2 files changed, 50 insertions, 1 deletions
diff --git a/src/dotty/tools/dotc/Compiler.scala b/src/dotty/tools/dotc/Compiler.scala
index cb758c002..e8df49008 100644
--- a/src/dotty/tools/dotc/Compiler.scala
+++ b/src/dotty/tools/dotc/Compiler.scala
@@ -67,7 +67,7 @@ class Compiler {
       List(new LambdaLift,
            new Flatten,
            new RestoreScopes),
-      List(/*new PrivateToStatic,*/ new CollectEntryPoints, new LabelDefs),
+      List(/*new PrivateToStatic,*/ new CollectEntryPoints, new LabelDefs, new ElimWildcardIdents),
       List(new GenBCode)
     )
 
diff --git a/src/dotty/tools/dotc/transform/ElimWildcardIdents.scala b/src/dotty/tools/dotc/transform/ElimWildcardIdents.scala
new file mode 100644
index 000000000..5ef0dfe84
--- /dev/null
+++ b/src/dotty/tools/dotc/transform/ElimWildcardIdents.scala
@@ -0,0 +1,49 @@
+package dotty.tools.dotc.transform
+
+import dotty.tools.dotc.transform.TreeTransforms.{TransformerInfo, TreeTransform, TreeTransformer, MiniPhaseTransform}
+import dotty.tools.dotc.ast.{untpd, tpd}
+import dotty.tools.dotc.core.Contexts.Context
+import scala.collection.mutable.ListBuffer
+import dotty.tools.dotc.core.{Scopes, Flags}
+import dotty.tools.dotc.core.Symbols.NoSymbol
+import scala.annotation.tailrec
+import dotty.tools.dotc.core._
+import Symbols._
+import scala.Some
+import dotty.tools.dotc.transform.TreeTransforms.{NXTransformations, TransformerInfo, TreeTransform, TreeTransformer}
+import dotty.tools.dotc.core.Contexts.Context
+import scala.collection.mutable
+import dotty.tools.dotc.core.Names.Name
+import NameOps._
+import Types._
+import scala.collection.SortedSet
+import Decorators._
+import StdNames._
+import dotty.tools.dotc.util.Positions.Position
+import dotty.tools.dotc.config.JavaPlatform
+
+/**
+ * Replace Ident("_") in tree with default values of corresponding type:
+ *   numerics: `0`
+ *   booleans: `false`
+ *   classes: `null`
+ */
+class ElimWildcardIdents extends MiniPhaseTransform {
+  import tpd._
+  def phaseName: String = "elimWildcardIdents"
+
+
+  override def transformDefDef(tree: tpd.DefDef)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
+    def stripBlocks(arg: Tree): Tree =  arg match {
+      case b: Block if b.stats.isEmpty => stripBlocks(b.expr)
+      case _ => arg
+    }
+    val b = stripBlocks(tree.rhs)
+    b match {
+      case x: Ident if (x.name == nme.WILDCARD && x.symbol.isClass) =>
+        tpd.DefDef(tree.symbol.asTerm, tpd.initValue(x.tpe))
+      case _ => tree
+    }
+  }
+
+}