Hide cursor while rendering to avoid flickering

src/down.ml

@@ -618,7 +618,10 @@ module Prompt = struct
     | false -> acc
     in
     let ui = String.concat "" (List.rev acc) in
-    clear_ui p; p.output ui;
+    p.output Tty.cursor_hide;
+    clear_ui p;
+    p.output ui;
+    p.output Tty.cursor_show;
     if active then (p.last_cr <- cr; p.last_max_r <- max_r)
 
   let render_id_complete p prefix candidates =

src/down_std.ml

@@ -439,6 +439,8 @@ module Tty = struct
   let cursor_forward n =
     if n = 0 then "" else String.concat "" ["\x1B["; string_of_int n; "C"]
 
+  let cursor_hide = "\x1B[?25l"
+  let cursor_show = "\x1B[?25h"
   let cursor_origin = "\x1B[H"
   let clear_screen = "\x1B[2J"
 

src/down_std.mli

@@ -294,6 +294,12 @@ module Tty : sig
   val cursor_forward : int -> string
   (** [cursor_forward n] moves cursor by [n] columns. *)
 
+  val cursor_hide : string
+  (** [cursor_hide] hides the cursor. *)
+
+  val cursor_show : string
+  (** [cursor_show] shows the cursor. *)
+
   val cursor_origin : string
   (** [cursor_origin] moves cursor to the top-left origin. *)