When trying to use JEP 443: Unnamed Patterns and Variables (Preview) in JShell, I get the message that

> as of release 21, the underscore keyword '_' is only allowed to declare
> | unnamed patterns, local variables, exception parameters or lambda parameters

Full reproducer:

C:\Users\Johannes\dev\java>type Java21Test.java
import java.lang.invoke.MethodHandles;

public class Java21Test {
    public static void main(String[] args) throws Throwable {
        var _ = (String) MethodHandles.constant(String.class, "Hi").invokeExact();
    }
}

C:\Users\Johannes\dev\java>java --enable-preview --source 21 Java21Test.java
Note: Java21Test.java uses preview features of Java SE 21.
Note: Recompile with -Xlint:preview for details.

C:\Users\Johannes\dev\java>jshell --enable-preview
| Welcome to JShell -- Version 21-ea
| For an introduction type: /help intro

jshell> import java.lang.invoke.MethodHandles

jshell> var _ = (String) MethodHandles.constant(String.class, "Hi").invokeExact();
| Error:
| as of release 21, the underscore keyword '_' is only allowed to declare
| unnamed patterns, local variables, exception parameters or lambda parameters
| var _ = (String) MethodHandles.constant(String.class, "Hi").invokeExact();
| ^

This error message is surprising, as to my knowledge `var` can only be used for local variables, therefore allowing the use of `_` as variable name as well.