Memoize: duplicate scala2 behaviour: don't create fields for final vals.

This affect initialisation order and we rely on artifacts of initialisation order in Dotty.

1 files changed, 12 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/transform/Memoize.scala b/src/dotty/tools/dotc/transform/Memoize.scala
index 63466dc46..a2954b4a2 100644
--- a/src/dotty/tools/dotc/transform/Memoize.scala
+++ b/src/dotty/tools/dotc/transform/Memoize.scala
@@ -70,13 +70,23 @@ import Decorators._
     lazy val field = sym.field.orElse(newField).asTerm
     if (sym.is(Accessor, butNot = NoFieldNeeded))
       if (sym.isGetter) {
+        def skipBlocks(t: Tree): Tree = t match {
+          case Block(a, b) if a.forall(isIdempotentExpr) => skipBlocks(b)
+          case _ => t
+        }
+        if (sym.is(Flags.Final) && skipBlocks(tree.rhs).isInstanceOf[Literal])
+          // duplicating scalac behavior: for final vals that have rhs as constant, we do not create a field
+          // and instead return the value. This seemingly minor optimization has huge effect on initialization
+          // order and the values that can be observed during superconstructor call
+          tree
+        else {
           var rhs = tree.rhs.changeOwnerAfter(sym, field, thisTransform)
           if (isWildcardArg(rhs)) rhs = EmptyTree
           val fieldDef = transformFollowing(ValDef(field, rhs))
-          val getterDef = cpy.DefDef(tree)(rhs = transformFollowingDeep(ref(field))(ctx.withOwner(sym), info))
+            val getterDef = cpy.DefDef(tree)(rhs = transformFollowingDeep(ref(field))(ctx.withOwner(sym), info))
           Thicket(fieldDef, getterDef)
         }
-      else if (sym.isSetter) {
+      } else if (sym.isSetter) {
         if (!sym.is(ParamAccessor)) { val Literal(Constant(())) = tree.rhs } // this is intended as an assertion
         val initializer = Assign(ref(field), ref(tree.vparamss.head.head.symbol))
         cpy.DefDef(tree)(rhs = transformFollowingDeep(initializer)(ctx.withOwner(sym), info))