introduces global.pendingSuperCall

Similarly to global.emptyValDef, which is a dummy that stands for an
empty self-type, this commit introduces global.pendingSuperCall, which
stands for a yet-to-be-filled-in call to a superclass constructor.

pendingSuperCall is emitted by Parsers.template, treated specially by
Typers.typedParentType and replaced with a real superclass ctor call
by Typers.typedTemplate.

To avoid copy/paste, this commit also factors out and unifies dumminess
of EmptyTree, emptyValDef and pendingSuperCall - they all don't have a
position and actively refuse to gain one, same story for tpe.

8 files changed, 27 insertions, 15 deletions

diff --git a/src/reflect/scala/reflect/api/BuildUtils.scala b/src/reflect/scala/reflect/api/BuildUtils.scala
index 0c8e81a220..8f256aa1f5 100644
--- a/src/reflect/scala/reflect/api/BuildUtils.scala
+++ b/src/reflect/scala/reflect/api/BuildUtils.scala
@@ -59,8 +59,6 @@ private[reflect] trait BuildUtils { self: Universe =>
 
     def flagsFromBits(bits: Long): FlagSet
 
-    def emptyValDef: ValDef
-
     def This(sym: Symbol): Tree
 
     def Select(qualifier: Tree, sym: Symbol): Select
diff --git a/src/reflect/scala/reflect/api/Trees.scala b/src/reflect/scala/reflect/api/Trees.scala
index c98107f9b5..9a65ddaa96 100644
--- a/src/reflect/scala/reflect/api/Trees.scala
+++ b/src/reflect/scala/reflect/api/Trees.scala
@@ -2366,6 +2366,15 @@ trait Trees { self: Universe =>
    */
   val emptyValDef: ValDef
 
+  /** An empty superclass constructor call corresponding to:
+   *    super.<init>()
+   *  This is used as a placeholder in the primary constructor body in class templates
+   *  to denote the insertion point of a call to superclass constructor after the typechecker
+   *  figures out the superclass of a given template.
+   *  @group Trees
+   */
+  val pendingSuperCall: Apply
+
 // ---------------------- factories ----------------------------------------------
 
   /** A factory method for `ClassDef` nodes.
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index 9f41f0336e..b1b0c5b60b 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -47,8 +47,6 @@ trait BuildUtils { self: SymbolTable =>
 
     def flagsFromBits(bits: Long): FlagSet = bits
 
-    def emptyValDef: ValDef = self.emptyValDef
-
     def This(sym: Symbol): Tree = self.This(sym)
 
     def Select(qualifier: Tree, sym: Symbol): Select = self.Select(qualifier, sym)
diff --git a/src/reflect/scala/reflect/internal/Importers.scala b/src/reflect/scala/reflect/internal/Importers.scala
index 43902c1930..2f2b02975c 100644
--- a/src/reflect/scala/reflect/internal/Importers.scala
+++ b/src/reflect/scala/reflect/internal/Importers.scala
@@ -334,6 +334,8 @@ trait Importers extends api.Importers { self: SymbolTable =>
           new ModuleDef(importModifiers(mods), importName(name).toTermName, importTemplate(impl))
         case from.emptyValDef =>
           emptyValDef
+        case from.pendingSuperCall =>
+          pendingSuperCall
         case from.ValDef(mods, name, tpt, rhs) =>
           new ValDef(importModifiers(mods), importName(name).toTermName, importTree(tpt), importTree(rhs))
         case from.DefDef(mods, name, tparams, vparamss, tpt, rhs) =>
diff --git a/src/reflect/scala/reflect/internal/Positions.scala b/src/reflect/scala/reflect/internal/Positions.scala
index faa161d6b1..b65df0e70b 100644
--- a/src/reflect/scala/reflect/internal/Positions.scala
+++ b/src/reflect/scala/reflect/internal/Positions.scala
@@ -38,7 +38,7 @@ trait Positions extends api.Positions { self: SymbolTable =>
   protected class DefaultPosAssigner extends PosAssigner {
     var pos: Position = _
     override def traverse(t: Tree) {
-      if (t eq EmptyTree) ()
+      if (t.isDummy) ()
       else if (t.pos == NoPosition) {
         t.setPos(pos)
         super.traverse(t)   // TODO: bug? shouldn't the traverse be outside of the if?
diff --git a/src/reflect/scala/reflect/internal/Printers.scala b/src/reflect/scala/reflect/internal/Printers.scala
index 80d247c0ea..6f834803c4 100644
--- a/src/reflect/scala/reflect/internal/Printers.scala
+++ b/src/reflect/scala/reflect/internal/Printers.scala
@@ -542,8 +542,10 @@ trait Printers extends api.Printers { self: SymbolTable =>
           print(")")
         case EmptyTree =>
           print("EmptyTree")
-        case emptyValDef: AnyRef if emptyValDef eq self.emptyValDef =>
+        case self.emptyValDef =>
           print("emptyValDef")
+        case self.pendingSuperCall =>
+          print("pendingSuperCall")
         case tree: Tree =>
           val hasSymbol = tree.hasSymbol && tree.symbol != NoSymbol
           val isError = hasSymbol && tree.symbol.name.toString == nme.ERROR.toString
diff --git a/src/reflect/scala/reflect/internal/StdNames.scala b/src/reflect/scala/reflect/internal/StdNames.scala
index 5e7f5777b2..c870d8972d 100644
--- a/src/reflect/scala/reflect/internal/StdNames.scala
+++ b/src/reflect/scala/reflect/internal/StdNames.scala
@@ -730,6 +730,7 @@ trait StdNames {
     val null_ : NameType               = "null"
     val ofDim: NameType                = "ofDim"
     val origin: NameType               = "origin"
+    val pendingSuperCall: NameType     = "pendingSuperCall"
     val prefix : NameType              = "prefix"
     val productArity: NameType         = "productArity"
     val productElement: NameType       = "productElement"
diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 0087bb93e7..047298cf82 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -36,6 +36,7 @@ trait Trees extends api.Trees { self: SymbolTable =>
     def isDef = false
 
     def isEmpty = false
+    def isDummy = false
 
     /** The canonical way to test if a Tree represents a term.
      */
@@ -228,14 +229,6 @@ trait Trees extends api.Trees { self: SymbolTable =>
     override def isDef = true
   }
 
-  case object EmptyTree extends TermTree {
-    val asList = List(this)
-    super.tpe_=(NoType)
-    override def tpe_=(t: Type) =
-      if (t != NoType) throw new UnsupportedOperationException("tpe_=("+t+") inapplicable for <empty>")
-    override def isEmpty = true
-  }
-
   abstract class MemberDef extends DefTree with MemberDefApi {
     def mods: Modifiers
     def keyword: String = this match {
@@ -599,6 +592,7 @@ trait Trees extends api.Trees { self: SymbolTable =>
         case _: ApplyToImplicitArgs => new ApplyToImplicitArgs(fun, args)
         case _: ApplyImplicitView => new ApplyImplicitView(fun, args)
         // TODO: ApplyConstructor ???
+        case self.pendingSuperCall => self.pendingSuperCall
         case _ => new Apply(fun, args)
       }).copyAttrs(tree)
     def ApplyDynamic(tree: Tree, qual: Tree, args: List[Tree]) =
@@ -961,12 +955,20 @@ trait Trees extends api.Trees { self: SymbolTable =>
 
   def ValDef(sym: Symbol): ValDef = ValDef(sym, EmptyTree)
 
-  object emptyValDef extends ValDef(Modifiers(PRIVATE), nme.WILDCARD, TypeTree(NoType), EmptyTree) {
+  trait DummyTree extends Tree {
     override def isEmpty = true
+    override def isDummy = true
     super.setPos(NoPosition)
     override def setPos(pos: Position) = { assert(false); this }
+    super.setType(NoType)
+    override def tpe_=(t: Type) =
+      if (t != NoType) throw new UnsupportedOperationException("tpe_=("+t+") inapplicable for "+self.toString)
   }
 
+  case object EmptyTree extends TermTree with DummyTree { val asList = List(this) }
+  object emptyValDef extends ValDef(Modifiers(PRIVATE), nme.WILDCARD, TypeTree(NoType), EmptyTree) with DummyTree
+  object pendingSuperCall extends Apply(Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR), List()) with DummyTree
+
   def DefDef(sym: Symbol, mods: Modifiers, vparamss: List[List[ValDef]], rhs: Tree): DefDef =
     atPos(sym.pos) {
       assert(sym != NoSymbol)