New test.

test/build.ml

@@ -5,7 +5,6 @@ type foo =
   | B of int
   | C of foo * foo [@build fun x y -> C (x, y)]
 
-and point =
-  { x: int; y: int } [@@build fun x y -> { x; y }]
-
-[@@deriving visitors { variety = "map" }]
+and point = Point.point = private { x: int; y: int }
+  [@@build Point.make]
+  [@@deriving visitors { variety = "map" }]

test/misc.mllib

@@ -7,6 +7,7 @@ mapReduce
 map_from_fold
 monopoly
 opaque
+point
 polyclass
 test00
 test01

test/point.ml

+type point =
+  { x: int; y: int }
+
+let make x y = { x; y }

test/point.mli

+type point = private { x: int; y: int }
+val make: int -> int -> point