refactors handling of parent types

At the moment parser does too much w.r.t handling of parent types.
It checks whether a parent can have value arguments or not and
more importantly, it synthesizes constructors and super calls.

This approach is fundamentally incompatible with upcoming type macros.
Take for example the following two snippets of code:

  `class C extends A(2)`
  `class D extends A(2) with B(3)`

In the first snippet, `A` might be a type macro, therefore the super call
`A.super(2)` eagerly emitted by the parser might be meaningless. In the
second snippet parser will report an error despite that `B` might be
a type macro which expands into a trait.

Unfortunately we cannot simply augment the parser with the `isTypeMacro`
check. This is because to find out whether an identifier refers to a type
macro, one needs to perform a typecheck, which the parser cannot do.

Therefore we need a deep change in how parent types and constructors
are processed by the compiler, which is implemented in this commit.

1 files changed, 12 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/Trees.scala b/src/compiler/scala/tools/nsc/ast/Trees.scala
index 296d55fec5..b8c59da95c 100644
--- a/src/compiler/scala/tools/nsc/ast/Trees.scala
+++ b/src/compiler/scala/tools/nsc/ast/Trees.scala
@@ -82,7 +82,7 @@ trait Trees extends scala.reflect.internal.Trees { self: Global =>
    *    body
    *  }
    */
-  def Template(parents: List[Tree], self: ValDef, constrMods: Modifiers, vparamss: List[List[ValDef]], argss: List[List[Tree]], body: List[Tree], superPos: Position): Template = {
+  def Template(parents: List[Tree], self: ValDef, constrMods: Modifiers, vparamss: List[List[ValDef]], body: List[Tree], superPos: Position): Template = {
     /* Add constructor to template */
 
     // create parameters for <init> as synthetic trees.
@@ -117,9 +117,16 @@ trait Trees extends scala.reflect.internal.Trees { self: Global =>
         if (vparamss1.isEmpty || !vparamss1.head.isEmpty && vparamss1.head.head.mods.isImplicit)
           vparamss1 = List() :: vparamss1;
         val superRef: Tree = atPos(superPos)(gen.mkSuperSelect)
-        val superCall = (superRef /: argss) (Apply.apply)
+        val superCall = Apply(superRef, Nil) // we can't know in advance which of the parents will end up as a superclass
+                                             // this requires knowing which of the parents is a type macro and which is not
+                                             // and that's something that cannot be found out before typer
+                                             // (the type macros aren't in the trunk yet, but there is a plan for them to land there soon)
+                                             // this means that we don't know what will be the arguments of the super call
+                                             // therefore here we emit a dummy which gets populated when the template is named and typechecked
         List(
-          atPos(wrappingPos(superPos, lvdefs ::: argss.flatten)) (
+          // TODO: previously this was `wrappingPos(superPos, lvdefs ::: argss.flatten)`
+          // is it going to be a problem that we can no longer include the `argss`?
+          atPos(wrappingPos(superPos, lvdefs)) (
             DefDef(constrMods, nme.CONSTRUCTOR, List(), vparamss1, TypeTree(), Block(lvdefs ::: List(superCall), Literal(Constant())))))
       }
     }
@@ -137,11 +144,10 @@ trait Trees extends scala.reflect.internal.Trees { self: Global =>
    *  @param constrMods the modifiers for the class constructor, i.e. as in `class C private (...)`
    *  @param vparamss   the value parameters -- if they have symbols they
    *                    should be owned by `sym`
-   *  @param argss      the supercall arguments
    *  @param body       the template statements without primary constructor
    *                    and value parameter fields.
    */
-  def ClassDef(sym: Symbol, constrMods: Modifiers, vparamss: List[List[ValDef]], argss: List[List[Tree]], body: List[Tree], superPos: Position): ClassDef = {
+  def ClassDef(sym: Symbol, constrMods: Modifiers, vparamss: List[List[ValDef]], body: List[Tree], superPos: Position): ClassDef = {
     // "if they have symbols they should be owned by `sym`"
     assert(
       mforall(vparamss)(p => (p.symbol eq NoSymbol) || (p.symbol.owner == sym)),
@@ -151,7 +157,7 @@ trait Trees extends scala.reflect.internal.Trees { self: Global =>
     ClassDef(sym,
       Template(sym.info.parents map TypeTree,
                if (sym.thisSym == sym || phase.erasedTypes) emptyValDef else ValDef(sym.thisSym),
-               constrMods, vparamss, argss, body, superPos))
+               constrMods, vparamss, body, superPos))
   }
 
  // --- subcomponents --------------------------------------------------