Fix OCaml 4.08 compatibility

src/depgraph/dune_describe_graph.ml

@@ -1,5 +1,6 @@
 open Common
 open Dune_describe
+open Std
 
 module Digest_map = Map.Make (Digest)
 
@@ -36,13 +37,11 @@ let g_of_modules parent modules =
   List.fold_left fold_module G.empty modules
 
 let find_library_module_name _library modules: string option =
-  (* TODO: List.find_map isn't on OCaml 4.08 *)
-  List.find_map (fun (m: module_) ->
-      (* TODO: String.ends_with isn't on OCaml 4.08 *)
+  List_compat.find_map (fun (m: module_) ->
       match m.impl with
-      | Some impl when String.ends_with ~suffix:".ml-gen" impl && String.ends_with ~suffix:"__" m.name ->
+      | Some impl when String_compat.ends_with ~suffix:".ml-gen" impl && String_compat.ends_with ~suffix:"__" m.name ->
         Some (String.sub m.name 0 (String.length m.name - 2))
-      | Some impl when String.ends_with ~suffix:".ml-gen" impl ->
+      | Some impl when String_compat.ends_with ~suffix:".ml-gen" impl ->
         Some m.name
       | _ -> None
     ) modules

src/std/list_compat.ml

@@ -0,0 +1,7 @@
+let rec find_map f = function
+  | [] -> None
+  | x :: l -> (
+    match f x with
+    | Some _ as result -> result
+    | None -> find_map f l
+  )

src/std/string_compat.ml

@@ -0,0 +1,11 @@
+open String
+
+let ends_with ~suffix s =
+  let len_s = length s
+  and len_suf = length suffix in
+  let diff = len_s - len_suf in
+  let rec aux i =
+    if i = len_suf then true
+    else if unsafe_get s (diff + i) <> unsafe_get suffix i then false
+    else aux (i + 1)
+  in diff >= 0 && aux 0