Fix handling of default argument in curried supercalls

Default arguments in a parameter list of a supercall that follows
the first one were sometimes handled incorrectly. In this case,
the supercall can a block which contains bindings of earlier arguments
that are passed to the default getter.

Author: odersky

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -85,6 +85,12 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
     case _ => tree
   }
 
+  /** If this is a block, its expression part */
+  def stripBlock(tree: Tree): Tree = unsplice(tree) match {
+    case Block(_, expr) => stripBlock(expr)
+    case _ => tree
+  }
+
   /** The number of arguments in an application */
   def numArgs(tree: Tree): Int = unsplice(tree) match {
     case Apply(fn, args) => numArgs(fn) + args.length

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

@@ -168,15 +168,19 @@ class Mixin extends MiniPhase with SymTransformer { thisPhase =>
      *  to be used as initializers of trait parameters if the target of the call
      *  is a trait.
      */
-    def transformConstructor(tree: Tree): (Tree, List[Tree]) = {
-      val Apply(sel @ Select(New(_), nme.CONSTRUCTOR), args) = tree
-      val (callArgs, initArgs) = if (tree.symbol.owner.is(Trait)) (Nil, args) else (args, Nil)
-      (superRef(tree.symbol, tree.pos).appliedToArgs(callArgs), initArgs)
+    def transformConstructor(tree: Tree): (Tree, List[Tree]) = tree match {
+      case Block(stats, expr) =>
+        val (scall, inits) = transformConstructor(expr)
+        (cpy.Block(tree)(stats, scall), inits)
+      case _ =>
+        val Apply(sel @ Select(New(_), nme.CONSTRUCTOR), args) = tree
+        val (callArgs, initArgs) = if (tree.symbol.owner.is(Trait)) (Nil, args) else (args, Nil)
+        (superRef(tree.symbol, tree.pos).appliedToArgs(callArgs), initArgs)
     }
 
     val superCallsAndArgs = (
-      for (p <- impl.parents if p.symbol.isConstructor)
-      yield p.symbol.owner -> transformConstructor(p)
+      for (p <- impl.parents; constr = stripBlock(p).symbol if constr.isConstructor)
+      yield constr.owner -> transformConstructor(p)
     ).toMap
     val superCalls = superCallsAndArgs.mapValues(_._1)
     val initArgs = superCallsAndArgs.mapValues(_._2)

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -402,7 +402,7 @@ object ProtoTypes {
   }
 
   class UnapplyFunProto(argType: Type, typer: Typer)(implicit ctx: Context) extends FunProto(
-    untpd.TypedSplice(dummyTreeOfType(argType))(ctx) :: Nil, WildcardType)(typer, new FunProtoState()) // TODO: Investigate Dotty failure with default param
+    untpd.TypedSplice(dummyTreeOfType(argType))(ctx) :: Nil, WildcardType)(typer)
 
   /** A prototype for expressions [] that are type-parameterized:
    *

tests/pos/default-super.scala

@@ -0,0 +1,8 @@
+class A(x: Int)(y: String = "hi")
+
+object Test {
+  def f() = 22
+
+  class B extends A(f())()
+
+}