Relax erased type check

Now that mixin forwarders are generated after erasure, we may end up
with a reference to ThisType(*:) after erasure in Tuple.scala,
because *: extends NonEmptyTuple which erases to Product, and Product
has methods that should get mixin forwarders.

This fixes the tastyBootstrap test broken after the last commit.

Author: smarter

compiler/src/dotty/tools/dotc/transform/Erasure.scala

@@ -134,13 +134,17 @@ class Erasure extends Phase with DenotTransformer {
   }
 
   def assertErased(tp: Type, tree: tpd.Tree = tpd.EmptyTree)(implicit ctx: Context): Unit = {
-    def isAllowed(cls: Symbol, sourceName: String) =
-      tp.typeSymbol == cls && ctx.compilationUnit.source.file.name == sourceName
+    def isAllowed(tp: Type, cls: Symbol, sourceName: String): Boolean = tp match {
+      case tp: ThisType =>
+        isAllowed(tp.underlying, cls, sourceName)
+      case _ =>
+        tp.typeSymbol == cls && ctx.compilationUnit.source.file.name == sourceName
+    }
     assert(isErasedType(tp) ||
-           isAllowed(defn.ArrayClass, "Array.scala") ||
-           isAllowed(defn.TupleClass, "Tuple.scala") ||
-           isAllowed(defn.NonEmptyTupleClass, "Tuple.scala") ||
-           isAllowed(defn.PairClass, "Tuple.scala"),
+           isAllowed(tp, defn.ArrayClass, "Array.scala") ||
+           isAllowed(tp, defn.TupleClass, "Tuple.scala") ||
+           isAllowed(tp, defn.NonEmptyTupleClass, "Tuple.scala") ||
+           isAllowed(tp, defn.PairClass, "Tuple.scala"),
         i"The type $tp - ${tp.toString} of class ${tp.getClass} of tree $tree : ${tree.tpe} / ${tree.getClass} is illegal after erasure, phase = ${ctx.phase.prev}")
   }
 }