Commits on Jul 22, 2020

1. Create a new multibinder alternate for Set<? extends T> …

   This is a simple linked binding to the original multibinder set. This is
   safe because 'Set<? extends T>' is assignable from 'Set<T>'.
   
   This is useful for projects integrating Guice and Kotlin. In Kotlin there
   are different types for read-only vs. read-write Sets. When declaring a
   read-only Set, the bytecode includes a wildcard.
   
   In particular, this Kotlin:
   
       var setA: Set<Runnable>
       var setB: MutableSet<Runnable>
   
   is equivalent to this Java:
   
       Set<? extends Runnable> setA;
       Set<Runnable> setB;
   
   Using Kotlin with Guice multibindings is quite annoying because the binding
   to `Set<Runnable>` is typically provided, but `Set<? extends Runnable>` is
   needed.
   
   The typical Kotlin workaround is also ugly:
   
       var setA: Set<@JvmSuppressWildcards Runnable>
   
   With this fix, Guice multibindings and Guice should just work.
   
   I expect this may be backwards-incompatible with a very small number of Kotlin
   applications that implement a different workaround to the above problem:
   
       @provides
       Set<? extends Runnable> provideRunnables(Set<Runnable> set) {
         return set;
       }
   
   I don't expect backwards incompatibility with Java programs. In such programs
   the behavior change will result in a fast failure (injector fails to create)
   which is easy to diagnose and fix.

   

   swankjesse committed Jul 22, 2020
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