From b6ac955997b11b22480558361a2dc83842cb1b05 Mon Sep 17 00:00:00 2001
From: alanechang <alanechang@janestreet.com>
Date: Mon, 4 Mar 2024 13:08:15 -0500
Subject: [PATCH] Make `Sys.opaque_identity` work on different layouts (#2327)

use layout_poly
---
 ocaml/stdlib/sys.ml.in                                     | 2 +-
 ocaml/stdlib/sys.mli                                       | 2 +-
 ocaml/testsuite/tests/typing-layouts/layout_poly_native.ml | 7 +++++++
 .../tests/typing-layouts/layout_poly_native.reference      | 5 +++++
 4 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/ocaml/stdlib/sys.ml.in b/ocaml/stdlib/sys.ml.in
index 375e347070f..a6c6f618180 100644
--- a/ocaml/stdlib/sys.ml.in
+++ b/ocaml/stdlib/sys.ml.in
@@ -159,7 +159,7 @@ let ocaml_release = {
 
 (* Optimization *)
 
-external opaque_identity : 'a -> 'a = "%opaque"
+external[@layout_poly] opaque_identity : ('a : any). 'a -> 'a = "%opaque"
 
 module Immediate64 = struct
   module type Non_immediate = sig
diff --git a/ocaml/stdlib/sys.mli b/ocaml/stdlib/sys.mli
index cb4c7b619fc..a741360231d 100644
--- a/ocaml/stdlib/sys.mli
+++ b/ocaml/stdlib/sys.mli
@@ -415,7 +415,7 @@ val runtime_warnings_enabled: unit -> bool
 
 (** {1 Optimization} *)
 
-external opaque_identity : 'a -> 'a = "%opaque"
+external[@layout_poly] opaque_identity : ('a : any). 'a -> 'a = "%opaque"
 (** For the purposes of optimization, [opaque_identity] behaves like an
     unknown (and thus possibly side-effecting) function.
 
diff --git a/ocaml/testsuite/tests/typing-layouts/layout_poly_native.ml b/ocaml/testsuite/tests/typing-layouts/layout_poly_native.ml
index 4d4af919cb2..302d1d82061 100644
--- a/ocaml/testsuite/tests/typing-layouts/layout_poly_native.ml
+++ b/ocaml/testsuite/tests/typing-layouts/layout_poly_native.ml
@@ -58,3 +58,10 @@ let () =
   Printf.printf "%s\n" (revapply "abcde" (fun x -> x));
   ()
 
+let () =
+  Printf.printf "%s\n" (N.to_string (Sys.opaque_identity #1n));
+  Printf.printf "%s\n" (I32.to_string (Sys.opaque_identity #2l));
+  Printf.printf "%s\n" (I64.to_string (Sys.opaque_identity #3L));
+  Printf.printf "%s\n" (F.to_string (Sys.opaque_identity #4.));
+  Printf.printf "%s\n" (Sys.opaque_identity "abcde");
+  ()
diff --git a/ocaml/testsuite/tests/typing-layouts/layout_poly_native.reference b/ocaml/testsuite/tests/typing-layouts/layout_poly_native.reference
index 70291b27ca3..e4cf2b6b4b0 100644
--- a/ocaml/testsuite/tests/typing-layouts/layout_poly_native.reference
+++ b/ocaml/testsuite/tests/typing-layouts/layout_poly_native.reference
@@ -23,3 +23,8 @@ abcde
 3
 4.
 abcde
+1
+2
+3
+4.
+abcde