Single source of truth for ML export names

The JS export name of an ML binding (identifier conversion, with the ES
default export kept literal) was computed independently at export
emission, qualified-access printing, and the dynamic-import emitter,
agreeing only by convention - with silent undefined-resolution as the
failure mode if any site drifted. Extract
Js_dump_import_export.js_export_name and use it at all four sites.
Byte-identical by construction; the existing regression cases ($$case,
Operator$$plus, default) now pin one function instead of a convention.

Signed-Off-By: Cristiano Calcagno <ccrisccris@gmail.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PCtQiaDijUqA2fujQXvKUw

Author: cristianoc

compiler/core/js_dump.ml

@@ -496,9 +496,7 @@ and vident cxt f (v : J.vident) =
   | Qualified ({id; kind = Ml | Runtime}, Some name) ->
     let cxt = Ext_pp_scope.ident cxt f id in
     P.string f L.dot;
-    P.string f
-      (if name = Js_dump_import_export.default_export then name
-       else Ext_ident.convert name);
+    P.string f (Js_dump_import_export.js_export_name name);
     cxt
   | Qualified ({id; kind = External _}, Some name) ->
     let cxt = Ext_pp_scope.ident cxt f id in

compiler/core/js_dump_import_export.ml

@@ -27,6 +27,14 @@ module L = Js_dump_lit
 
 let default_export = "default"
 
+(* The emitted export name of an ML binding: JS identifier conversion, with
+   the ES default export kept literal. Every site that emits, reads, or
+   reconstructs an ML module's export name must agree with this - the
+   qualified-access printer in [Js_dump] and the dynamic-import emitter in
+   [Lam_compile_primitive] included. *)
+let js_export_name name =
+  if name = default_export then name else Ext_ident.convert name
+
 let es_module = ("__esModule", "true")
 (* Exports printer *)
 
@@ -45,12 +53,12 @@ let exports cxt f (idents : Ident.t list) =
   let outer_cxt, reversed_list =
     Ext_list.fold_left idents (cxt, []) (fun (cxt, acc) id ->
         let id_name = id.name in
-        let s = Ext_ident.convert id_name in
+        let s = js_export_name id_name in
         let str, cxt = Ext_pp_scope.str_of_ident cxt id in
         ( cxt,
           if id_name = default_export then
             (* TODO check how it will affect AMDJS*)
-            es_module :: (default_export, str) :: acc
+            es_module :: (s, str) :: acc
           else (s, str) :: acc ))
   in
   P.at_least_two_lines f;
@@ -77,11 +85,9 @@ let esmodule_export cxt f (idents : Ident.t list) =
     let outer_cxt, reversed_list =
       Ext_list.fold_left idents (cxt, []) (fun (cxt, acc) id ->
           let id_name = id.name in
-          let s = Ext_ident.convert id_name in
+          let s = js_export_name id_name in
           let str, cxt = Ext_pp_scope.str_of_ident cxt id in
-          ( cxt,
-            if id_name = default_export then (default_export, str) :: acc
-            else (s, str) :: acc ))
+          (cxt, (s, str) :: acc))
     in
     P.string f L.export;
     P.space f;

compiler/core/js_dump_import_export.mli

@@ -24,6 +24,12 @@
 
 val default_export : string
 
+val js_export_name : string -> string
+(** The emitted export name of an ML binding: JS identifier conversion,
+    with the ES default export kept literal. The single source of truth
+    for export emission, qualified-access printing, and dynamic-import
+    reconstruction. *)
+
 val exports : Ext_pp_scope.t -> Ext_pp.t -> Ident.t list -> Ext_pp_scope.t
 
 val esmodule_export :

compiler/core/lam_compile_primitive.ml

@@ -131,15 +131,11 @@ let translate output_prefix loc (cxt : Lam_compile_context.t)
       let oid = Lam_module_ident.of_ml ~dynamic_import:true module_ in
       Lam_compile_env.register_ml_module ~dynamic_import:true module_;
       let import = import_of_path (import_path oid) in
-      (* a ReScript module's JS export names go through the same identifier
-         conversion js_dump applies to qualified access and export lists:
-         a binding named [case] is exported as [$$case], and a hoisted
-         [Operator.\"+"] whose cmj metadata stores the raw flattened name
-         [Operator$+] is exported as [Operator$$plus] *)
-      let ml_export_name name =
-        if name = Js_dump_import_export.default_export then name
-        else Ext_ident.convert name
-      in
+      (* the single source of truth for ML export names: a binding named
+         [case] is exported as [$$case], and a hoisted [Operator.\"+"] whose
+         cmj metadata stores the raw flattened name [Operator$+] is
+         exported as [Operator$$plus] *)
+      let ml_export_name = Js_dump_import_export.js_export_name in
       match path with
       | [] -> import
       | [name] -> wrap_then import (ml_export_name name)