Show the progress of the file tree scanning

Signed-off-by: François Bobot <francois.bobot@cea.fr>

CHANGES.md

@@ -1,6 +1,9 @@
 2.0.0 (unreleased)
 ------------------
 
+- Indicate the progress of the initial file tree loading (#2459, fixes #2374,
+  @bobot)
+
 - Build `.cm[ox]` files for executables more eagerly. This speeds up builds at
   the cost of building unnecessary artifacts in some cases. Some of these extra
   artifacts can fail to built, so this is a breaking change. (#2268, @rgrinberg)

src/file_tree.ml

@@ -225,8 +225,13 @@ let readdir path =
 
 let load ?(warn_when_seeing_jbuild_file=true) path ~ancestor_vcs =
   let open Result.O in
+  let nb_path_visited = ref 0 in
   let rec walk path ~dirs_visited ~project:parent_project ~vcs ~(dir_status : Sub_dirs.Status.t)
     : (_, _) Result.t =
+    incr nb_path_visited;
+    if !nb_path_visited mod 100 = 0 then
+      Console.update_status_line
+        (Pp.verbatim (Printf.sprintf "scanned %i directories" !nb_path_visited));
     let+ { dirs; files } = readdir path in
     let project =
       if dir_status = Data_only then
@@ -347,14 +352,17 @@ let load ?(warn_when_seeing_jbuild_file=true) path ~ancestor_vcs =
     in
     Dir.create ~path ~contents ~status:dir_status ~project ~vcs
   in
-  match
+  let walk =
     walk path
       ~dirs_visited:(File.Map.singleton (File.of_source_path path) path)
       ~dir_status:Normal
       ~project:(Lazy.force Dune_project.anonymous)
       ~vcs:ancestor_vcs
-  with
-  | Ok dir -> dir
+  in
+  Console.clear_status_line ();
+  match walk with
+  | Ok dir ->
+    dir
   | Error m ->
     User_error.raise [ Pp.textf "Unable to load source %s.@.Reason:%s@."
       (Path.Source.to_string_maybe_quoted path) (Unix.error_message m) ]