From 8925ad61b56cd489ca9a4ac41be5ddb223dc3557 Mon Sep 17 00:00:00 2001
From: Antonio Nuno Monteiro <anmonteiro@gmail.com>
Date: Thu, 23 Feb 2023 22:51:46 -0800
Subject: [PATCH] melange: interpret `melc --where` as a list of `:`-separated
 paths

Signed-off-by: Antonio Nuno Monteiro <anmonteiro@gmail.com>
---
 src/dune_rules/melange/melange_binary.ml  | 29 ++++++++++++++---------
 src/dune_rules/melange/melange_binary.mli |  5 +---
 src/dune_rules/merlin/merlin.ml           | 17 +++++++++----
 3 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/src/dune_rules/melange/melange_binary.ml b/src/dune_rules/melange/melange_binary.ml
index ad9d352363c8..5e88d4b0d2f1 100644
--- a/src/dune_rules/melange/melange_binary.ml
+++ b/src/dune_rules/melange/melange_binary.ml
@@ -13,20 +13,27 @@ let where =
       @@ Process.run_capture_line ~display:Quiet Process.Strict bin
            [ "--where" ]
     in
-    Path.of_string where
+    where
   in
   let memo =
-    Memo.create "melange-where" ~input:(module Path) ~cutoff:Path.equal impl
+    Memo.create "melange-where" ~input:(module Path) ~cutoff:String.equal impl
   in
   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 ~loc ~dir in
-      match melc with
-      | Error _ -> Memo.return None
-      | Ok melc ->
-        let+ res = Memo.exec memo melc in
-        Some res)
+    let+ melange_dirs =
+      match Env.get env "MELANGELIB" with
+      | Some p -> Memo.return (Some p)
+      | None -> (
+        let* melc = melc sctx ~loc ~dir in
+        match melc with
+        | Error _ -> Memo.return None
+        | Ok melc ->
+          let+ res = Memo.exec memo melc in
+          Some res)
+    in
+    Option.map
+      ~f:(fun dirs ->
+        String.split ~on:Bin.path_sep dirs |> List.map ~f:Path.of_string)
+      melange_dirs
+    |> Option.value ~default:[]
diff --git a/src/dune_rules/melange/melange_binary.mli b/src/dune_rules/melange/melange_binary.mli
index 0ffd13a73512..17429d73ca0d 100644
--- a/src/dune_rules/melange/melange_binary.mli
+++ b/src/dune_rules/melange/melange_binary.mli
@@ -7,7 +7,4 @@ val melc :
   -> Action.Prog.t Memo.t
 
 val where :
-     Super_context.t
-  -> loc:Loc.t option
-  -> dir:Path.Build.t
-  -> Path.t option Memo.t
+  Super_context.t -> loc:Loc.t option -> dir:Path.Build.t -> Path.t list Memo.t
diff --git a/src/dune_rules/merlin/merlin.ml b/src/dune_rules/merlin/merlin.ml
index e465f43e51a3..bc2b75195baf 100644
--- a/src/dune_rules/merlin/merlin.ml
+++ b/src/dune_rules/merlin/merlin.ml
@@ -466,12 +466,18 @@ module Unprocessed = struct
        } as t) sctx ~dir ~more_src_dirs ~expander =
     let open Action_builder.O in
     let+ config =
-      let* stdlib_dir =
+      let* stdlib_dir, extra_obj_dirs =
         Action_builder.of_memo
         @@
         match t.config.mode with
-        | `Ocaml -> Memo.return (Some stdlib_dir)
-        | `Melange -> Melange_binary.where sctx ~loc:None ~dir
+        | `Ocaml -> Memo.return (Some stdlib_dir, [])
+        | `Melange -> (
+          let open Memo.O in
+          let+ dirs = Melange_binary.where sctx ~loc:None ~dir in
+          match dirs with
+          | [] -> (None, [])
+          | [ stdlib_dir ] -> (Some stdlib_dir, [])
+          | stdlib_dir :: extra_obj_dirs -> (Some stdlib_dir, extra_obj_dirs))
       in
       let* flags = flags
       and* src_dirs, obj_dirs =
@@ -481,7 +487,10 @@ module Unprocessed = struct
               let+ dirs = src_dirs sctx lib in
               (lib, dirs))
           >>| List.fold_left
-                ~init:(Path.set_of_source_paths source_dirs, objs_dirs)
+                ~init:
+                  ( Path.set_of_source_paths source_dirs
+                  , Path.Set.union objs_dirs (Path.Set.of_list extra_obj_dirs)
+                  )
                 ~f:(fun (src_dirs, obj_dirs) (lib, more_src_dirs) ->
                   ( Path.Set.union src_dirs more_src_dirs
                   , let public_cmi_dir =