Add partial fix to anonymous application of FunctionX

This will fail on tree-checks because we're not assigning a type to the
created val.

Author: felixmulder

src/dotty/tools/dotc/typer/Applications.scala

@@ -573,6 +573,12 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
               else
                 new ApplyToUntyped(tree, fun1, funRef, proto, pt)(argCtx(tree))
             convertNewGenericArray(ConstFold(app.result))
+          case mt: MethodType =>
+            val applyVal = untpd.ValDef(ctx.freshName("applyVal").toTermName, untpd.TypeTree(), tree.fun)
+            val valBlock =
+              untpd.Block(applyVal :: Nil, untpd.Apply(untpd.Ident(applyVal.name), tree.args))
+
+            typed(valBlock, pt)
           case _ =>
             handleUnexpectedFunType(tree, fun1)
         }