SI-6199 unit-returning methods now return unit

Since Scala reflection relies on Java reflection to perform member invocations,
it inherits some of the quirks of the underlying platform.

One of such quirks is returning null when invoking a void-returning method.
This is now fixed by introducing a check after calling invoke.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/runtime/JavaMirrors.scala b/src/reflect/scala/reflect/runtime/JavaMirrors.scala
index d671225c37..e48c933584 100644
--- a/src/reflect/scala/reflect/runtime/JavaMirrors.scala
+++ b/src/reflect/scala/reflect/runtime/JavaMirrors.scala
@@ -280,19 +280,25 @@ trait JavaMirrors extends internal.SymbolTable with api.JavaUniverse { self: Sym
         jmeth
       }
 
+      def jinvoke(jmeth: jMethod, receiver: Any, args: Seq[Any]): Any = {
+        val result = jmeth.invoke(receiver, args.asInstanceOf[Seq[AnyRef]]: _*)
+        if (jmeth.getReturnType == java.lang.Void.TYPE) ()
+        else result
+      }
+
       override def toString = s"method mirror for ${showMethodSig(symbol)} (bound to $receiver)"
     }
 
     private class JavaVanillaMethodMirror(val receiver: Any, symbol: MethodSymbol)
             extends JavaMethodMirror(symbol) {
-      def apply(args: Any*): Any = jmeth.invoke(receiver, args.asInstanceOf[Seq[AnyRef]]: _*)
+      def apply(args: Any*): Any = jinvoke(jmeth, receiver, args)
     }
 
     private class JavaByNameMethodMirror(val receiver: Any, symbol: MethodSymbol)
             extends JavaMethodMirror(symbol) {
       def apply(args: Any*): Any = {
         val transformed = map2(args.toList, symbol.params.flatten)((arg, param) => if (isByNameParamType(param.info)) () => arg else arg)
-        jmeth.invoke(receiver, transformed.asInstanceOf[Seq[AnyRef]]: _*)
+        jinvoke(jmeth, receiver, transformed)
       }
     }
 
@@ -321,7 +327,7 @@ trait JavaMirrors extends internal.SymbolTable with api.JavaUniverse { self: Sym
         def invokeMagicPrimitiveMethod = {
           val jmeths = classOf[BoxesRunTime].getDeclaredMethods.filter(_.getName == nme.primitiveMethodName(symbol.name).toString)
           assert(jmeths.length == 1, jmeths.toList)
-          jmeths.head.invoke(null, (objReceiver +: objArgs): _*)
+          jinvoke(jmeths.head, null, objReceiver +: objArgs)
         }
 
         symbol match {