Terminal not restored properly after exiting alt screen

[hedyhli]

Ideally, a TUI that makes use of an alt screen should restore the screen state and cursor after exiting. This is the expected behaviour of TUI apps that uses an alt screen.

Expected:

prompt $ echo hi
hi
prompt $ ./main.exe  # enters alt screen
prompt $ |           # cursor here after TUI finishes

Actual:
When the TUI exits, the terminal outputs and prompts of the previous one or two commands are gone, including the ./main.exe line that runs the TUI itself.

Demo

open Minttea

type model = { quitting : bool }

let init _ = Command.Enter_alt_screen
let initial_model = { quitting = false }

let update event model =
  match event with
  | Event.KeyDown (Key "q" | Escape) ->
      ({ quitting = true }, Command.Quit)
  | _ -> (model, Command.Noop)

let view model =
  if model.quitting then ""
  else
    "in alt screen"

let () = Minttea.app ~init ~update ~view () |> Minttea.start ~initial_model

Workaround

open Minttea

type model = { quitting : bool; in_alt : bool }

let ref = Riot.Ref.make ()
let init _ = Command.Set_timer (ref, 0.1)
let initial_model = { quitting = false; in_alt = false }

let update event model =
  match event with
  | Event.KeyDown (Key "q" | Escape) ->
      ({ model with quitting = true }, Command.Quit)
  (* Entering alt screen after initialization fixes the issue. *)
  | Event.Timer _ref -> ({model with in_alt = true}, Command.Enter_alt_screen)
  | _ -> (model, Command.Noop)

let view model =
  if not model.in_alt then " "  (* empty string does not work *)
  else if model.quitting then ""
  else
    "in alt screen"

let () = Minttea.app ~init ~update ~view () |> Minttea.start ~initial_model

Unfortunately, I didn't find a way to remove the newline produced before entering alt screen, and the extra newline after exiting.

[hedyhli]

Welp, it looks like it's a duplicate #6

Perhaps it's included in 0.0.3 which isn't yet on opam (#54)?