Switch expressions may have constant type and may be skipped during write

Reported here:
http://mail.openjdk.java.net/pipermail/compiler-dev/2018-November/012637.html

Source code:
---
public class Java12Test {
  public static void main(String[] args) {
    String s = "foo";
    System.out.println(s + switch(0) {
      default -> {
        s = "bar";
        break 1;
      }
    });
    System.out.println(s);
  }
}
---

Prints:
---
foo1
foo
---