Add example of constructor tag repoted as Unknown.

This happens together with warning:

```
Warning 40: Pdot was selected from type Path.t.
It is not visible in the current scope, and will not
be selected if the type becomes unknown.
```

Author: cristianoc

jscomp/test/variant.js

@@ -1,28 +1,8 @@
 'use strict';
 
 var Block = require("../../lib/js/block.js");
-
-var b = /* B */Block.__(0, [34]);
-
-var c = /* C */Block.__(1, [
-    4,
-    2
-  ]);
-
-var d = /* D */Block.__(2, [/* tuple */[
-      4,
-      2
-    ]]);
-
-console.log("a1", /* A1 */0);
-
-console.log("a2", /* A2 */1);
-
-console.log("b", b);
-
-console.log("c", c);
-
-console.log("d", d);
+var Caml_obj = require("../../lib/js/caml_obj.js");
+var Caml_builtin_exceptions = require("../../lib/js/caml_builtin_exceptions.js");
 
 function foo(param) {
   if (typeof param === "number") {
@@ -74,10 +54,68 @@ function switchNum(param) {
   }
 }
 
+var same = Caml_obj.caml_equal;
+
+var compare = Caml_obj.caml_compare;
+
+var Path = {
+  same: same,
+  compare: compare
+};
+
+function Make(M) {
+  var find = function (x) {
+    return /* () */0;
+  };
+  return {
+          find: find
+        };
+}
+
+function find(x) {
+  return /* () */0;
+}
+
+var M = {
+  find: find
+};
+
+function rollback_path(subst, p) {
+  try {
+    return "try";
+  }
+  catch (exn){
+    if (exn === Caml_builtin_exceptions.not_found) {
+      switch (p.tag | 0) {
+        case /* Unknown */1 :
+            return "Pdot";
+        case /* Unknown */0 :
+        case /* Unknown */2 :
+            return "Pident | Papply";
+        
+      }
+    } else {
+      throw exn;
+    }
+  }
+}
+
 var a1 = /* A1 */0;
 
 var a2 = /* A2 */1;
 
+var b = /* B */Block.__(0, [34]);
+
+var c = /* C */Block.__(1, [
+    4,
+    2
+  ]);
+
+var d = /* D */Block.__(2, [/* tuple */[
+      4,
+      2
+    ]]);
+
 exports.a1 = a1;
 exports.a2 = a2;
 exports.b = b;
@@ -87,4 +125,8 @@ exports.foo = foo;
 exports.fooA1 = fooA1;
 exports.fooC = fooC;
 exports.switchNum = switchNum;
-/*  Not a pure module */
+exports.Path = Path;
+exports.Make = Make;
+exports.M = M;
+exports.rollback_path = rollback_path;
+/* No side effect */

jscomp/test/variant.ml

@@ -11,12 +11,6 @@ let c = C (4,2)
 
 let d = D (4,2)
 
-let () = Js.log2 "a1" a1
-let () = Js.log2 "a2" a2
-let () = Js.log2 "b" b
-let () = Js.log2 "c" c
-let () = Js.log2 "d" d
-
 let foo = function
 | A1 -> 1
 | A2 -> 2
@@ -37,3 +31,27 @@ let switchNum = function
 | 1 -> "1"
 | 2 -> "2"
 | _ -> "_"
+
+module Path = struct
+  type t =
+      Pident of string
+    | Pdot of t * string * int
+    | Papply of t * t
+  let same = (=)
+  let compare = compare
+end
+
+module Make(M : sig type t = Path.t end) = struct
+  type t = M.t
+  let find (x:t) = ()
+end
+
+module M = Make(Path)
+
+let rollback_path subst p =
+  let _ = M.find p in
+  try "try"
+  with Not_found ->
+    match p with
+      Pident _ | Papply _ -> "Pident | Papply"
+    | Pdot _ -> "Pdot"