Add arrow keys support to the menu

Alright I had to do it; "it works for me"

src/core/opamConsole.ml

@@ -725,7 +725,7 @@ let short_user_input ~prompt ?default f =
           (* Some keystrokes, e.g. arrows, can return 3 chars *)
           let nr = read stdin buf 0 3 in
           if nr < 1 then raise End_of_file
-          else String.lowercase_ascii (Bytes.sub_string buf 0 nr)
+          else String.uncapitalize_ascii (Bytes.sub_string buf 0 nr)
         with
         | "\n" -> default
         | s -> Some s
@@ -735,7 +735,9 @@ let short_user_input ~prompt ?default f =
       match input with
       | None -> loop ()
       | Some i -> match f i with
-        | Some a -> print_endline i; a
+        | Some a ->
+          if String.length i > 0 && i.[0] <> '\027' then print_endline i;
+          a
         | None -> loop ()
     in
     let attr = tcgetattr stdin in
@@ -775,10 +777,9 @@ let confirm ?(require_unsafe_yes=false) ?(default=true) fmt =
   Printf.ksprintf (fun s ->
       if OpamCoreConfig.(!r.safe_mode) then false else
       let prompt =
-        Printf.sprintf "%s [%s/%s] " s
+        Printf.ksprintf OpamStd.Format.reformat "%s [%s/%s] " s
           (colorise' (`blue :: if default then [`underline] else []) "y")
           (colorise' (`blue :: if default then [] else [`underline]) "n")
-        |> OpamStd.Format.reformat
       in
       if OpamCoreConfig.answer_is `unsafe_yes ||
          not require_unsafe_yes && OpamCoreConfig.answer_is_yes ()
@@ -935,37 +936,63 @@ let menu ?default ?unsafe_yes ?yes ~no ~options fmt =
     List.mapi (fun n (ans, _) -> ans, string_of_int (n+1)) options
   in
   let nums_options = List.map (fun (a, n) -> n, a) options_nums in
-  Printf.ksprintf (fun prompt_msg ->
-      formatted_msg "%s\n" prompt_msg;
-      List.iter (fun (ans, n) ->
-          formatted_msg ~indent:5 "  %s. %s\n"
+  let rec prev_option a0 = function
+    | (a,_)::[] -> a
+    | (a,_)::((a1,_)::_ as r) -> if a1 = a0 then a else prev_option a0 r
+    | [] -> assert false
+  in
+  let rec menu default =
+    let text =
+      OpamStd.List.concat_map "" ~right:"\n" (fun (ans, n) ->
+          Printf.kprintf (OpamStd.Format.reformat ~indent:5) "%s %s. %s\n"
+            (if ans = default then ">" else " ")
             (colorise `blue n)
             (List.assoc ans options))
-        options_nums;
-      let default_s =
-        OpamStd.Option.map (fun a -> (List.assoc a options_nums)) default
-      in
-      let prompt =
-        Printf.sprintf "\n> [%s] "
-          (OpamStd.List.concat_map "/" (fun (n, a) ->
-               colorise'
-                 (`blue :: if Some a = default then [`underline] else [])
-                 n)
-              nums_options)
-      in
-      let select a =
-        msg "%s" (List.assoc a options_nums); a
+        options_nums
+    in
+    let prompt =
+      Printf.sprintf "[%s] "
+        (OpamStd.List.concat_map "/" (fun (n, a) ->
+             colorise'
+               (`blue :: if a = default then [`underline] else [])
+               n)
+            nums_options)
+    in
+    let nlines = List.length Re.(all (compile (char '\n')) text) in
+    msg "%s" text;
+    let select a =
+      msg "%s" (List.assoc a options_nums); a
+    in
+    let default_s = List.assoc default options_nums in
+    if OpamCoreConfig.(!r.safe_mode) then no else
+    match OpamCoreConfig.answer(), unsafe_yes, yes with
+    | `unsafe_yes, Some a, _ -> print_string prompt; select a
+    | #OpamStd.Config.yes_answer, _, Some a -> print_string prompt; select a
+    | `all_no, _, _ -> print_string prompt; select no
+    | _, _, _ ->
+      let default_ref = ref default in
+      let change_selection =
+        fun opt ->
+          carriage_delete ();
+          Printf.printf "\027[%dA" nlines; (* restore cursor pos *)
+          default_ref := opt;
+          raise Exit
       in
-      if OpamCoreConfig.(!r.safe_mode) then no else
-      match OpamCoreConfig.answer(), unsafe_yes, yes with
-      | `unsafe_yes, Some a, _ -> print_string prompt; select a
-      | #OpamStd.Config.yes_answer, _, Some a -> print_string prompt; select a
-      | `all_no, _, _ -> print_string prompt; select no
-      | _, _, _ ->
-        short_user_input ~prompt ?default:default_s @@ function
+      try
+        short_user_input ~prompt ~default:default_s @@ function
         | "" -> None
         | "\027" -> Some (select no) (* echap *)
+        | "\027[A" -> (* up *)
+          change_selection (prev_option default options)
+        | "\027[B" -> (* down *)
+          change_selection (prev_option default (List.rev options))
         | i -> OpamStd.List.assoc_opt i nums_options
+      with Exit -> menu !default_ref
+  in
+  Printf.ksprintf (fun prompt_msg ->
+      formatted_msg "%s\n" prompt_msg;
+      let default = OpamStd.Option.default (fst (List.hd options)) default in
+      menu default
     ) fmt
 
 (* This allows OpamStd.Config.env to display warning messages *)