api: add ApplicationHandler and matching run APIs

Add a simple `ApplicationHandler` trait since winit is moving towards
trait based API. Add `run_app` group of APIs to accept `&mut impl
ApplicationHandler` deprecating the old `run` APIs.

Part-of: https://github.com/rust-windowing/winit/issues/3432

src/platform/pump_events.rs

@@ -1,22 +1,13 @@
 use std::time::Duration;
 
-use crate::{
-    event::Event,
-    event_loop::{ActiveEventLoop, EventLoop},
-};
-
-/// The return status for `pump_events`
-pub enum PumpStatus {
-    /// Continue running external loop.
-    Continue,
-    /// Exit external loop.
-    Exit(i32),
-}
+use crate::application::ApplicationHandler;
+use crate::event::Event;
+use crate::event_loop::{self, ActiveEventLoop, EventLoop};
 
 /// Additional methods on [`EventLoop`] for pumping events within an external event loop
 pub trait EventLoopExtPumpEvents {
     /// A type provided by the user that can be passed through [`Event::UserEvent`].
-    type UserEvent;
+    type UserEvent: 'static;
 
     /// Pump the `EventLoop` to check for and dispatch pending events.
     ///
@@ -113,6 +104,21 @@ pub trait EventLoopExtPumpEvents {
     ///   If you render outside of Winit you are likely to see window resizing artifacts
     ///   since MacOS expects applications to render synchronously during any `drawRect`
     ///   callback.
+    fn pump_app_events<A: ApplicationHandler<Self::UserEvent>>(
+        &mut self,
+        timeout: Option<Duration>,
+        app: &mut A,
+    ) -> PumpStatus {
+        #[allow(deprecated)]
+        self.pump_events(timeout, |event, event_loop| {
+            event_loop::dispatch_event_for_app(app, event_loop, event)
+        })
+    }
+
+    /// See [`pump_app_events`].
+    ///
+    /// [`pump_app_events`]: Self::pump_app_events
+    #[deprecated = "use EventLoopExtPumpEvents::pump_app_events"]
     fn pump_events<F>(&mut self, timeout: Option<Duration>, event_handler: F) -> PumpStatus
     where
         F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
@@ -128,3 +134,11 @@ impl<T> EventLoopExtPumpEvents for EventLoop<T> {
         self.event_loop.pump_events(timeout, event_handler)
     }
 }
+
+/// The return status for `pump_events`
+pub enum PumpStatus {
+    /// Continue running external loop.
+    Continue,
+    /// Exit external loop.
+    Exit(i32),
+}

src/platform/run_on_demand.rs

@@ -1,8 +1,7 @@
-use crate::{
-    error::EventLoopError,
-    event::Event,
-    event_loop::{ActiveEventLoop, EventLoop},
-};
+use crate::application::ApplicationHandler;
+use crate::error::EventLoopError;
+use crate::event::Event;
+use crate::event_loop::{self, ActiveEventLoop, EventLoop};
 
 #[cfg(doc)]
 use crate::{platform::pump_events::EventLoopExtPumpEvents, window::Window};
@@ -10,12 +9,19 @@ use crate::{platform::pump_events::EventLoopExtPumpEvents, window::Window};
 /// Additional methods on [`EventLoop`] to return control flow to the caller.
 pub trait EventLoopExtRunOnDemand {
     /// A type provided by the user that can be passed through [`Event::UserEvent`].
-    type UserEvent;
+    type UserEvent: 'static;
 
-    /// Runs the event loop in the calling thread and calls the given `event_handler` closure
-    /// to dispatch any window system events.
+    /// See [`run_app_on_demand`].
     ///
-    /// Unlike [`EventLoop::run`], this function accepts non-`'static` (i.e. non-`move`) closures
+    /// [`run_app_on_demand`]: Self::run_app_on_demand
+    #[deprecated = "use EventLoopExtRunOnDemand::run_app_on_demand"]
+    fn run_on_demand<F>(&mut self, event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
+
+    /// Run the application with the event loop on the calling thread.
+    ///
+    /// Unlike [`EventLoop::run_app`], this function accepts non-`'static` (i.e. non-`move`) closures
     /// and it is possible to return control back to the caller without
     /// consuming the `EventLoop` (by using [`exit()`]) and
     /// so the event loop can be re-run after it has exit.
@@ -26,11 +32,10 @@ pub trait EventLoopExtRunOnDemand {
     ///
     /// This API is not designed to run an event loop in bursts that you can exit from and return
     /// to while maintaining the full state of your application. (If you need something like this
-    /// you can look at the [`EventLoopExtPumpEvents::pump_events()`] API)
+    /// you can look at the [`EventLoopExtPumpEvents::pump_app_events()`] API)
     ///
-    /// Each time `run_on_demand` is called the `event_handler` can expect to receive a
-    /// `NewEvents(Init)` and `Resumed` event (even on platforms that have no suspend/resume
-    /// lifecycle) - which can be used to consistently initialize application state.
+    /// Each time `run_app_on_demand` is called the startup sequence of `init`, followed by
+    /// `resume` is being preserved.
     ///
     /// See the [`set_control_flow()`] docs on how to change the event loop's behavior.
     ///
@@ -40,8 +45,8 @@ pub trait EventLoopExtRunOnDemand {
     ///   backend it is possible to use `EventLoopExtWebSys::spawn()`[^1] more than once instead).
     /// - No [`Window`] state can be carried between separate runs of the event loop.
     ///
-    /// You are strongly encouraged to use [`EventLoop::run()`] for portability, unless you specifically need
-    /// the ability to re-run a single event loop more than once
+    /// You are strongly encouraged to use [`EventLoop::run_app()`] for portability, unless you
+    /// specifically need the ability to re-run a single event loop more than once
     ///
     /// # Supported Platforms
     /// - Windows
@@ -64,9 +69,15 @@ pub trait EventLoopExtRunOnDemand {
     ///
     /// [`exit()`]: ActiveEventLoop::exit()
     /// [`set_control_flow()`]: ActiveEventLoop::set_control_flow()
-    fn run_on_demand<F>(&mut self, event_handler: F) -> Result<(), EventLoopError>
-    where
-        F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
+    fn run_app_on_demand<A: ApplicationHandler<Self::UserEvent>>(
+        &mut self,
+        app: &mut A,
+    ) -> Result<(), EventLoopError> {
+        #[allow(deprecated)]
+        self.run_on_demand(|event, event_loop| {
+            event_loop::dispatch_event_for_app(app, event_loop, event)
+        })
+    }
 }
 
 impl<T> EventLoopExtRunOnDemand for EventLoop<T> {

src/platform/web.rs

@@ -53,9 +53,10 @@ use std::time::Duration;
 #[cfg(web_platform)]
 use web_sys::HtmlCanvasElement;
 
+use crate::application::ApplicationHandler;
 use crate::cursor::CustomCursorSource;
 use crate::event::Event;
-use crate::event_loop::{ActiveEventLoop, EventLoop};
+use crate::event_loop::{self, ActiveEventLoop, EventLoop};
 #[cfg(web_platform)]
 use crate::platform_impl::CustomCursorFuture as PlatformCustomCursorFuture;
 use crate::platform_impl::PlatformCustomCursorSource;
@@ -160,18 +161,18 @@ impl WindowAttributesExtWebSys for WindowAttributes {
 /// Additional methods on `EventLoop` that are specific to the web.
 pub trait EventLoopExtWebSys {
     /// A type provided by the user that can be passed through `Event::UserEvent`.
-    type UserEvent;
+    type UserEvent: 'static;
 
     /// Initializes the winit event loop.
     ///
     /// Unlike
     #[cfg_attr(
         all(web_platform, target_feature = "exception-handling"),
-        doc = "`run()`"
+        doc = "`run_app()`"
     )]
     #[cfg_attr(
         not(all(web_platform, target_feature = "exception-handling")),
-        doc = "[`run()`]"
+        doc = "[`run_app()`]"
     )]
     /// [^1], this returns immediately, and doesn't throw an exception in order to
     /// satisfy its [`!`] return type.
@@ -183,9 +184,15 @@ pub trait EventLoopExtWebSys {
     ///
     #[cfg_attr(
         not(all(web_platform, target_feature = "exception-handling")),
-        doc = "[`run()`]: EventLoop::run()"
+        doc = "[`run_app()`]: EventLoop::run_app()"
     )]
-    /// [^1]: `run()` is _not_ available on WASM when the target supports `exception-handling`.
+    /// [^1]: `run_app()` is _not_ available on WASM when the target supports `exception-handling`.
+    fn spawn_app<A: ApplicationHandler<Self::UserEvent> + 'static>(self, app: A);
+
+    /// See [`spawn_app`].
+    ///
+    /// [`spawn_app`]: Self::spawn_app
+    #[deprecated = "use EventLoopExtWebSys::spawn_app"]
     fn spawn<F>(self, event_handler: F)
     where
         F: 'static + FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
@@ -194,6 +201,12 @@ pub trait EventLoopExtWebSys {
 impl<T> EventLoopExtWebSys for EventLoop<T> {
     type UserEvent = T;
 
+    fn spawn_app<A: ApplicationHandler<Self::UserEvent> + 'static>(self, mut app: A) {
+        self.event_loop.spawn(move |event, event_loop| {
+            event_loop::dispatch_event_for_app(&mut app, event_loop, event)
+        });
+    }
+
     fn spawn<F>(self, event_handler: F)
     where
         F: 'static + FnMut(Event<Self::UserEvent>, &ActiveEventLoop),