This program should compile (with --enable-preview) but fails instead:

$ cat C.java
class C {
    C() {
        Runnable r = () -> {
            return;
        };
        super();
    }
}
$ javac -d classes --enable-preview --release 23 C.java
C.java:4: error: 'return' not allowed before explicit constructor invocation
            return;
            ^
Note: C.java uses preview features of Java SE 23.
Note: Recompile with -Xlint:preview for details.