Keep window::open impure (for now)

examples/multi_window/src/main.rs

@@ -42,12 +42,13 @@ enum Message {
 
 impl Example {
     fn new() -> (Self, Task<Message>) {
+        let (_, open) = window::open(window::Settings::default());
+
         (
             Self {
                 windows: BTreeMap::new(),
             },
-            window::open(window::Settings::default())
-                .map(Message::WindowOpened),
+            open.map(Message::WindowOpened),
         )
     }
 
@@ -76,10 +77,12 @@ impl Example {
                             },
                         );
 
-                        window::open(window::Settings {
+                        let (_, open) = window::open(window::Settings {
                             position,
                             ..window::Settings::default()
-                        })
+                        });
+
+                        open
                     })
                     .map(Message::WindowOpened)
             }

runtime/src/window.rs

@@ -18,7 +18,7 @@ use raw_window_handle::WindowHandle;
 #[allow(missing_debug_implementations)]
 pub enum Action {
     /// Opens a new window with some [`Settings`].
-    Open(Settings, oneshot::Sender<Id>),
+    Open(Id, Settings, oneshot::Sender<Id>),
 
     /// Close the window and exits the application.
     Close(Id),
@@ -249,10 +249,15 @@ pub fn close_requests() -> Subscription<Id> {
 
 /// Opens a new window with the given [`Settings`]; producing the [`Id`]
 /// of the new window on completion.
-pub fn open(settings: Settings) -> Task<Id> {
-    task::oneshot(|channel| {
-        crate::Action::Window(Action::Open(settings, channel))
-    })
+pub fn open(settings: Settings) -> (Id, Task<Id>) {
+    let id = Id::unique();
+
+    (
+        id,
+        task::oneshot(|channel| {
+            crate::Action::Window(Action::Open(id, settings, channel))
+        }),
+    )
 }
 
 /// Closes the window with `id`.

test/src/emulator.rs

@@ -145,8 +145,8 @@ impl<P: Program + 'static> Emulator<P> {
                 dbg!(action);
             }
             Action::Window(action) => match action {
-                window::Action::Open(_settings, sender) => {
-                    self.window = core::window::Id::unique();
+                window::Action::Open(id, _settings, sender) => {
+                    self.window = id;
 
                     let _ = sender.send(self.window);
                 }

winit/src/lib.rs

@@ -109,7 +109,7 @@ where
     let task = if let Some(window_settings) = window_settings {
         let mut task = Some(task);
 
-        let open = runtime::window::open(window_settings);
+        let (_id, open) = runtime::window::open(window_settings);
 
         open.then(move |_| task.take().unwrap_or(Task::none()))
     } else {
@@ -1122,8 +1122,7 @@ fn run_action<'a, P, C>(
             }
         },
         Action::Window(action) => match action {
-            window::Action::Open(settings, channel) => {
-                let id = core::window::Id::unique();
+            window::Action::Open(id, settings, channel) => {
                 let monitor = window_manager.last_monitor();
 
                 control_sender