[patterns] Redefinition of pattern variable is allowed by javac in some cases

[Tagir Valeev]

Hello!

Playing with javac 14-ea+28-1366. This code can be successfully compiled:

class Test {
  static void test(Object o1, Object o2) {
      boolean b = o1 instanceof String s && (!(o2 instanceof String s)
|| consume(s));
  }

  static boolean consume(String s) {
     System.out.println(s);
     return true;
  }

  public static void main(String[] args) {
    test("x", "y"); // prints y
  }
}

Spec draft says for `a || b`:
It is a compile-time error if any pattern variable introduced by a
when false is already in scope at b.

If I understand correctly, assuming a = !(o2 instanceof String s) and
b = consume(s), we already have `s` (from `o1 instanceof String s`) in
the scope at b, and a introduces new `s` when false, so this code
should be rejected. Please correct me if I am wrong.

With best regards,
Tagir Valeev.