Rxjava: compilation error with jdk9

[cushon]

The jdk9 javac contains breaking changes to type inference, even for compilations targeting older language versions: https://bugs.openjdk.java.net/browse/JDK-8075793?focusedCommentId=13865850

Those changes prevent RxJava from building with jdk9.

Repro:

$ java -fullversion
java full version "1.9.0-ea-b80"
$ ./gradlew build
...
./src/main/java/rx/Observable.java:520: error: incompatible types: Observable<CAP#1> cannot be converted to Observable<R>
        return combineLatest(Arrays.asList(o1, o2), Functions.fromFunc(combineFunction));
                            ^
  where R,T1,T2 are type-variables:
    R extends Object declared in method <T1,T2,R>combineLatest(Observable<? extends T1>,Observable<? extends T2>,Func2<? super T1,? super T2,? extends R>)
    T1 extends Object declared in method <T1,T2,R>combineLatest(Observable<? extends T1>,Observable<? extends T2>,Func2<? super T1,? super T2,? extends R>)
    T2 extends Object declared in method <T1,T2,R>combineLatest(Observable<? extends T1>,Observable<? extends T2>,Func2<? super T1,? super T2,? extends R>)
  where CAP#1 is a fresh type-variable:
    CAP#1 extends R from capture of ? extends R
...
38 errors

[akarnokd]

Thanks. Type inference has been of trouble lately, especially the discrepancy between javac and Eclipse for me. I'll try to fix these errors. The problem is that java doesn't support co- and contravariant type parameters in class definitions unlike C# thus Observable<T> != Observable<? extends T>

[akarnokd]

I'm closing this issue due to inactivity. If you have further input on the issue, don't hesitate to reopen this issue or post a new one.

[cushon]

RxJava still doesn't build with jdk9.

[akarnokd]

I'll look into it.

[akarnokd]

Posted the proposed changes in #3824. Could you verify it?

[cushon]

I verified that it compiles with javac9 and the default language level, but it doesn't compile with -source 1.6 -target 1.6 which is what the gradle build uses.

Here are the other errors I get: https://gist.github.com/cushon/1330f5b61c0d36d362eebca67c7a505a

[akarnokd]

Updated the PR. Tested with both default and 1.6 source/targets with 9b111.

[cushon]

Looks good to me, thanks!

[akarnokd]

Should be resolved by now.