Closes #4047. Review by odersky

3 files changed, 47 insertions, 5 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Erasure.scala b/src/compiler/scala/tools/nsc/transform/Erasure.scala
index 1df0b5bf3b..1a97c1f6c9 100644
--- a/src/compiler/scala/tools/nsc/transform/Erasure.scala
+++ b/src/compiler/scala/tools/nsc/transform/Erasure.scala
@@ -449,7 +449,10 @@ abstract class Erasure extends AddInterfaces with typechecker.Analyzer with ast.
       case _ =>
         typedPos(tree.pos)(tree.tpe.typeSymbol match {
           case UnitClass  =>
-            if (treeInfo isPureExpr tree) REF(BoxedUnit_UNIT)
+            // Although lazy vals are pure expressions,
+            // we should still call them in bridge methods
+            if (treeInfo.isPureExpr(tree) && (tree.symbol == null || !tree.symbol.isLazy))
+              REF(BoxedUnit_UNIT)
             else BLOCK(tree, REF(BoxedUnit_UNIT))
           case x          =>
             assert(x != ArrayClass)
@@ -818,15 +821,15 @@ abstract class Erasure extends AddInterfaces with typechecker.Analyzer with ast.
       while (opc.hasNext) {
         val member = opc.overriding
         val other = opc.overridden
-        //Console.println("bridge? " + member + ":" + member.tpe + member.locationString + " to " + other + ":" + other.tpe + other.locationString);//DEBUG
+        //Console.println("bridge? " + member + ":" + member.tpe + member.locationString + " to " + other + ":" + other.tpe + other.locationString)//DEBUG
         if (atPhase(currentRun.explicitouterPhase)(!member.isDeferred)) {
-          val otpe = erasure(other.tpe);
+          val otpe = erasure(other.tpe)
           val bridgeNeeded = atPhase(phase.next) (
             !(other.tpe =:= member.tpe) &&
             !(deconstMap(other.tpe) =:= deconstMap(member.tpe)) &&
             { var e = bridgesScope.lookupEntry(member.name)
               while ((e ne null) && !((e.sym.tpe =:= otpe) && (bridgeTarget(e.sym) == member)))
-                e = bridgesScope.lookupNextEntry(e);
+                e = bridgesScope.lookupNextEntry(e)
               (e eq null)
             }
           );
@@ -860,7 +863,7 @@ abstract class Erasure extends AddInterfaces with typechecker.Analyzer with ast.
                     log("generating bridge from " + other + "(" + Flags.flagsToString(bridge.flags)  + ")" + ":" + otpe + other.locationString + " to " + member + ":" + erasure(member.tpe) + member.locationString + " =\n " + bridgeDef);
                   bridgeDef
                 }
-              } :: bridges;
+              } :: bridges
           }
         }
         opc.next
diff --git a/test/files/run/t4047.check b/test/files/run/t4047.check
new file mode 100644
index 0000000000..2a942a70e0
--- /dev/null
+++ b/test/files/run/t4047.check
@@ -0,0 +1,5 @@
+Unit: called A.foo
+Unit: called B.foo
+Unit: called C.foo
+Unit: called D.foo
+Unit: called D.foo
diff --git a/test/files/run/t4047.scala b/test/files/run/t4047.scala
new file mode 100644
index 0000000000..cd42a8b4df
--- /dev/null
+++ b/test/files/run/t4047.scala
@@ -0,0 +1,34 @@
+trait Foo[T] { val foo: T}
+
+class A extends Foo[Unit]{
+  lazy val foo = println("Unit: called A.foo")
+}
+
+class B extends Foo[Unit]{
+  val foo = println("Unit: called B.foo")
+}
+
+trait Bar[T] { def foo: T}
+
+class C extends Bar[Unit]{
+  lazy val foo = println("Unit: called C.foo")
+}
+
+class D extends Bar[Unit]{
+  def foo = println("Unit: called D.foo")
+}
+
+object Test extends Application {
+  val a: Foo[Unit] = new A
+  a.foo
+  a.foo
+  val b: Foo[Unit] = new B
+  b.foo
+  b.foo
+  val c: Bar[Unit] = new C
+  c.foo
+  c.foo
+  val d: Bar[Unit] = new D
+  d.foo
+  d.foo
+}