Bug 454497

Description Trejkaz pen name 2014-12-08 19:31:59 EST

We have the following code in our project which implements a collector to Guava's ImmutableList. It compiles fine with javac (and which IDEA does not note as a syntax error either):

    public static <T> Collector<T, ?, ImmutableList<T>> toImmutableList1()
    {
        return Collector.<T, ImmutableList.Builder<T>, ImmutableList<T>>of(
            ImmutableList::builder,
            ImmutableList.Builder::add,
            (left, right) -> left.addAll(right.build()),
            ImmutableList.Builder::build);
    }

Eclipse lights up with 5 errors. It seems to pick the wrong Collector.of and mistake the types of pretty much every parameter.

To help it out, I thought I would try adding explicit casts:

    public static <T> Collector<T, ?, ImmutableList<T>> toImmutableList()
    {
        return Collector.<T, ImmutableList.Builder<T>, ImmutableList<T>>of(
            (Supplier<ImmutableList.Builder<T>>) ImmutableList::builder,
            (BiConsumer<ImmutableList.Builder<T>, T>) ImmutableList.Builder::add,
            (BinaryOperator<ImmutableList.Builder<T>>) (left, right) -> left.addAll(right.build()),
            (Function<ImmutableList.Builder<T>, ImmutableList<T>>) ImmutableList.Builder::build);
    }

This still gives an error on ImmutableList.Builder::add:

    "Cannot make a static reference to the non-static method add(Object[]) from the type
     ImmutableList.Builder"

I tried isolating that one piece of the code and yes, it still happens on this one-liner:

    BiConsumer<ImmutableList.Builder<T>, T> accumulator = ImmutableList.Builder::add;

So it seems that method references to non-static methods are perhaps not being resolved correctly. It's picking add(Object[]) when add(Object) exists as well and would probably have worked.

This occurs on v4.4.1 as well as Mars build N20141206-2000.