Inference of recursive types

[Liam Miller-Cushon]

Hi -

Sorry if this has already been discussed, but I ran into a difference in
behaviour between javac8 -source 7/-target 7 and both javac7 and javac8
-source 8/-target 8.

The following program compiles with everything except javac8 -source
7/-target 7.

Is this an intentional change? Having to make g's type parameter explicit
feels like a regression.

===
class Test {
  static class One<T> {}
  static class Two extends One<Two> {}

  <T extends One<T>> T f(T a, String s) {
    T t = g(s);
    return t;
  }
  static <U extends One<U>> U g(String s) {
    throw new RuntimeException();
  }
}
===

Test.java:6: error: incompatible types: inference variable U#1 has
incompatible upper bounds One<U#2>,T
    T t = g(s);
           ^
  where U#1,U#2,T are type-variables:
    U#1 extends One<U#1> declared in method <U#1>g(String)
    U#2 extends T
    T extends One<T> declared in method <T>f(T,String)
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