fix(melange): add loc to Melange_binary.{melc,where} (#6601)

Signed-off-by: Antonio Nuno Monteiro <[email protected]>

src/dune_rules/melange_binary.ml

@@ -1,8 +1,7 @@
 open Import
 
-let melc sctx ~dir =
-  (* TODO loc should come from the mode field in the dune file *)
-  Super_context.resolve_program sctx ~loc:None ~dir ~hint:"opam install melange"
+let melc sctx ~loc ~dir =
+  Super_context.resolve_program sctx ~loc ~dir ~hint:"opam install melange"
     "melc"
 
 let where =
@@ -18,13 +17,13 @@ let where =
   let memo =
     Memo.create "melange-where" ~input:(module Path) ~cutoff:Path.equal impl
   in
-  fun sctx ~dir ->
+  fun sctx ~loc ~dir ->
     let open Memo.O in
     let* env = Super_context.env_node sctx ~dir >>= Env_node.external_env in
     match Env.get env "MELANGELIB" with
     | Some p -> Memo.return (Some (Path.of_string p))
     | None -> (
-      let* melc = melc sctx ~dir in
+      let* melc = melc sctx ~loc ~dir in
       match melc with
       | Error _ -> Memo.return None
       | Ok melc ->

src/dune_rules/melange_binary.mli

@@ -1,5 +1,13 @@
 open Import
 
-val melc : Super_context.t -> dir:Path.Build.t -> Action.Prog.t Memo.t
+val melc :
+     Super_context.t
+  -> loc:Loc.t option
+  -> dir:Path.Build.t
+  -> Action.Prog.t Memo.t
 
-val where : Super_context.t -> dir:Path.Build.t -> Path.t option Memo.t
+val where :
+     Super_context.t
+  -> loc:Loc.t option
+  -> dir:Path.Build.t
+  -> Path.t option Memo.t

src/dune_rules/melange_rules.ml

@@ -57,7 +57,7 @@ let build_js ~loc ~dir ~pkg_name ~mode ~module_system ~dst_dir ~obj_dir ~sctx
     ~lib_deps_js_includes ~js_ext m =
   let cm_kind = Lib_mode.Cm_kind.Melange Cmj in
   let open Memo.O in
-  let* compiler = Melange_binary.melc sctx ~dir in
+  let* compiler = Melange_binary.melc sctx ~loc:(Some loc) ~dir in
   let src = Obj_dir.Module.cm_file_exn obj_dir m ~kind:cm_kind in
   let output = make_js_name ~js_ext ~dst_dir m in
   let obj_dir =
@@ -75,7 +75,7 @@ let build_js ~loc ~dir ~pkg_name ~mode ~module_system ~dst_dir ~obj_dir ~sctx
     "--bs-module-type" :: js_modules_str :: pkg_name_args
   in
   let lib_deps_js_includes = Command.Args.as_any lib_deps_js_includes in
-  Super_context.add_rule sctx ~dir ?loc ~mode
+  Super_context.add_rule sctx ~dir ~loc ~mode
     (Command.run
        ~dir:(Path.build (Super_context.context sctx).build_dir)
        compiler
@@ -140,9 +140,8 @@ let add_rules_for_entries ~sctx ~dir ~expander ~dir_contents ~scope
   let* () =
     Memo.parallel_iter module_list ~f:(fun m ->
         (* Should we check module kind? *)
-        build_js ~dir ~loc:(Some loc) ~pkg_name ~mode
-          ~module_system:mel.module_system ~dst_dir ~obj_dir ~sctx
-          ~lib_deps_js_includes ~js_ext m)
+        build_js ~dir ~loc ~pkg_name ~mode ~module_system:mel.module_system
+          ~dst_dir ~obj_dir ~sctx ~lib_deps_js_includes ~js_ext m)
   in
   let* () =
     match mel.alias with
@@ -181,6 +180,7 @@ let add_rules_for_libraries ~dir ~scope ~target_dir ~sctx ~requires_link ~mode
       in
       let lib = local_of_lib ~loc:mel.loc lib in
       let info = Lib.Local.info lib in
+      let loc = Lib_info.loc info in
       let lib_dir = Lib_info.src_dir info in
       let obj_dir = Lib_info.obj_dir info in
       let dst_dir = lib_output_dir ~target_dir ~lib_dir in
@@ -200,9 +200,8 @@ let add_rules_for_libraries ~dir ~scope ~target_dir ~sctx ~requires_link ~mode
       in
       Memo.parallel_iter source_modules
         ~f:
-          (build_js ~loc:None ~dir ~pkg_name ~mode
-             ~module_system:mel.module_system ~dst_dir ~obj_dir ~sctx
-             ~lib_deps_js_includes ~js_ext))
+          (build_js ~loc ~dir ~pkg_name ~mode ~module_system:mel.module_system
+             ~dst_dir ~obj_dir ~sctx ~lib_deps_js_includes ~js_ext))
 
 let compile_info ~scope (mel : Melange_stanzas.Emit.t) =
   let open Memo.O in

src/dune_rules/merlin.ml

@@ -395,7 +395,7 @@ module Unprocessed = struct
         @@
         match t.config.mode with
         | `Ocaml -> Memo.return (Some stdlib_dir)
-        | `Melange -> Melange_binary.where sctx ~dir
+        | `Melange -> Melange_binary.where sctx ~loc:None ~dir
       in
       let+ flags = flags
       and+ src_dirs, obj_dirs =

src/dune_rules/module_compilation.ml

@@ -96,7 +96,8 @@ let build_cm cctx ~force_write_cmi ~precompiled_cmi ~cm_kind (m : Module.t)
   let* compiler =
     match mode with
     | Melange ->
-      let+ melc = Melange_binary.melc sctx ~dir in
+      let loc = CC.loc cctx in
+      let+ melc = Melange_binary.melc sctx ~loc ~dir in
       Some melc
     | Ocaml mode ->
       Memo.return