Fix #492. Traits that require an outer pointer are not SAMs.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/transform/ExplicitOuter.scala b/src/dotty/tools/dotc/transform/ExplicitOuter.scala
index 8baaa3a11..9fc164d3b 100644
--- a/src/dotty/tools/dotc/transform/ExplicitOuter.scala
+++ b/src/dotty/tools/dotc/transform/ExplicitOuter.scala
@@ -13,6 +13,7 @@ import core.Names._
 import core.NameOps._
 import ast.Trees._
 import SymUtils._
+import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.core.Phases.Phase
 import util.Attachment
 import collection.mutable
@@ -102,6 +103,15 @@ class ExplicitOuter extends MiniPhaseTransform with InfoTransformer { thisTransf
     }
     else impl
   }
+
+  override def transformClosure(tree: Closure)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
+    if (tree.tpt ne EmptyTree) {
+      val cls = tree.tpt.asInstanceOf[TypeTree].tpe.classSymbol
+      if (cls.exists && hasOuter(cls.asClass))
+        ctx.error("Not a single abstract method type, requires an outer pointer", tree.pos)
+    }
+    tree
+  }
 }
 
 object ExplicitOuter {