Fix

Author: cknitt

compiler/ml/translcore.ml

@@ -404,13 +404,35 @@ let primitives_table =
 
 let find_primitive prim_name = Hashtbl.find primitives_table prim_name
 
-let warn_on_polymorphic_comparison loc = function
+let is_null_undefined_constant (exp : Typedtree.expression) =
+  match exp.exp_desc with
+  | Texp_ident
+      ( _,
+        _,
+        {
+          val_kind =
+            Val_prim
+              {prim_name = "%null" | "%undefined" | "#null" | "#undefined"; _};
+          _;
+        } ) ->
+    true
+  | _ -> false
+
+let warn_on_polymorphic_comparison loc prim_name args = function
+  (* Preserve the backend's old exemption for == / != against nullish constants,
+     which compile to dedicated null/undefined checks rather than object compare. *)
+  | Pobjcomp (Ceq | Cneq)
+    when prim_name = "%equal_null"
+         || prim_name = "%equal_undefined"
+         || prim_name = "%equal_nullable"
+         || List.exists is_null_undefined_constant args ->
+    ()
   | Pobjcomp _ | Pobjorder | Pobjmin | Pobjmax ->
     Location.prerr_warning loc Warnings.Bs_polymorphic_comparison
   | _ -> ()
 
-let emit_primitive_warnings loc primitive =
-  warn_on_polymorphic_comparison loc primitive;
+let emit_primitive_warnings loc prim_name args primitive =
+  warn_on_polymorphic_comparison loc prim_name args primitive;
   primitive
 
 let specialize_comparison
@@ -455,7 +477,7 @@ let transl_primitive loc p env ty =
   let prim =
     (try specialize_primitive p env ty (* ~has_constant_constructor:false *)
      with Not_found -> Pccall p)
-    |> emit_primitive_warnings loc
+    |> emit_primitive_warnings loc p.prim_name []
   in
   match prim with
   | Ploc kind -> (
@@ -535,7 +557,7 @@ let transl_primitive_application loc prim env ty args =
       if String.length prim_name > 0 && prim_name.[0] = '%' then
         raise (Error (loc, Unknown_builtin_primitive prim_name));
       Pccall prim))
-  |> emit_primitive_warnings loc
+  |> emit_primitive_warnings loc prim_name args
 
 (* To propagate structured constants *)
 

tests/build_tests/super_errors/expected/warning102_nullish_equality.res.expected

@@ -0,0 +1 @@
+

tests/build_tests/super_errors/fixtures/warning102_nullish_equality.res

@@ -0,0 +1,8 @@
+let undefinedEq = undefined == undefined
+let undefinedNeq = undefined != undefined
+
+let nullEq = null == null
+let nullNeq = null != null
+
+let nullableEq = Nullable.undefined == Nullable.make(3)
+let nullableNeq = Nullable.undefined != Nullable.make(3)