New phase: ElimErasedValueType

This phase erases ErasedValueType to their underlying type, in scalac
this was done in PostErasure.

Author: smarter

src/dotty/tools/dotc/Compiler.scala

@@ -57,7 +57,8 @@ class Compiler {
            new ElimByName,
            new ResolveSuper),
       List(new Erasure),
-      List(new Mixin,
+      List(new ElimErasedValueType,
+           new Mixin,
            new Memoize,
            new CapturedVars,
            new Constructors,

src/dotty/tools/dotc/transform/ElimErasedValueType.scala

@@ -0,0 +1,82 @@
+package dotty.tools.dotc
+package transform
+
+import ast.{Trees, tpd}
+import core._, core.Decorators._
+import TreeTransforms._, Phases.Phase
+import Types._, Contexts._, Constants._, Names._, NameOps._, Flags._, DenotTransformers._
+import SymDenotations._, Symbols._, StdNames._, Annotations._, Trees._, Scopes._, Denotations._
+import TypeErasure.ErasedValueType, ValueClasses._
+
+/** This phase erases ErasedValueType to their underlying type.
+ *  It also removes the synthetic cast methods u2evt$ and evt2u$ which are
+ *  no longer needed afterwards.
+ */
+class ElimErasedValueType extends MiniPhaseTransform with InfoTransformer {
+
+  import tpd._
+
+  override def phaseName: String = "elimErasedValueType"
+
+  override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Erasure])
+
+  def transformInfo(tp: Type, sym: Symbol)(implicit ctx: Context): Type = sym match {
+    case sym: ClassSymbol if sym is ModuleClass =>
+      sym.companionClass match {
+        case origClass: ClassSymbol if isDerivedValueClass(origClass) =>
+          val cinfo = tp.asInstanceOf[ClassInfo]
+          val decls1 = cinfo.decls.cloneScope
+          ctx.atPhase(this.next) { implicit ctx =>
+            // Remove synthetic cast methods introduced by ExtensionMethods,
+            // they are no longer needed after this phase.
+            decls1.unlink(cinfo.decl(nme.U2EVT).symbol)
+            decls1.unlink(cinfo.decl(nme.EVT2U).symbol)
+          }
+          cinfo.derivedClassInfo(decls = decls1)
+        case _ =>
+          tp
+      }
+    case _ =>
+      elimEVT(tp)
+  }
+
+  def elimEVT(tp: Type)(implicit ctx: Context): Type = tp match {
+    case ErasedValueType(_, underlying) =>
+      elimEVT(underlying)
+    case tp: MethodType =>
+      val paramTypes = tp.paramTypes.mapConserve(elimEVT)
+      val retType = elimEVT(tp.resultType)
+      tp.derivedMethodType(tp.paramNames, paramTypes, retType)
+    case _ =>
+      tp
+  }
+
+  def transformTypeOfTree(tree: Tree)(implicit ctx: Context): Tree =
+    tree.withType(elimEVT(tree.tpe))
+
+  override def transformApply(tree: Apply)(implicit ctx: Context, info: TransformerInfo): Tree = {
+    val Apply(fun, args) = tree
+    val name = fun.symbol.name
+
+    // The casts to and from ErasedValueType are no longer needed once ErasedValueType
+    // has been eliminated.
+    val t =
+      if ((name eq nme.U2EVT) || (name eq nme.EVT2U))
+        args.head
+      else
+        tree
+    transformTypeOfTree(t)
+  }
+
+  // FIXME: transformIf and transformBlock won't be required anymore once #444 is fixed.
+  override def transformIdent(tree: Ident)(implicit ctx: Context, info: TransformerInfo): Tree =
+    transformTypeOfTree(tree)
+  override def transformSelect(tree: Select)(implicit ctx: Context, info: TransformerInfo): Tree =
+    transformTypeOfTree(tree)
+  override def transformBlock(tree: Block)(implicit ctx: Context, info: TransformerInfo): Tree =
+    transformTypeOfTree(tree)
+  override def transformIf(tree: If)(implicit ctx: Context, info: TransformerInfo): Tree =
+    transformTypeOfTree(tree)
+  override def transformTypeTree(tree: TypeTree)(implicit ctx: Context, info: TransformerInfo): Tree =
+    transformTypeOfTree(tree)
+}