(library (extra_objects)): avoid double linking (ocaml#10783)

Signed-off-by: Nicolás Ojeda Bär <n.oje.bar@gmail.com>

doc/changes/10783.md

@@ -0,0 +1,3 @@
+- In a `(library)` stanza with `(extra_objects)` and `(foreign_stubs)`, avoid
+  double linking the extra object files in the final executable.
+  (#10783, @nojb)

src/dune_rules/lib_rules.ml

@@ -289,20 +289,13 @@ let build_stubs lib ~cctx ~dir ~expander ~requires ~dir_contents ~vlib_stubs_o_f
     Foreign_sources.for_lib foreign_sources ~name
   in
   let* o_files =
-    let lib_foreign_o_files =
-      let { Lib_config.ext_obj; _ } = (Compilation_context.ocaml cctx).lib_config in
-      Foreign.Objects.build_paths lib.buildable.extra_objects ~ext_obj ~dir
-    in
-    let+ tbl =
-      Foreign_rules.build_o_files
-        ~sctx
-        ~dir
-        ~expander
-        ~requires
-        ~dir_contents
-        ~foreign_sources
-    in
-    Mode.Map.Multi.add_all tbl Mode.Select.All lib_foreign_o_files
+    Foreign_rules.build_o_files
+      ~sctx
+      ~dir
+      ~expander
+      ~requires
+      ~dir_contents
+      ~foreign_sources
   in
   let all_o_files = Mode.Map.Multi.to_flat_list o_files in
   let* () = Check_rules.add_files sctx ~dir all_o_files in

test/blackbox-tests/test-cases/extra-objects/extra-objects-indirect.t

@@ -0,0 +1,40 @@
+----------------------------------------------------------------------------------
+Build an library which indirectly depends on foreign object files.
+
+----------------------------------------------------------------------------------
+* Building library with indirect dependency on object file
+
+  $ echo "(lang dune 3.5)" > dune-project
+
+  $ mkdir -p lib
+
+  $ cat >lib/dune <<EOF
+  > (library
+  >  (name calc)
+  >  (extra_objects add)
+  >  (foreign_stubs (language c) (names dep)))
+  > EOF
+
+  $ cat >lib/calc.ml <<EOF
+  > external add : int -> int -> int = "add"
+  > EOF
+
+  $ cat >lib/dep.c <<EOF
+  > #include <caml/mlvalues.h>
+  > extern value add(value x, value y);
+  > value dummy() { return add(Val_int(1), Val_int(2)); }
+  > EOF
+
+  $ cat >lib/add.c <<EOF
+  > #include <caml/mlvalues.h>
+  > value add(value x, value y) { return Val_int(Int_val(x) + Int_val(y)); }
+  > EOF
+
+  $ cat >>lib/dune <<EOF
+  > (rule
+  >  (target add.o)
+  >  (deps add.c)
+  >  (action (run %{bin:ocamlc} add.c)))
+  > EOF
+
+  $ dune build