Alternative scheme to handle branching

The new scheme alignes If, Match, Try to the scheme used in SeqLiteral.
This favors unboxed over boxed types. It is also simpler than the scheme
in the previous commit.

Author: odersky

src/dotty/tools/dotc/transform/Erasure.scala

@@ -252,28 +252,6 @@ object Erasure extends TypeTestsCasts{
       if (tree.typeOpt.isRef(defn.UnitClass)) tree.withType(tree.typeOpt)
       else super.typedLiteral(tree)
 
-    override def typedIf(tree: untpd.If, pt: Type)(implicit ctx: Context): If = {
-      val tree1 = super.typedIf(tree, pt)
-      if (pt.isValueType) tree1
-      else cpy.If(tree1)(thenp = adapt(tree1.thenp, tree1.tpe), elsep = adapt(tree1.elsep, tree1.tpe))
-    }
-    
-    override def typedMatch(tree: untpd.Match, pt: Type)(implicit ctx: Context): Match = {
-      val tree1 = super.typedMatch(tree, pt).asInstanceOf[Match]
-      if (pt.isValueType) tree1
-      else cpy.Match(tree1)(tree1.selector, tree1.cases.map(adaptCase(_, tree1.tpe)))
-    }
-    
-    override def typedTry(tree: untpd.Try, pt: Type)(implicit ctx: Context): Try = {
-      val tree1 = super.typedTry(tree, pt)
-      if (pt.isValueType) tree1
-      else cpy.Try(tree1)(expr = adapt(tree1.expr, tree1.tpe), cases = tree1.cases.map(adaptCase(_, tree1.tpe)))
-    }
-
-    private def adaptCase(cdef: CaseDef, pt: Type)(implicit ctx: Context): CaseDef = 
-      cpy.CaseDef(cdef)(body = adapt(cdef.body, pt))
-      
-
     /** Type check select nodes, applying the following rewritings exhaustively
      *  on selections `e.m`, where `OT` is the type of the owner of `m` and `ET`
      *  is the erased type of the selection's original qualifier expression.
@@ -409,9 +387,24 @@ object Erasure extends TypeTestsCasts{
       }
     }
 
+    // The following four methods take as the proto-type the erasure of the pre-existing type,
+    // if the original proto-type is not a value type. 
+    // This makes all branches be adapted to the correct type.
     override def typedSeqLiteral(tree: untpd.SeqLiteral, pt: Type)(implicit ctx: Context) =
       super.typedSeqLiteral(tree, erasure(tree.typeOpt))
-        // proto type of typed seq literal is original type; this makes elements be adapted to correct type.
+        // proto type of typed seq literal is original type; 
+
+    override def typedIf(tree: untpd.If, pt: Type)(implicit ctx: Context) =
+      super.typedIf(tree, adaptProto(tree, pt))
+   
+    override def typedMatch(tree: untpd.Match, pt: Type)(implicit ctx: Context) =
+      super.typedMatch(tree, adaptProto(tree, pt))
+    
+    override def typedTry(tree: untpd.Try, pt: Type)(implicit ctx: Context) = 
+      super.typedTry(tree, adaptProto(tree, pt))
+
+    private def adaptProto(tree: untpd.Tree, pt: Type)(implicit ctx: Context) = 
+      if (pt.isValueType) pt else erasure(tree.typeOpt)
 
     override def typedValDef(vdef: untpd.ValDef, sym: Symbol)(implicit ctx: Context): ValDef =
       super.typedValDef(untpd.cpy.ValDef(vdef)(