add CCIO.File.walk_l

src/core/CCIO.ml

@@ -320,6 +320,14 @@ module File = struct
       )
   *)
 
+  let walk_l d =
+    let l = ref [] in
+    let g = walk d in
+    let rec aux () = match g() with
+      | None -> !l
+      | Some x -> l := x :: !l; aux ()
+    in aux ()
+
   type walk_item = [`File | `Dir] * t
 
   let read_dir ?(recurse=false) d =

src/core/CCIO.mli

@@ -202,6 +202,11 @@ module File : sig
       symlinks, etc.)
       @raise Sys_error in case of error (e.g. permission denied) during iteration *)
 
+  val walk_l : t -> walk_item list
+  (** Same as {!walk} but returns a list (therefore it's eager and might
+      take some time on large directories)
+      @since NEXT_RELEASE *)
+
   val show_walk_item : walk_item -> string
 
   val with_temp :