From 5649795e6e0d22c9c8071d4cd1ff1781cd5ee1b2 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Sun, 28 Jun 2026 22:38:09 -0700
Subject: [PATCH] fix(melange): stage wrapped root deps for JS emission in the
 sandbox

Signed-off-by: Antonio Nuno Monteiro <anmonteiro@gmail.com>
---
 src/dune_rules/melange/melange_rules.ml       | 19 ++++++++++++++-----
 .../melange/cross-module-opt-deps.t           |  6 ++----
 .../emit-local-transitive-private-module.t    |  1 +
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/dune_rules/melange/melange_rules.ml b/src/dune_rules/melange/melange_rules.ml
index 12552581d5b..4cc918235b8 100644
--- a/src/dune_rules/melange/melange_rules.ml
+++ b/src/dune_rules/melange/melange_rules.ml
@@ -246,6 +246,14 @@ let make_same_lib_emission_deps =
       |> Action_builder.map ~f:melange_cross_module_opt_enabled
     in
     let dep_graph = impl_dep_graph ~sctx ~obj_dir ~modules in
+    let lib_interface_deps =
+      (* The Melange emitter loads the library interface/root artifact when
+         emitting wrapped units such as [Stdlib__Char], even if the source
+         dependency graph does not mention [Stdlib] explicitly. *)
+      Modules.With_vlib.lib_interface modules
+      |> Option.map ~f:(fun m -> deps_of_xopt_closure ~obj_dir [ m ])
+      |> Option.value ~default:Dep.Set.empty
+    in
     fun module_ ->
       let open Action_builder.O in
       xopt_enabled
@@ -264,11 +272,11 @@ let make_same_lib_emission_deps =
             module_
         in
         (* Cross-module optimization follows implementation artifacts, but the
-         initial reachability also comes from the emitted module's interface
-         dependencies. Seed the implementation graph with that interface
-         closure so wrappers such as [Stdlib] stay visible to the emitter. *)
+           initial reachability also comes from the emitted module's interface
+           dependencies. *)
         Dep_graph.top_closed_implementations dep_graph (module_ :: intf_deps)
-        |> Action_builder.map ~f:(deps_of_xopt_closure ~obj_dir)
+        |> Action_builder.map ~f:(fun deps ->
+          Dep.Set.union lib_interface_deps (deps_of_xopt_closure ~obj_dir deps))
       | false ->
         (* Emission reads same-library implementation artifacts recursively.
            Compilation dependencies collapse transitive edges through interfaces
@@ -276,7 +284,8 @@ let make_same_lib_emission_deps =
            emission. Follow the implementation dependency graph directly
            instead. *)
         Dep_graph.top_closed_implementations dep_graph [ module_ ]
-        |> Action_builder.map ~f:(deps_of_closure ~obj_dir ~kind:Cmj)
+        |> Action_builder.map ~f:(fun deps ->
+          Dep.Set.union lib_interface_deps (deps_of_closure ~obj_dir ~kind:Cmj deps))
 ;;
 
 let make_external_lib_emission_deps =
diff --git a/test/blackbox-tests/test-cases/melange/cross-module-opt-deps.t b/test/blackbox-tests/test-cases/melange/cross-module-opt-deps.t
index 8b248694191..91d459f5202 100644
--- a/test/blackbox-tests/test-cases/melange/cross-module-opt-deps.t
+++ b/test/blackbox-tests/test-cases/melange/cross-module-opt-deps.t
@@ -76,10 +76,8 @@ repeat the library's `--mel-cross-module-opt` compile flag.
 
   $ dune describe rules --display=quiet --profile=release dist-default-flags/node_modules/foo/char.js > char-default-rules.sexp
   $ grep -c 'stdlib/.stdlib.objs/melange/stdlib.cmi' char-default-rules.sexp
-  0
-  [1]
+  1
   $ grep -c 'stdlib/.stdlib.objs/melange/stdlib.cmj' char-default-rules.sexp
-  0
-  [1]
+  1
 
   $ dune build dist-default-flags/node_modules/foo/char.js
diff --git a/test/blackbox-tests/test-cases/melange/emit-local-transitive-private-module.t b/test/blackbox-tests/test-cases/melange/emit-local-transitive-private-module.t
index 3cb920e9a53..682d398190b 100644
--- a/test/blackbox-tests/test-cases/melange/emit-local-transitive-private-module.t
+++ b/test/blackbox-tests/test-cases/melange/emit-local-transitive-private-module.t
@@ -15,6 +15,7 @@ transitive implementation closure, even across `.mli` boundaries.
 
   $ dune rules --root . --format=json --deps app/dist/node_modules/repro.foo/foo_map.js |
   > jq_dune -r '.[] | depsFilePaths | select(test("lib/\\.foo\\.objs/melange/.*\\.cmj$")) | sub("^_build/default/"; "")'
+  lib/.foo.objs/melange/foo.cmj
   lib/.foo.objs/melange/foo__Foo_internalAVLtree.cmj
   lib/.foo.objs/melange/foo__Foo_internalMapInt.cmj
   lib/.foo.objs/melange/foo__Foo_map.cmj