Java 21 / JEP 441: Pattern Matching for switch result in com.palantir.javaformat.java.FormatterException

Java 21 / JEP 441 : Pattern Matching for switch code result in com.palantir.javaformat.java.FormatterException

What happened?

This method compiles using JDK 21:

class Example {
    static String test(CharSequence charSequence) {
        return switch (charSequence) {
            case String s when s.isEmpty() -> "empty string";
            case String s -> "non-empty string";
            default -> "not a String";
        };
    }
}

However, when using the spotless-maven-plugin together with <palantirJavaFormat> results in an exception:

mvn spotless:apply
[...]
Unable to format file [path to Example.java]: com.palantir.javaformat.java.FormatterException: error: expected token: 'when'; generated - instead -> [Help 1]

Maven config:

                <plugin>
                    <groupId>com.diffplug.spotless</groupId>
                    <artifactId>spotless-maven-plugin</artifactId>
                    <version>2.40.0</version>
                    <configuration>
                        <java>
                            <palantirJavaFormat>
                                <version>2.38.0</version>
                            </palantirJavaFormat>
                        </java>
                    </configuration>
                </plugin>

Maven:

mvn -v
Apache Maven 3.9.5 (57804ffe001d7215b5e7bcb531cf83df38f93546)
Java version: 21, vendor: Amazon.com Inc.
Default locale: en_GB, platform encoding: UTF-8
OS name: "mac os x", version: "13.6.1", arch: "x86_64", family: "mac"

What did you want to happen?

The maven-spotless-plugin and palanter-java-format should accept or reformat code that is supported by JDK 21

Start by reproducing the failure with JDK 21 and mvn spotless:apply using the shown spotless-maven-plugin and palantirJavaFormat configuration. Compare the formatter's handling of the JEP 441 when switch syntax with the reported expected token: 'when' error; done means the example is accepted or reformatted without FormatterException.