New phase trait constructors.

Renames constructors in traits so that backend will call them with invokeInterface, instead of invokeSpecial
 Also makes sure that renamed constructor bodies conforms to type of method

Author: DarkDimius

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, new ElimWildcardIdents),
+      List(/*new PrivateToStatic,*/ new CollectEntryPoints, new LabelDefs, new ElimWildcardIdents, new TraitConstructors),
       List(new GenBCode)
     )
 

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

@@ -0,0 +1,37 @@
+package dotty.tools.dotc.transform
+
+import dotty.tools.dotc.ast.tpd
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.DenotTransformers.{SymTransformer, DenotTransformer}
+import dotty.tools.dotc.core.Denotations.SingleDenotation
+import dotty.tools.dotc.core.Phases.Phase
+import dotty.tools.dotc.core.StdNames._
+import dotty.tools.dotc.core.SymDenotations.SymDenotation
+import dotty.tools.dotc.core._
+import dotty.tools.dotc.transform.TreeTransforms.{MiniPhaseTransform, TransformerInfo}
+
+/***
+  * Renames constructors in traits so that backend will call them with invokeInterface
+  * Also makes sure that renamed constructor bodies conforms to type of method
+ */
+class TraitConstructors extends MiniPhaseTransform with SymTransformer {
+  import dotty.tools.dotc.ast.tpd._
+  def phaseName: String = "traitConstructors"
+
+
+  override def treeTransformPhase: Phase = this.phase
+
+  def transformSym(sym: SymDenotation)(implicit ctx: Context): SymDenotation = {
+    if(sym.isPrimaryConstructor && (sym.owner is Flags.Trait))
+      sym.copySymDenotation(name = nme.INITIALIZER_PREFIX ++ sym.owner.fullName)
+    else sym
+  }
+
+  override def transformDefDef(tree: tpd.DefDef)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
+    val sym = tree.symbol
+    if (sym.isPrimaryConstructor && (sym.owner is Flags.Trait))
+      cpy.DefDef(tree)(rhs = Block(List(tree.rhs), This(tree.symbol.enclosingClass.asClass)))
+    else tree
+  }
+
+}