Fix treatment of by name functions

By-name functions like `(=> T) => T` were not treated correctly before.
Witness the disabled `-Ycheck:gettersSetters` for transform/TreeCheckers
in thge test suite. This commit changes the scheme how => T types are treated
and fixes the problems with by-name functions.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/TypeErasure.scala b/src/dotty/tools/dotc/TypeErasure.scala
index 851be7658..2a55d6732 100644
--- a/src/dotty/tools/dotc/TypeErasure.scala
+++ b/src/dotty/tools/dotc/TypeErasure.scala
@@ -111,6 +111,12 @@ object TypeErasure {
       erasure(tp)
   }
 
+  /** The erasure of a symbol's info. This is different of `erasure` in the way `ExprType`s are
+   *  treated. `eraseInfo` maps them them to nullary method types, whereas `erasure` maps them
+   *  to `Function0`.
+   */
+  def eraseInfo(tp: Type)(implicit ctx: Context): Type = scalaErasureFn.eraseInfo(tp)(erasureCtx)
+
   /** The erasure of a function result type. Differs from normal erasure in that
    *  Unit is kept instead of being mapped to BoxedUnit.
    */
@@ -135,7 +141,7 @@ object TypeErasure {
     if ((sym eq defn.Any_asInstanceOf) || (sym eq defn.Any_isInstanceOf)) eraseParamBounds(sym.info.asInstanceOf[PolyType])
     else if (sym.isAbstractType) TypeAlias(WildcardType)
     else if (sym.isConstructor) outer.addParam(sym.owner.asClass, erase(tp)(erasureCtx))
-    else erase(tp)(erasureCtx)
+    else eraseInfo(tp)(erasureCtx)
   }
 
   def isUnboundedGeneric(tp: Type)(implicit ctx: Context) = !(
@@ -263,7 +269,7 @@ class TypeErasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wild
     case SuperType(thistpe, supertpe) =>
       SuperType(this(thistpe), this(supertpe))
     case ExprType(rt) =>
-      MethodType(Nil, Nil, this(rt))
+      defn.FunctionClass(0).typeRef
     case tp: TypeProxy =>
       this(tp.underlying)
     case AndType(tp1, tp2) =>
@@ -312,6 +318,11 @@ class TypeErasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wild
     else JavaArrayType(this(elemtp))
   }
 
+  def eraseInfo(tp: Type)(implicit ctx: Context) = tp match {
+    case ExprType(rt) => MethodType(Nil, Nil, erasure(rt))
+    case tp => erasure(tp)
+  }
+
   private def eraseDerivedValueClassRef(tref: TypeRef)(implicit ctx: Context): Type =
     unsupported("eraseDerivedValueClass")