java 21

[steffenvan]

What happened?

When I run this formatter with mvn spotless:check with this code:

...
return switch (object) {
    case SomeType t when t.hasConditionA() ->
        processConditionA(x);
    case SomeOtherType t when t.hasConditionB() ->
        processConditionB(x);
    default -> {
        var result = computeDefaultResult(x);
        yield updateResult(object, result);
    }
};
...

I get the following error:

[ERROR] Step 'palantir-java-format' found problem in 'src/main/java/com/organization/project/file.java':
121:19: error: expected token: 'when'; generated - instead
com.palantir.javaformat.java.FormatterException: 121:19: error: expected token: 'when'; generated - instead
    at com.palantir.javaformat.java.Formatter.getFormatReplacements (Formatter.java:315)
    at com.palantir.javaformat.java.Formatter.formatSource (Formatter.java:290)
    at com.palantir.javaformat.java.Formatter.formatSource (Formatter.java:245)
    at com.diffplug.spotless.glue.pjf.PalantirJavaFormatFormatterFunc.apply (PalantirJavaFormatFormatterFunc.java:55)
    at com.diffplug.spotless.FormatterFunc.apply (FormatterFunc.java:32)
    at com.diffplug.spotless.FormatterStepImpl$Standard.format (FormatterStepImpl.java:82)
    at com.diffplug.spotless.FormatterStep$Strict.format (FormatterStep.java:103)
    at com.diffplug.spotless.Formatter.compute (Formatter.java:246)
    at com.diffplug.spotless.PaddedCell.calculateDirtyState (PaddedCell.java:203)
    at com.diffplug.spotless.PaddedCell.calculateDirtyState (PaddedCell.java:190)
    at com.diffplug.spotless.maven.SpotlessCheckMojo.process (SpotlessCheckMojo.java:56)
    at com.diffplug.spotless.maven.AbstractSpotlessMojo.execute (AbstractSpotlessMojo.java:237)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:126)
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:328)
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:316)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:212)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:174)
    at org.apache.maven.lifecycle.internal.MojoExecutor.access$000 (MojoExecutor.java:75)
    at org.apache.maven.lifecycle.internal.MojoExecutor$1.run (MojoExecutor.java:162)
    at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute (DefaultMojosExecutionStrategy.java:39)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:159)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:105)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:73)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:53)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:118)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:261)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:173)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:101)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:903)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:280)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:203)
    at jdk.internal.reflect.DirectMethodHandleAccessor.invoke (DirectMethodHandleAccessor.java:103)
    at java.lang.reflect.Method.invoke (Method.java:580)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:255)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:201)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:361)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:314)

My pom file looks like:

<plugin>
    <groupId>com.diffplug.spotless</groupId>
    <artifactId>spotless-maven-plugin</artifactId>
    <version>2.43.0</version>
    <configuration>
        <java>
            <palantirJavaFormat>
                <version>2.50.0</version>                    
                <style>PALANTIR</style>                      
                <formatJavadoc>false</formatJavadoc>
            </palantirJavaFormat>
        </java>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>apply</goal>
            </goals>
            <phase>compile</phase>
        </execution>
    </executions>
</plugin>

What did you want to happen?

It shouldn't fail to run the formatter with this code. This is code for Java 21, so I suspect there is an issue here?

[talios]

This would be a duplicate of #952.