RFR: 8271623: Omit enclosing instance fields from inner classes that don't use it

[liach]

On Tue, 3 Aug 2021 03:19:13 GMT, Liam Miller-Cushon <cushon at openjdk.org> wrote:

> This change omits the synthetic `this$0` field from inner classes that do not access any enclosing instance state.

I hope we have a test case that ensures the field is not erroneously removed when this nested class doesn't use the field, but another nested class within this nested class does. An example:


public class Second {

  int t = 3;

  public static void main(String... a) {
    var q = new Second();
    var p = q.new Third().new Fourth();
    q.t = 6;
    p.print();
  }
  
  public class Third {
    public class Fourth {
      public void print() {
        System.out.println(Second.this.t);
      }
    }
  }
}

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PR: https://git.openjdk.java.net/jdk/pull/4966