Stop exporting $$default

Changes.md

@@ -54,6 +54,9 @@ Unreleased
   ([#686](https://github.com/melange-re/melange/pull/686)).
 - [melange]: generate correct code for types with the `option` shape
   ([#700](https://github.com/melange-re/melange/pull/700)).
+- [melange]: stop exporting `$$default` in the generated JavaScript when using
+  ES6 default exports `let default = ..`
+  ([#708](https://github.com/melange-re/melange/pull/708)).
 
 1.0.0 2023-05-31
 ---------------

jscomp/core/js_dump.ml

@@ -523,7 +523,9 @@ and vident cxt (v : J.vident) =
   | Qualified ({ id; kind = Ml | Runtime }, Some name) ->
       let cxt = ident cxt id in
       string cxt L.dot;
-      string cxt (Ext_ident.convert name);
+      string cxt
+        (if name = Js_dump_import_export.default_export then name
+         else Ext_ident.convert name);
       cxt
   | Qualified ({ id; kind = External _ }, Some name) ->
       let cxt = ident cxt id in

jscomp/core/js_dump_import_export.ml

@@ -50,7 +50,7 @@ let exports cxt f (idents : Ident.t list) =
         ( cxt,
           if id_name = default_export then
             (* TODO check how it will affect AMDJS*)
-            esModule :: (default_export, str) :: (s, str) :: acc
+            esModule :: (default_export, str) :: acc
           else (s, str) :: acc ))
       (cxt, []) idents
   in
@@ -79,7 +79,7 @@ let es6_export cxt f (idents : Ident.t list) =
         let str, cxt = Ext_pp_scope.str_of_ident cxt id in
         ( cxt,
           if id_name = default_export then
-            (default_export, str) :: (s, str) :: acc
+            (default_export, str) :: acc
           else (s, str) :: acc ))
       (cxt, []) idents
   in

jscomp/core/js_dump_import_export.mli

@@ -22,6 +22,8 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
+val default_export : string
+
 val exports : Ext_pp_scope.t -> Ext_pp.t -> Ident.t list -> Ext_pp_scope.t
 val es6_export : Ext_pp_scope.t -> Ext_pp.t -> Ident.t list -> Ext_pp_scope.t
 

jscomp/test/dist-es6/jscomp/test/es6_tests/es6_export.mjs

@@ -4,7 +4,6 @@
 var $$default = 3;
 
 export {
-  $$default ,
   $$default as default,
 }
 /* No side effect */

jscomp/test/dist-es6/jscomp/test/es6_tests/es6_import.mjs

@@ -2,7 +2,7 @@
 
 import * as Es6_export from "./es6_export.mjs";
 
-console.log(Es6_export.$$default);
+console.log(Es6_export.default);
 
 export {
 

jscomp/test/es6_tests/es6_export.mjs

@@ -4,7 +4,6 @@
 var $$default = 3;
 
 export {
-  $$default ,
   $$default as default,
 }
 /* No side effect */

jscomp/test/es6_tests/es6_import.mjs

@@ -2,7 +2,7 @@
 
 import * as Es6_export from "./es6_export.mjs";
 
-console.log(Es6_export.$$default);
+console.log(Es6_export.default);
 
 export {
 

test/blackbox-tests/es6-default-exports.t

@@ -0,0 +1,83 @@
+Show that `$$default` exports are not emitted in the resulting JS
+
+  $ . ./setup.sh
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (alias mel)
+  >  (emit_stdlib false)
+  >  (preprocess (pps melange.ppx))
+  >  (module_systems (commonjs js) (es6 mjs)))
+  > EOF
+
+Output a module with a default export
+
+  $ cat > exports_something.ml <<EOF
+  > let default = "world"
+  > EOF
+
+Consume the default export
+
+  $ cat > main.ml <<EOF
+  > let () = Js.log ("Hello, " ^ Exports_something.default)
+  > EOF
+
+  $ dune build @mel
+
+  $ cat ./_build/default/output/exports_something.mjs
+  // Generated by Melange
+
+
+  var $$default = "world";
+
+  export {
+    $$default as default,
+  }
+  /* No side effect */
+
+  $ cat ./_build/default/output/main.mjs
+  // Generated by Melange
+
+  import * as Melange__Exports_something from "./exports_something.mjs";
+
+  console.log("Hello, " + Melange__Exports_something.default);
+
+  export {
+
+  }
+  /*  Not a pure module */
+
+Runs correctly in Node.js
+
+  $ node ./_build/default/output/main.mjs
+  Hello, world
+
+CommonJS:
+
+  $ cat ./_build/default/output/exports_something.js
+  // Generated by Melange
+  'use strict';
+
+
+  var $$default = "world";
+
+  exports.default = $$default;
+  exports.__esModule = true;
+  /* No side effect */
+
+  $ cat ./_build/default/output/main.js
+  // Generated by Melange
+  'use strict';
+
+  var Melange__Exports_something = require("./exports_something.js");
+
+  console.log("Hello, " + Melange__Exports_something.default);
+
+  /*  Not a pure module */
+
+  $ node ./_build/default/output/main.js
+  Hello, world