Possible bug in javac 8 'legacy' type inference

Liam Miller-Cushon cushon at google.com
Thu Nov 14 09:31:34 PST 2013

The following program compiles with javac 7, and with javac 8 using -source

However, when compiled with javac 8 and -source 7 an inference error is

incompatible types: inference variable T#1 has incompatible upper bounds
    Result result = getThing(key);
  where T#1,T#2 are type-variables:
    T#1 extends Message<T#1> declared in method <T#1>getThing(Key)
    T#2 extends Result

Is this a bug, or is javac 8 more accurately reflecting the intent of JLS


class Message<T extends Message<T>> {}
class Key extends Message<Key> {}
class Result extends Message<Result> {}

abstract class Foo {
  abstract <T extends Message<T>> T getThing(Key key);

  void test(Key key) {
    Result result = getThing(key);

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