Taking a fully-defined result type into account when forming a closure.

Given

     (params) => body

and an expected type

     Ts => R

with R fully defined, we use R as the result type of the closure def into which the function is translated.

Note: It would be nice generalize this further to result types which are not fully defined, yet this would complicate things by entangling typing and desugaring.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index 54ea96eed..7b483adb9 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -420,9 +420,9 @@ object desugar {
    *      def $anonfun(params) = body
    *      Closure($anonfun)
    */
-  def makeClosure(params: List[ValDef], body: Tree) =
+  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree = TypeTree()) =
     Block(
-      DefDef(Modifiers(Synthetic), nme.ANON_FUN, Nil, params :: Nil, TypeTree(), body),
+      DefDef(Modifiers(Synthetic), nme.ANON_FUN, Nil, params :: Nil, tpt, body),
       Closure(Nil, Ident(nme.ANON_FUN), EmptyTree))
 
   /** Expand partial function