deforestation

Signed-off-by: Lucas Pluvinage <[email protected]>

src/dune_load.ml

@@ -26,6 +26,18 @@ module Dune_file = struct
     ; stanzas
     ; kind
     }
+
+  let rec fold_stanzas l ~init ~f =
+    match l with
+    | [] -> init
+    | t :: l -> inner_fold t t.stanzas l ~init ~f
+
+  and inner_fold t inner_list l ~init ~f =
+    match inner_list with
+    | [] -> fold_stanzas l ~init ~f
+    | x :: inner_list ->
+      inner_fold t inner_list l ~init:(f t x init) ~f
+
 end
 
 module Dune_files = struct

src/dune_load.mli

@@ -7,6 +7,12 @@ module Dune_file : sig
     ; stanzas : Dune_file.Stanzas.t
     ; kind    : Dune_lang.File_syntax.t
     }
+
+  val fold_stanzas :
+      t list
+    -> init:'acc
+    -> f:(t -> Stanza.t -> 'acc -> 'acc)
+    -> 'acc
 end
 
 module Dune_files : sig

src/gen_rules.ml

@@ -359,7 +359,7 @@ let gen ~contexts
       | Some pkgs ->
         let visible_libraries =
           stanzas
-          |> List.concat_map ~f:(fun (dir_conf : Dune_load.Dune_file.t) -> dir_conf.stanzas)
+          |> Dune_load.Dune_file.fold_stanzas ~init:[] ~f:(fun _ s acc -> s::acc)
           |> visible_libraries pkgs
         in
         List.map stanzas ~f:(fun (dir_conf : Dune_load.Dune_file.t) ->

src/super_context.ml

@@ -372,13 +372,11 @@ let create
           | _ -> None))
   in
   let internal_implementations =
-    List.concat_map stanzas
-      ~f:(fun { Dune_load.Dune_file.stanzas; _ } ->
-        List.filter_map stanzas ~f:(fun stanza ->
-          match (stanza : Stanza.t) with
-          | Dune_file.External_variant impl -> Some impl
-          | _ -> None)
-      )
+    Dune_load.Dune_file.fold_stanzas stanzas
+      ~init:[]
+      ~f:(fun _ stanza acc -> match stanza with
+        | Dune_file.External_variant impl -> impl::acc
+        | _ -> acc)
   in
   let scopes, public_libs =
     let lib_config = Context.lib_config context in

test/blackbox-tests/test-cases/variants-external-declaration-conflict/run.t

@@ -3,8 +3,8 @@ It is forbidden to declare two external implementations with the same variant.
   $ dune build --root 1/
   Entering directory '1'
   Error: Two implementations of vlibfoo have the same variant "somevariant":
-  - impl1 (dune:6)
   - impl2 (dune:11)
+  - impl1 (dune:6)
   [1]
 
 It is forbidden to declare an external implementation and have a local