Refactoring of typedTyped

Goal: Make implementation easier to understand. Prepare the ground for
special-casing of typetagged patterns.

Author: odersky

src/dotty/tools/dotc/typer/Typer.scala

@@ -399,30 +399,38 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   }
 
   def typedTyped(tree: untpd.Typed, pt: Type)(implicit ctx: Context): Tree = track("typedTyped") {
-    def regularTyped(isWildcard: Boolean) = {
-      val tpt1 =
-        if (untpd.isWildcardStarArg(tree))
-          TypeTree(defn.SeqType.appliedTo(pt :: Nil))
-        else
-          checkSimpleKinded(typedType(tree.tpt))
-      val expr1 =
-        if (isWildcard) tree.expr withType tpt1.tpe
-        else typed(tree.expr, tpt1.tpe.widenSkolem)
-      assignType(cpy.Typed(tree)(expr1, tpt1), tpt1)
-    }
-    tree.expr match {
+    /*  Handles three cases:
+     *  @param  ifPat    how to handle a pattern (_: T)
+     *  @param  ifExpr   how to handle an expression (e: T)
+     *  @param  wildName what name `w` to use in the rewriting of
+     *                   (x: T) to (x @ (w: T)). This is either `_` or `_*`.
+     */
+    def cases(ifPat: => Tree, ifExpr: => Tree, wildName: TermName) = tree.expr match {
       case id: untpd.Ident if (ctx.mode is Mode.Pattern) && isVarPattern(id) =>
-        if (id.name == nme.WILDCARD || id.name == nme.WILDCARD_STAR) regularTyped(isWildcard = true)
+        if (id.name == nme.WILDCARD || id.name == nme.WILDCARD_STAR) ifPat
         else {
           import untpd._
-          val name = if (untpd.isWildcardStarArg(tree)) nme.WILDCARD_STAR else nme.WILDCARD
-          typed(Bind(id.name, Typed(Ident(name), tree.tpt)).withPos(id.pos), pt)
+          typed(Bind(id.name, Typed(Ident(wildName), tree.tpt)).withPos(id.pos), pt)
         }
-      case _ =>
-        if (untpd.isWildcardStarArg(tree))
-          seqToRepeated(typedExpr(tree.expr, defn.SeqType))
-        else
-          regularTyped(isWildcard = false)
+      case _ => ifExpr
+    }
+    def ascription(tpt: Tree, isWildcard: Boolean) = {
+      val expr1 =
+        if (isWildcard) tree.expr.withType(tpt.tpe)
+        else typed(tree.expr, tpt.tpe.widenSkolem)
+      assignType(cpy.Typed(tree)(expr1, tpt), tpt)
+    }
+    if (untpd.isWildcardStarArg(tree))
+      cases(
+        ifPat = ascription(TypeTree(defn.SeqType.appliedTo(pt :: Nil)), isWildcard = true),
+        ifExpr = seqToRepeated(typedExpr(tree.expr, defn.SeqType)),
+        wildName = nme.WILDCARD_STAR)
+    else {
+      def tpt1 = checkSimpleKinded(typedType(tree.tpt))
+      cases(
+        ifPat = ascription(tpt1, isWildcard = true),
+        ifExpr = ascription(tpt1, isWildcard = false),
+        wildName = nme.WILDCARD)
     }
   }