feat(ui): better string input dialog

- optionally allow cancelling (for partition view)
- focus the input field on display
- validate on "enter" keypress

Author: AltGr

src/app/learnocaml_common.ml

@@ -143,16 +143,25 @@ let confirm ~title ?(ok_label=[%i"OK"]) ?(cancel_label=[%i"Cancel"]) contents f
     close_button cancel_label;
   ]
 
-let ask_string ~title ?(ok_label=[%i"OK"]) contents =
+let ask_string ~title ?(ok_label=[%i"OK"]) ?(may_cancel=true) contents =
   let input_field =
     H.input ~a:[
         H.a_input_type `Text;
       ] ()
   in
   let result_t, up = Lwt.wait () in
-  ext_alert ~title (contents @ [input_field]) ~buttons:[
-      box_button ok_label (fun () -> Lwt.wakeup up @@ Manip.value input_field)
-    ];
+  let validate _ =
+    Lwt.wakeup up @@ Manip.value input_field
+  in
+  Manip.Ev.onreturn input_field validate;
+  let buttons =
+    box_button ok_label validate
+    :: (if may_cancel
+        then [close_button [%i"Cancel"]]
+        else [])
+  in
+  ext_alert ~title (contents @ [input_field]) ~buttons;
+  Manip.focus input_field;
   result_t
 
 let default_exn_printer = function
@@ -1157,7 +1166,7 @@ let get_token ?(has_server = true) () =
         Lwt.return
     with
     Not_found ->
-      ask_string ~title:"Token"
+      ask_string ~title:"Token" ~may_cancel:false
         [H.txt [%i"Enter your token"]]
       >>= fun input_tok ->
       let token = Token.parse (input_tok) in

src/app/learnocaml_common.mli

@@ -45,6 +45,7 @@ val confirm :
 val ask_string :
   title: string ->
   ?ok_label: string ->
+  ?may_cancel: bool ->
   [< Html_types.div_content > `Input] Tyxml_js.Html.elt list ->
   string Lwt.t
 

src/app/learnocaml_teacher_tab.ml

@@ -211,7 +211,7 @@ let rec teacher_tab token _select _params () =
             in
             let open_partition_ () =
               Lwt.async (fun () ->
-                ask_string ~title:"Choose a function name"
+                ask_string ~title:"Partitioning of student solutions"
                   [H.txt @@ "Choose a function name to partition codes from "^ id ^": "]
                 >|= fun funname ->
                 let _win =