feat: support sealed classes

[clementdessoude]

What changed with this PR:

Support sealed classes and interfaces

Example

// Input
public sealed class Rectangle
    implements Shape
    permits Square {

    private final double length;
    private final double height;

    public Rectangle(double length, double height) {
        this.length = length;
        this.height = height;
    }

    @Override
    public double area() {
        return length * height;
    }

}

public non-sealed class RightTriangle implements Triangle {

    private final double adjacent;
    private final double opposite;

    public RightTriangle(double adjacent, double opposite) {
        this.adjacent = adjacent;
        this.opposite = opposite;
    }

    @Override
    public double area() {
        interface People { String name(); }
        record Person(String name) implements People { }
        record Persons(String... names) { }

        People p = new Person("John Doe");

        return adjacent * opposite / 2;
    }

}

public sealed interface Shape
    permits Circle, Rectangle, Triangle, Unicorn {

    double area();

    default Shape rotate(double angle) {
        return this;
    }

    default String areaMessage() {
        if (this instanceof Circle)
            return "Circle: " + area();
        else if (this instanceof Rectangle)
            return "Rectangle: " + area();
        else if (this instanceof RightTriangle)
            return "Triangle: " + area();
        // :(
        throw new IllegalArgumentException();
    }

}

public non-sealed interface Triangle extends Shape {

}

public sealed interface Shape permits ALongVeryLongCircle, ALongVeryLongRectangle, ALongVeryLongTriangle, ALongVeryLongUnicorn {}
public sealed interface Shape extends AbstractShape permits ALongVeryLongCircle, ALongVeryLongRectangle, ALongVeryLongTriangle, ALongVeryLongUnicorn {}
public sealed class Shape permits ALongVeryLongCircle, ALongVeryLongRectangle, ALongVeryLongTriangle, ALongVeryLongUnicorn {}
public sealed class Shape extends AbstractShape permits ALongVeryLongCircle, ALongVeryLongRectangle, ALongVeryLongTriangle, ALongVeryLongUnicorn {}

// Output
public sealed class Rectangle implements Shape permits Square {

  private final double length;
  private final double height;

  public Rectangle(double length, double height) {
    this.length = length;
    this.height = height;
  }

  @Override
  public double area() {
    return length * height;
  }
}

public non-sealed class RightTriangle implements Triangle {

  private final double adjacent;
  private final double opposite;

  public RightTriangle(double adjacent, double opposite) {
    this.adjacent = adjacent;
    this.opposite = opposite;
  }

  @Override
  public double area() {
    interface People {
      String name();
    }
    record Person(String name) implements People {}
    record Persons(String... names) {}

    People p = new Person("John Doe");

    return adjacent * opposite / 2;
  }
}

public sealed interface Shape permits Circle, Rectangle, Triangle, Unicorn {
  double area();

  default Shape rotate(double angle) {
    return this;
  }

  default String areaMessage() {
    if (this instanceof Circle) return "Circle: " + area(); else if (
      this instanceof Rectangle
    ) return "Rectangle: " + area(); else if (
      this instanceof RightTriangle
    ) return "Triangle: " + area();
    // :(
    throw new IllegalArgumentException();
  }
}

public non-sealed interface Triangle extends Shape {}

public sealed interface Shape
  permits
    ALongVeryLongCircle,
    ALongVeryLongRectangle,
    ALongVeryLongTriangle,
    ALongVeryLongUnicorn {}

public sealed interface Shape
  extends AbstractShape
  permits
    ALongVeryLongCircle,
    ALongVeryLongRectangle,
    ALongVeryLongTriangle,
    ALongVeryLongUnicorn {}

public sealed class Shape
  permits
    ALongVeryLongCircle,
    ALongVeryLongRectangle,
    ALongVeryLongTriangle,
    ALongVeryLongUnicorn {}

public sealed class Shape
  extends AbstractShape
  permits
    ALongVeryLongCircle,
    ALongVeryLongRectangle,
    ALongVeryLongTriangle,
    ALongVeryLongUnicorn {}

Relative issues or prs:

Should fix #435