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, 4 insertions, 4 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index cd198818a..60ca45f28 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -218,7 +218,7 @@ object desugar {
 
   /** The expansion of a class definition. See inline comments for what is involved */
   def classDef(cdef: TypeDef)(implicit ctx: Context): Tree = {
-    val TypeDef(name, impl @ Template(constr0, parents, self, body)) = cdef
+    val TypeDef(name, impl @ Template(constr0, parents, self, _)) = cdef
     val mods = cdef.mods
 
     val (constr1, defaultGetters) = defDef(constr0, isPrimaryConstructor = true) match {
@@ -242,7 +242,7 @@ object desugar {
     val constr = cpy.DefDef(constr1)(tparams = constrTparams, vparamss = constrVparamss)
 
     // Add constructor type parameters to auxiliary constructors
-    val normalizedBody = body map {
+    val normalizedBody = impl.body map {
       case ddef: DefDef if ddef.name.isConstructorName =>
         cpy.DefDef(ddef)(tparams = constrTparams)
       case stat =>
@@ -425,10 +425,10 @@ object desugar {
       val modul = ValDef(name, clsRef, New(clsRef, Nil))
         .withMods(mods | ModuleCreationFlags)
         .withPos(mdef.pos)
-      val ValDef(selfName, selfTpt, selfRhs) = tmpl.self
+      val ValDef(selfName, selfTpt, _) = tmpl.self
       val selfMods = tmpl.self.mods
       if (!selfTpt.isEmpty) ctx.error("object definition may not have a self type", tmpl.self.pos)
-      val clsSelf = ValDef(selfName, SingletonTypeTree(Ident(name)), selfRhs)
+      val clsSelf = ValDef(selfName, SingletonTypeTree(Ident(name)), tmpl.self.rhs)
         .withMods(selfMods)
         .withPos(tmpl.self.pos orElse tmpl.pos.startPos)
       val clsTmpl = cpy.Template(tmpl)(self = clsSelf, body = tmpl.body)