Make some tree fields lazy

Lazy fields are
 - the rhs field of a ValDef or DefDef
 - the body field of a Template

These can be instantiated with Lazy instances.
The scheme is such that lazy fields are completely
transparent for users of the Trees API.

The only downside is that the parameter used to initialize
a potentially lazy field has a weak type (now it's Any, with
Dotty it would be a union type of the form `T | Lazy[T]`.
Therefore, the parameter cannot be recovered through pattern
matching.

1 files changed, 5 insertions, 6 deletions

diff --git a/src/dotty/tools/dotc/ast/TreeInfo.scala b/src/dotty/tools/dotc/ast/TreeInfo.scala
index 3d633c58d..6ebf29ffa 100644
--- a/src/dotty/tools/dotc/ast/TreeInfo.scala
+++ b/src/dotty/tools/dotc/ast/TreeInfo.scala
@@ -28,8 +28,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
    */
   def isPureInterfaceMember(tree: Tree): Boolean = unsplice(tree) match {
     case EmptyTree | Import(_, _) | TypeDef(_, _) => true
-    case DefDef(_, _, _, _, rhs) => rhs.isEmpty
-    case ValDef(_, _, rhs) => rhs.isEmpty
+    case defn: ValOrDefDef => defn.rhs.isEmpty
     case _ => false
   }
 
@@ -91,7 +90,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
 
   /** If tree is a closure, it's body, otherwise tree itself */
   def closureBody(tree: tpd.Tree): tpd.Tree = tree match {
-    case Block(DefDef(nme.ANON_FUN, _, _, _, rhs) :: Nil, Closure(_, _, _)) => rhs
+    case Block((meth @ DefDef(nme.ANON_FUN, _, _, _, _)) :: Nil, Closure(_, _, _)) => meth.rhs
     case _ => tree
   }
 
@@ -287,8 +286,8 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
        | Import(_, _)
        | DefDef(_, _, _, _, _) =>
       Pure
-    case vdef @ ValDef(_, _, rhs) =>
-      if (vdef.mods is Mutable) Impure else exprPurity(rhs)
+    case vdef @ ValDef(_, _, _) =>
+      if (vdef.mods is Mutable) Impure else exprPurity(vdef.rhs)
     case _ =>
       Impure
   }
@@ -478,7 +477,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
           if (stats exists (definedSym(_) == sym)) stats else Nil
         encl match {
           case Block(stats, _) => verify(stats)
-          case Template(_, _, _, stats) => verify(stats)
+          case encl: Template => verify(encl.body)
           case PackageDef(_, stats) => verify(stats)
           case _ => Nil
         }