SI-6187 Make partial functions re-typable

 - `New(tpe)` doesn't survive a `resetAttrs` / typecheck; use
   a name instead.
 - Abandon the tree attachment that passed the default
   case from `typer` to `patmat`; this tree eluded the
   attribute reset performed in the macro. Instead, add it
   to the match. Apart from making the tree re-typable, it
   also exposes the true code structure to macros, which
   is important if they need to perform other code
   transformations.
 - Install original trees on the declared types of the
   parameters of the `applyOrElse` method to ensure that
   references to them within the method pick up the correct
   type parameter skolems upon retypechecking.
 - Propagate `TypeTree#original` through `copyAttrs`,
   which is called during tree duplication / `TreeCopiers`.
   Without this, the original trees that we installed were
   not visible anymore during `ResetAttrs`.

We are not able to reify partial functions yet -- the
particular sticking point is reification of the parentage
which is only available in the `ClassInfoType`.

1 files changed, 17 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 5522c47cfa..754adcb80d 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -523,7 +523,11 @@ trait Trees extends api.Trees { self: SymbolTable =>
     override private[scala] def copyAttrs(tree: Tree) = {
       super.copyAttrs(tree)
       tree match {
-        case other: TypeTree => wasEmpty = other.wasEmpty // SI-6648 Critical for correct operation of `resetAttrs`.
+        case other: TypeTree =>
+          // SI-6648 Critical for correct operation of `resetAttrs`.
+          wasEmpty = other.wasEmpty
+          if (other.orig != null)
+            orig = other.orig.duplicate
         case _ =>
       }
       this
@@ -984,6 +988,18 @@ trait Trees extends api.Trees { self: SymbolTable =>
   def DefDef(sym: Symbol, mods: Modifiers, rhs: Tree): DefDef =
     DefDef(sym, mods, mapParamss(sym)(ValDef), rhs)
 
+  /** A DefDef with original trees attached to the TypeTree of each parameter */
+  def DefDef(sym: Symbol, mods: Modifiers, originalParamTpts: Symbol => Tree, rhs: Tree): DefDef = {
+    val paramms = mapParamss(sym){ sym =>
+      val vd = ValDef(sym, EmptyTree)
+      (vd.tpt : @unchecked) match {
+        case tt: TypeTree => tt setOriginal (originalParamTpts(sym) setPos sym.pos.focus)
+      }
+      vd
+    }
+    DefDef(sym, mods, paramms, rhs)
+  }
+
   def DefDef(sym: Symbol, rhs: Tree): DefDef =
     DefDef(sym, Modifiers(sym.flags), rhs)