ppx: fix unused self

Author: hhugo

CHANGES.md

@@ -12,6 +12,7 @@
 * Compiler: fix purity of comparison functions (again) (#2092)
 * Compiler: fix inlining (#2107)
 * Runtime/wasm: fix Unix.times (#2096)
+* Ppx: disable spurious warning for unused "self" in object litteral (#2128)
 
 # 6.2.0 (2025-07-30) - Lille
 

lib/tests/dune.inc

@@ -59,6 +59,16 @@
  (preprocess
   (pps ppx_js_internal ppx_expect)))
 
+(library
+ ;; lib/tests/test_misc.ml
+ (name test_misc_75)
+ (enabled_if true)
+ (modules test_misc)
+ (libraries js_of_ocaml unix)
+ (inline_tests (modes js wasm))
+ (preprocess
+  (pps ppx_js_internal ppx_expect)))
+
 (library
  ;; lib/tests/test_nodejs_filesystem_errors.ml
  (name test_nodejs_filesystem_errors_75)

lib/tests/test_misc.ml

@@ -0,0 +1,10 @@
+open Js_of_ocaml
+
+(* Make sure we don't emit an unused warning for method not using "self" *)
+
+let x =
+  object%js (self)
+    method foo = self##bar
+
+    method bar = ()
+  end

ppx/ppx_js/lib_internal/ppx_js_internal.ml

@@ -697,6 +697,21 @@ let literal_object self_id (fields : field_desc list) =
   let body = function
     | Val (_, _, _, body) -> body
     | Meth (_, _, _, body, _) ->
+        let body =
+          match self_id.ppat_desc with
+          | Ppat_var id ->
+              (* mark self as used to avoid spurious unused-var-strict warning, see gh#2125 *)
+              Ast_builder.Default.pexp_let
+                ~loc:Location.none
+                Nonrecursive
+                [ Ast_builder.Default.value_binding
+                    ~pat:(Ast_builder.Default.ppat_any ~loc:Location.none)
+                    ~loc:Location.none
+                    ~expr:(Ast_builder.Default.evar id.txt ~loc:Location.none)
+                ]
+                body
+          | _ -> body
+        in
         lift_function_body_constraint
           (Ast_builder.Default.pexp_fun
              ~loc:{ body.pexp_loc with loc_ghost = true }