New phase: LinkScala2ImplClasses

This phase rewrites supercalls to calls to static implementation class methods.

Author: odersky

src/dotty/tools/dotc/Compiler.scala

@@ -64,7 +64,7 @@ class Compiler {
            new Mixin,
            new LazyVals,
            new Memoize,
-           //new LinkScala2ImplClasses,
+           new LinkScala2ImplClasses,
            new CapturedVars, // capturedVars has a transformUnit: no phases should introduce local mutable vars here
            new Constructors,
            new FunctionalInterfaces),

src/dotty/tools/dotc/transform/LinkScala2ImplClasses.scala

@@ -0,0 +1,58 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import TreeTransforms._
+import Contexts.Context
+import Flags._
+import SymUtils._
+import Symbols._
+import SymDenotations._
+import Types._
+import Decorators._
+import DenotTransformers._
+import StdNames._
+import NameOps._
+import Phases._
+import ast.untpd
+import ast.Trees._
+import collection.mutable
+
+/** Rewrite calls
+ *
+ *    super[M].f(args)
+ *
+ *  where M is a Scala2 trait implemented by the current class to
+ *
+ *    M$class.f(this, args)
+ *
+ *  provided the implementation class M$class defines a corresponding function `f`.
+ */
+class LinkScala2ImplClasses extends MiniPhaseTransform with IdentityDenotTransformer { thisTransform =>
+  import ast.tpd._
+
+  override def phaseName: String = "linkScala2ImplClasses"
+
+  override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Mixin])
+
+  override def transformApply(app: Apply)(implicit ctx: Context, info: TransformerInfo) = {
+    def currentClass = ctx.owner.enclosingClass.asClass
+    app match {
+      case Apply(sel @ Select(Super(_, _), _), args)
+      if sel.symbol.owner.is(Scala2xTrait) && currentClass.mixins.contains(sel.symbol.owner) =>
+        val impl = implMethod(sel.symbol)
+        if (impl.exists) Apply(ref(impl), This(currentClass) :: args).withPos(app.pos)
+        else app // could have been an abstract method in a trait linked to from a super constructor
+      case _ =>
+        app
+    }
+  }
+
+  private def implMethod(meth: Symbol)(implicit ctx: Context): Symbol =
+    meth.owner.implClass.info
+      .decl(if (meth.isConstructor) nme.IMPLCLASS_CONSTRUCTOR else meth.name)
+      .suchThat(c => FullParameterization.memberSignature(c.info) == meth.signature)
+      .symbol
+
+  private val Scala2xTrait = allOf(Scala2x, Trait)
+}