tree eb87961ff032167d5997c055e797e83e217136b8
parent db4dbfd4df8a4394de71c946e6e143ff5dcb26c5
author sameb <sameb@google.com> 1424819501 -0800
committer Sam Berlin <sameb@google.com> 1424820510 -0500

Further fixes for https://github.com/google/guice/issues/904 -- java8 generates
default methods for subclasses when they override generic methods with the more
specific type.

We use a two-tiered approach to fixing: (1) try to use MethodHandles + unreflectSpecial, which lets us call default method implementations directly, and if that doesn't work then (2) try to map default methods to compatible method signatures that could be the overrides of the method.  (1) may not always work because we're using a private API [new Lookup(clazz, int)], but we need to do that in order to non-public classes.  (2) may not always work because it's possible to have more than one compatible method signature.

In the unlikely case that both (1) & (2) fail, we give an error message.
Also: we must validate the default method's return type for visibility vs the factory type's visibility too.

This ends up with two possible differences caused by java8:
a) If the Lookup cxtor can't be used (different JDK, version skew, etc..) and there's more than one compatible method signature: we fail.
b) If the default method's return type isn't public but the factory is public: we fail.

For reference, javac8 generates a default method in the following scenario:
interface Parent<I extends CharSequence, O extends Number> {
O create(I input);
}
interface Child<String, Integer> {
Integer create(String input);
}

Child has a generated default method of:
Number create(CharSequence input);

... so, for example, failure could be newly triggered if 'Number' was package-private but Child was public, or if the reflection APIs didn't work and Child also had a 'Integer create(StringBuilder input);' method.
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