Menu (owebview.Webview

How to call it

set must run on the UI thread — the thread running Webview.run — and on macOS only once the application is active, which it becomes after Webview.run has started. The reliable place is therefore a Webview.dispatch callback, the same pattern Icon.set_app_icon needs:

  Webview.dispatch w (fun w -> Menu.set w menus);
  Webview.run w

Item callbacks are invoked on the UI thread too, so they may drive the webview directly — Webview.eval, Webview.terminate — with no Webview.dispatch in between. An exception escaping a callback is dropped: there is no OCaml handler on the native stack below it.

What differs between platforms

macOS: the menu bar is application-global, so the Webview.t argument is ignored. Note the platform convention: the first menu is the application menu, and the system draws it with the application's own name whatever title you give it. Put your Quit item there, as in the example above, and give the remaining menus their real names.
Linux (GTK 3): the bar belongs to the window, and installing it re-parents webview's widget under a GtkBox. Calling set again replaces the bar rather than stacking a second one. GTK 4 is not supported — it replaced GtkMenuBar with the GMenu model — and set is a no-op there.
Windows: the bar belongs to the window, and its window procedure is subclassed to receive WM_COMMAND. Accelerators take two routes, because WebView2 runs the page in a separate browser process whose input window never feeds this process's message loop. While the page has the focus, set listens to the controller's AcceleratorKeyPressed event. While the host window has it, it installs a WH_GETMESSAGE hook on the calling thread that runs TranslateAccelerator, which webview's own loop does not call. Two consequences. Both belong to the thread that called set, so call it from the UI thread like everything else here. And a menu shortcut takes precedence over the page: a keystroke it claims is swallowed, so a page listening for Ctrl-O will not also see it. This is also why owebview.desktop needs the WebView2 SDK header to build on Windows, just as owebview does.
Any other backend: a no-op.

type modifier =

| Cmd
(*
The platform's primary modifier: Command on macOS, Control on Linux and Windows, where there is no Command key.
*)
| Ctrl
(*
Control, on every platform.
*)
| Alt
(*
Option on macOS, Alt elsewhere.
*)
| Shift

A keyboard modifier.

type item

One entry in a menu: a clickable item, a separator, or a nested submenu.

val item : 
  ?key:char ->
  ?modifiers:modifier list ->
  string ->
  (unit -> unit) ->
  item

item label on_click is a clickable entry that calls on_click () on the UI thread when chosen.

?key and ?modifiers give it a keyboard shortcut: ~key:'o' ~modifiers:[ Cmd ] is Command-O on macOS and Control-O elsewhere. Use a lowercase letter; with no ?key the item has no shortcut, and ?modifiers is then ignored.

val separator : item

A horizontal rule between groups of items.

val submenu : string -> item list -> item

submenu label items nests a menu inside another one.

val set : Webview.t -> (string * item list) list -> unit

set w menus replaces the whole menu bar, menus being the top-level menus in order, each a title and its contents.

Calling it again replaces the previous bar entirely; the callbacks of the old one are released. Passing [] installs an empty bar.