Add exit code to ControlFlow::Exit (#2100)

* Add exit code to control flow and impl on linux

* Fix examples to have an exit code

* Fix doc examples to use an exit code

* Improve documentation wording on the exit code

* Add exit code example

* Add exit code on windows

* Change i32 as exit code to u8

This avoids nasty surprises with negative numbers on some unix-alikes
due to two's complement.

* Fix android usages of ControlFlow::Exit

* Fix ios usages of ControlFlow::Exit

* Fix web usages of ControlFlow::Exit

* Add macos exit code

* Add changelog note

* Document exit code on display server disconnection

* Revert "Change i32 as exit code to u8"

This reverts commit f88fba0253b45de6a2ac0c3cbcf01f50503c9396.

* Change Exit to ExitWithCode and make an Exit const

* Revert "Add exit code example"

This reverts commit fbd3d03de9c2d7516c7a63da489c99f498b710df.

* Revert "Fix doc examples to use an exit code"

This reverts commit daabcdf9ef9e16acad715c094ae442529e39fcbc.

* Revert "Fix examples to have an exit code"

This reverts commit 0df486896b8d106acf65ba83c45cc88d60d228e1.

* Fix unix-alike to use ExitWithCode instead of Exit

* Fix windows to use ExitWithCode rather than Exit

* Silence warning about non-uppercase Exit const

* Refactor exit code handling

* Fix macos Exit usage and recover original semantic

* Fix ios to use ExitWithCode instead of Exit

* Update documentation to reflect ExitWithCode

* Fix web to use ExitWithCode when needed, not Exit

* Fix android to use ExitWithCode, not Exit

* Apply documenation nits

* Apply even more documentation nits

* Move change in CHANGELOG.md under "Unreleased"

* Try to use OS error code as exit code on wayland

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+- **Breaking:** Rename the `Exit` variant of `ControlFlow` to `ExitWithCode`, which holds a value to control the exit code after running. Add an `Exit` constant which aliases to `ExitWithCode(0)` instead to avoid major breakage. This shouldn't affect most existing programs.
+
 # 0.26.1 (2022-01-05)
 
 - Fix linking to the `ColorSync` framework on macOS 10.7, and in newer Rust versions.

src/event_loop.rs

@@ -64,9 +64,9 @@ impl<T> fmt::Debug for EventLoopWindowTarget<T> {
 ///
 /// ## Persistency
 /// Almost every change is persistent between multiple calls to the event loop closure within a
-/// given run loop. The only exception to this is `Exit` which, once set, cannot be unset. Changes
-/// are **not** persistent between multiple calls to `run_return` - issuing a new call will reset
-/// the control flow to `Poll`.
+/// given run loop. The only exception to this is `ExitWithCode` which, once set, cannot be unset.
+/// Changes are **not** persistent between multiple calls to `run_return` - issuing a new call will
+/// reset the control flow to `Poll`.
 ///
 /// [events_cleared]: crate::event::Event::RedrawEventsCleared
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -86,9 +86,29 @@ pub enum ControlFlow {
     /// arrives or the given time is reached.
     WaitUntil(Instant),
     /// Send a `LoopDestroyed` event and stop the event loop. This variant is *sticky* - once set,
-    /// `control_flow` cannot be changed from `Exit`, and any future attempts to do so will result
-    /// in the `control_flow` parameter being reset to `Exit`.
-    Exit,
+    /// `control_flow` cannot be changed from `ExitWithCode`, and any future attempts to do so will
+    /// result in the `control_flow` parameter being reset to `ExitWithCode`.
+    ///
+    /// The contained number will be used as exit code. The [`Exit`] constant is a shortcut for this
+    /// with exit code 0.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Android / iOS / WASM**: The supplied exit code is unused.
+    /// - **Unix**: On most Unix-like platforms, only the 8 least significant bits will be used,
+    ///   which can cause surprises with negative exit values (`-42` would end up as `214`). See
+    ///   [`std::process::exit`].
+    ///
+    /// [`Exit`]: ControlFlow::Exit
+    ExitWithCode(i32),
+}
+
+impl ControlFlow {
+    /// Alias for [`ExitWithCode`]`(0)`.
+    ///
+    /// [`ExitWithCode`]: ControlFlow::ExitWithCode
+    #[allow(non_upper_case_globals)]
+    pub const Exit: Self = Self::ExitWithCode(0);
 }
 
 impl Default for ControlFlow {
@@ -145,6 +165,11 @@ impl<T> EventLoop<T> {
     ///
     /// Any values not passed to this function will *not* be dropped.
     ///
+    /// ## Platform-specific
+    ///
+    /// - **X11 / Wayland**: The program terminates with exit code 1 if the display server
+    ///   disconnects.
+    ///
     /// [`ControlFlow`]: crate::event_loop::ControlFlow
     #[inline]
     pub fn run<F>(self, event_handler: F) -> !

src/lib.rs

@@ -31,8 +31,8 @@
 //! You can retrieve events by calling [`EventLoop::run`][event_loop_run]. This function will
 //! dispatch events for every [`Window`] that was created with that particular [`EventLoop`], and
 //! will run until the `control_flow` argument given to the closure is set to
-//! [`ControlFlow`]`::`[`Exit`], at which point [`Event`]`::`[`LoopDestroyed`] is emitted and the
-//! entire program terminates.
+//! [`ControlFlow`]`::`[`ExitWithCode`] (which [`ControlFlow`]`::`[`Exit`] aliases to), at which
+//! point [`Event`]`::`[`LoopDestroyed`] is emitted and the entire program terminates.
 //!
 //! Winit no longer uses a `EventLoop::poll_events() -> impl Iterator<Event>`-based event loop
 //! model, since that can't be implemented properly on some platforms (e.g web, iOS) and works poorly on
@@ -114,6 +114,7 @@
 //! [event_loop_run]: event_loop::EventLoop::run
 //! [`ControlFlow`]: event_loop::ControlFlow
 //! [`Exit`]: event_loop::ControlFlow::Exit
+//! [`ExitWithCode`]: event_loop::ControlFlow::ExitWithCode
 //! [`Window`]: window::Window
 //! [`WindowId`]: window::WindowId
 //! [`WindowBuilder`]: window::WindowBuilder

src/platform/run_return.rs

@@ -33,7 +33,12 @@ pub trait EventLoopExtRunReturn {
     /// underlying OS APIs, which cannot be hidden by `winit` without severe stability repercussions.
     ///
     /// You are strongly encouraged to use `run`, unless the use of this is absolutely necessary.
-    fn run_return<F>(&mut self, event_handler: F)
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Unix-alikes** (**X11** or **Wayland**): This function returns `1` upon disconnection from
+    ///   the display server.
+    fn run_return<F>(&mut self, event_handler: F) -> i32
     where
         F: FnMut(
             Event<'_, Self::UserEvent>,
@@ -45,7 +50,7 @@ pub trait EventLoopExtRunReturn {
 impl<T> EventLoopExtRunReturn for EventLoop<T> {
     type UserEvent = T;
 
-    fn run_return<F>(&mut self, event_handler: F)
+    fn run_return<F>(&mut self, event_handler: F) -> i32
     where
         F: FnMut(
             Event<'_, Self::UserEvent>,

src/platform_impl/android/mod.rs

@@ -73,10 +73,10 @@ pub struct EventLoop<T: 'static> {
 
 macro_rules! call_event_handler {
     ( $event_handler:expr, $window_target:expr, $cf:expr, $event:expr ) => {{
-        if $cf != ControlFlow::Exit {
-            $event_handler($event, $window_target, &mut $cf);
+        if let ControlFlow::ExitWithCode(code) = $cf {
+            $event_handler($event, $window_target, &mut ControlFlow::ExitWithCode(code));
         } else {
-            $event_handler($event, $window_target, &mut ControlFlow::Exit);
+            $event_handler($event, $window_target, &mut $cf);
         }
     }};
 }
@@ -103,11 +103,11 @@ impl<T: 'static> EventLoop<T> {
         F: 'static
             + FnMut(event::Event<'_, T>, &event_loop::EventLoopWindowTarget<T>, &mut ControlFlow),
     {
-        self.run_return(event_handler);
-        ::std::process::exit(0);
+        let exit_code = self.run_return(event_handler);
+        ::std::process::exit(exit_code);
     }
 
-    pub fn run_return<F>(&mut self, mut event_handler: F)
+    pub fn run_return<F>(&mut self, mut event_handler: F) -> i32
     where
         F: FnMut(event::Event<'_, T>, &event_loop::EventLoopWindowTarget<T>, &mut ControlFlow),
     {
@@ -339,7 +339,7 @@ impl<T: 'static> EventLoop<T> {
             );
 
             match control_flow {
-                ControlFlow::Exit => {
+                ControlFlow::ExitWithCode(code) => {
                     self.first_event = poll(
                         self.looper
                             .poll_once_timeout(Duration::from_millis(0))
@@ -349,7 +349,7 @@ impl<T: 'static> EventLoop<T> {
                         start: Instant::now(),
                         requested_resume: None,
                     };
-                    break 'event_loop;
+                    break 'event_loop code;
                 }
                 ControlFlow::Poll => {
                     self.first_event = poll(

src/platform_impl/ios/app_state.rs

@@ -296,7 +296,7 @@ impl AppState {
                 };
                 (waiting_event_handler, event)
             }
-            (ControlFlow::Exit, _) => bug!("unexpected `ControlFlow` `Exit`"),
+            (ControlFlow::ExitWithCode(_), _) => bug!("unexpected `ControlFlow` `Exit`"),
             s => bug!("`EventHandler` unexpectedly woke up {:?}", s),
         };
 
@@ -451,7 +451,7 @@ impl AppState {
                 });
                 self.waker.start()
             }
-            (_, ControlFlow::Exit) => {
+            (_, ControlFlow::ExitWithCode(_)) => {
                 // https://developer.apple.com/library/archive/qa/qa1561/_index.html
                 // it is not possible to quit an iOS app gracefully and programatically
                 warn!("`ControlFlow::Exit` ignored on iOS");

src/platform_impl/linux/mod.rs

@@ -655,7 +655,7 @@ impl<T: 'static> EventLoop<T> {
         x11_or_wayland!(match self; EventLoop(evlp) => evlp.create_proxy(); as EventLoopProxy)
     }
 
-    pub fn run_return<F>(&mut self, callback: F)
+    pub fn run_return<F>(&mut self, callback: F) -> i32
     where
         F: FnMut(crate::event::Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
@@ -741,16 +741,13 @@ fn sticky_exit_callback<T, F>(
 ) where
     F: FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
 {
-    // make ControlFlow::Exit sticky by providing a dummy
-    // control flow reference if it is already Exit.
-    let mut dummy = ControlFlow::Exit;
-    let cf = if *control_flow == ControlFlow::Exit {
-        &mut dummy
+    // make ControlFlow::ExitWithCode sticky by providing a dummy
+    // control flow reference if it is already ExitWithCode.
+    if let ControlFlow::ExitWithCode(code) = *control_flow {
+        callback(evt, target, &mut ControlFlow::ExitWithCode(code))
     } else {
-        control_flow
-    };
-    // user callback
-    callback(evt, target, cf)
+        callback(evt, target, control_flow)
+    }
 }
 
 fn assert_is_main_thread(suggested_method: &str) {

src/platform_impl/linux/wayland/event_loop/mod.rs

@@ -206,11 +206,11 @@ impl<T: 'static> EventLoop<T> {
     where
         F: FnMut(Event<'_, T>, &RootEventLoopWindowTarget<T>, &mut ControlFlow) + 'static,
     {
-        self.run_return(callback);
-        process::exit(0)
+        let exit_code = self.run_return(callback);
+        process::exit(exit_code);
     }
 
-    pub fn run_return<F>(&mut self, mut callback: F)
+    pub fn run_return<F>(&mut self, mut callback: F) -> i32
     where
         F: FnMut(Event<'_, T>, &RootEventLoopWindowTarget<T>, &mut ControlFlow),
     {
@@ -235,7 +235,8 @@ impl<T: 'static> EventLoop<T> {
         // really an option. Instead we inform that the event loop got destroyed. We may
         // communicate an error that something was terminated, but winit doesn't provide us
         // with an API to do that via some event.
-        loop {
+        // Still, we set the exit code to the error's OS error code, or to 1 if not possible.
+        let exit_code = loop {
             // Handle pending user events. We don't need back buffer, since we can't dispatch
             // user events indirectly via callback to the user.
             for user_event in pending_user_events.borrow_mut().drain(..) {
@@ -431,20 +432,19 @@ impl<T: 'static> EventLoop<T> {
                     _ => unreachable!(),
                 };
 
-                if let Ok(dispatched) = queue.dispatch_pending(state, |_, _, _| unimplemented!()) {
-                    dispatched > 0
-                } else {
-                    break;
+                match queue.dispatch_pending(state, |_, _, _| unimplemented!()) {
+                    Ok(dispatched) => dispatched > 0,
+                    Err(error) => break error.raw_os_error().unwrap_or(1),
                 }
             };
 
             match control_flow {
-                ControlFlow::Exit => break,
+                ControlFlow::ExitWithCode(code) => break code,
                 ControlFlow::Poll => {
                     // Non-blocking dispatch.
                     let timeout = Duration::from_millis(0);
-                    if self.loop_dispatch(Some(timeout)).is_err() {
-                        break;
+                    if let Err(error) = self.loop_dispatch(Some(timeout)) {
+                        break error.raw_os_error().unwrap_or(1);
                     }
 
                     callback(
@@ -460,8 +460,8 @@ impl<T: 'static> EventLoop<T> {
                         None
                     };
 
-                    if self.loop_dispatch(timeout).is_err() {
-                        break;
+                    if let Err(error) = self.loop_dispatch(timeout) {
+                        break error.raw_os_error().unwrap_or(1);
                     }
 
                     callback(
@@ -483,8 +483,8 @@ impl<T: 'static> EventLoop<T> {
                         Duration::from_millis(0)
                     };
 
-                    if self.loop_dispatch(Some(duration)).is_err() {
-                        break;
+                    if let Err(error) = self.loop_dispatch(Some(duration)) {
+                        break error.raw_os_error().unwrap_or(1);
                     }
 
                     let now = Instant::now();
@@ -510,9 +510,10 @@ impl<T: 'static> EventLoop<T> {
                     }
                 }
             }
-        }
+        };
 
         callback(Event::LoopDestroyed, &self.window_target, &mut control_flow);
+        exit_code
     }
 
     #[inline]

src/platform_impl/linux/x11/mod.rs

@@ -258,7 +258,7 @@ impl<T: 'static> EventLoop<T> {
         &self.target
     }
 
-    pub fn run_return<F>(&mut self, mut callback: F)
+    pub fn run_return<F>(&mut self, mut callback: F) -> i32
     where
         F: FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
@@ -266,7 +266,7 @@ impl<T: 'static> EventLoop<T> {
         let mut events = Events::with_capacity(8);
         let mut cause = StartCause::Init;
 
-        loop {
+        let exit_code = loop {
             sticky_exit_callback(
                 crate::event::Event::NewEvents(cause),
                 &self.target,
@@ -329,7 +329,7 @@ impl<T: 'static> EventLoop<T> {
             let (deadline, timeout);
 
             match control_flow {
-                ControlFlow::Exit => break,
+                ControlFlow::ExitWithCode(code) => break code,
                 ControlFlow::Poll => {
                     cause = StartCause::Poll;
                     deadline = None;
@@ -376,21 +376,22 @@ impl<T: 'static> EventLoop<T> {
                     requested_resume: deadline,
                 };
             }
-        }
+        };
 
         callback(
             crate::event::Event::LoopDestroyed,
             &self.target,
             &mut control_flow,
         );
+        exit_code
     }
 
     pub fn run<F>(mut self, callback: F) -> !
     where
         F: 'static + FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
-        self.run_return(callback);
-        ::std::process::exit(0);
+        let exit_code = self.run_return(callback);
+        ::std::process::exit(exit_code);
     }
 
     fn drain_events<F>(&mut self, callback: &mut F, control_flow: &mut ControlFlow)

src/platform_impl/macos/app_state.rs

@@ -62,7 +62,6 @@ pub trait EventHandler: Debug {
 
 struct EventLoopHandler<T: 'static> {
     callback: Weak<RefCell<dyn FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow)>>,
-    will_exit: bool,
     window_target: Rc<RootWindowTarget<T>>,
 }
 
@@ -98,25 +97,25 @@ impl<T> Debug for EventLoopHandler<T> {
 impl<T> EventHandler for EventLoopHandler<T> {
     fn handle_nonuser_event(&mut self, event: Event<'_, Never>, control_flow: &mut ControlFlow) {
         self.with_callback(|this, mut callback| {
+            if let ControlFlow::ExitWithCode(code) = *control_flow {
+                let dummy = &mut ControlFlow::ExitWithCode(code);
+                (callback)(event.userify(), &this.window_target, dummy);
+            } else {
                 (callback)(event.userify(), &this.window_target, control_flow);
-            this.will_exit |= *control_flow == ControlFlow::Exit;
-            if this.will_exit {
-                *control_flow = ControlFlow::Exit;
             }
         });
     }
 
     fn handle_user_events(&mut self, control_flow: &mut ControlFlow) {
         self.with_callback(|this, mut callback| {
-            let mut will_exit = this.will_exit;
             for event in this.window_target.p.receiver.try_iter() {
+                if let ControlFlow::ExitWithCode(code) = *control_flow {
+                    let dummy = &mut ControlFlow::ExitWithCode(code);
+                    (callback)(Event::UserEvent(event), &this.window_target, dummy);
+                } else {
                     (callback)(Event::UserEvent(event), &this.window_target, control_flow);
-                will_exit |= *control_flow == ControlFlow::Exit;
-                if will_exit {
-                    *control_flow = ControlFlow::Exit;
                 }
             }
-            this.will_exit = will_exit;
         });
     }
 }
@@ -160,7 +159,10 @@ impl Handler {
     }
 
     fn should_exit(&self) -> bool {
-        *self.control_flow.lock().unwrap() == ControlFlow::Exit
+        matches!(
+            *self.control_flow.lock().unwrap(),
+            ControlFlow::ExitWithCode(_)
+        )
     }
 
     fn get_control_flow_and_update_prev(&self) -> ControlFlow {
@@ -268,16 +270,20 @@ impl AppState {
     ) {
         *HANDLER.callback.lock().unwrap() = Some(Box::new(EventLoopHandler {
             callback,
-            will_exit: false,
             window_target,
         }));
     }
 
-    pub fn exit() {
+    pub fn exit() -> i32 {
         HANDLER.set_in_callback(true);
         HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::LoopDestroyed));
         HANDLER.set_in_callback(false);
         HANDLER.callback.lock().unwrap().take();
+        if let ControlFlow::ExitWithCode(code) = HANDLER.get_old_and_new_control_flow().1 {
+            code
+        } else {
+            0
+        }
     }
 
     pub fn launched(app_delegate: &Object) {
@@ -332,7 +338,7 @@ impl AppState {
                     }
                 }
             }
-            ControlFlow::Exit => StartCause::Poll, //panic!("unexpected `ControlFlow::Exit`"),
+            ControlFlow::ExitWithCode(_) => StartCause::Poll, //panic!("unexpected `ControlFlow::Exit`"),
         };
         HANDLER.set_in_callback(true);
         HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::NewEvents(cause)));
@@ -435,7 +441,7 @@ impl AppState {
         }
         HANDLER.update_start_time();
         match HANDLER.get_old_and_new_control_flow() {
-            (ControlFlow::Exit, _) | (_, ControlFlow::Exit) => (),
+            (ControlFlow::ExitWithCode(_), _) | (_, ControlFlow::ExitWithCode(_)) => (),
             (old, new) if old == new => (),
             (_, ControlFlow::Wait) => HANDLER.waker().stop(),
             (_, ControlFlow::WaitUntil(instant)) => HANDLER.waker().start_at(instant),

src/platform_impl/macos/event_loop.rs

@@ -155,11 +155,11 @@ impl<T> EventLoop<T> {
     where
         F: 'static + FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow),
     {
-        self.run_return(callback);
-        process::exit(0);
+        let exit_code = self.run_return(callback);
+        process::exit(exit_code);
     }
 
-    pub fn run_return<F>(&mut self, callback: F)
+    pub fn run_return<F>(&mut self, callback: F) -> i32
     where
         F: FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow),
     {
@@ -176,7 +176,7 @@ impl<T> EventLoop<T> {
 
         self._callback = Some(Rc::clone(&callback));
 
-        autoreleasepool(|| unsafe {
+        let exit_code = autoreleasepool(|| unsafe {
             let app = NSApp();
             assert_ne!(app, nil);
 
@@ -192,9 +192,11 @@ impl<T> EventLoop<T> {
                 drop(self._callback.take());
                 resume_unwind(panic);
             }
-            AppState::exit();
+            AppState::exit()
         });
         drop(self._callback.take());
+
+        exit_code
     }
 
     pub fn create_proxy(&self) -> Proxy<T> {

src/platform_impl/web/event_loop/runner.rs

@@ -84,7 +84,7 @@ impl<T: 'static> Runner<T> {
     }
 
     fn handle_single_event(&mut self, event: Event<'_, T>, control: &mut root::ControlFlow) {
-        let is_closed = *control == root::ControlFlow::Exit;
+        let is_closed = matches!(*control, root::ControlFlow::ExitWithCode(_));
 
         (self.event_handler)(event, control);
 
@@ -409,7 +409,7 @@ impl<T: 'static> Shared<T> {
             RunnerEnum::Destroyed => return,
         }
 
-        let is_closed = *control == root::ControlFlow::Exit;
+        let is_closed = matches!(*control, root::ControlFlow::ExitWithCode(_));
 
         // Don't take events out of the queue if the loop is closed or the runner doesn't exist
         // If the runner doesn't exist and this method recurses, it will recurse infinitely
@@ -456,7 +456,7 @@ impl<T: 'static> Shared<T> {
                     ),
                 }
             }
-            root::ControlFlow::Exit => State::Exit,
+            root::ControlFlow::ExitWithCode(_) => State::Exit,
         };
 
         match *self.0.runner.borrow_mut() {

src/platform_impl/windows/event_loop.rs

@@ -188,11 +188,11 @@ impl<T: 'static> EventLoop<T> {
     where
         F: 'static + FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
-        self.run_return(event_handler);
-        ::std::process::exit(0);
+        let exit_code = self.run_return(event_handler);
+        ::std::process::exit(exit_code);
     }
 
-    pub fn run_return<F>(&mut self, mut event_handler: F)
+    pub fn run_return<F>(&mut self, mut event_handler: F) -> i32
     where
         F: FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
@@ -209,13 +209,13 @@ impl<T: 'static> EventLoop<T> {
 
         let runner = &self.window_target.p.runner_shared;
 
-        unsafe {
+        let exit_code = unsafe {
             let mut msg = mem::zeroed();
 
             runner.poll();
             'main: loop {
                 if 0 == winuser::GetMessageW(&mut msg, ptr::null_mut(), 0, 0) {
-                    break 'main;
+                    break 'main 0;
                 }
                 winuser::TranslateMessage(&msg);
                 winuser::DispatchMessageW(&msg);
@@ -225,16 +225,20 @@ impl<T: 'static> EventLoop<T> {
                     panic::resume_unwind(payload);
                 }
 
-                if runner.control_flow() == ControlFlow::Exit && !runner.handling_events() {
-                    break 'main;
+                if let ControlFlow::ExitWithCode(code) = runner.control_flow() {
+                    if !runner.handling_events() {
+                        break 'main code;
                     }
                 }
             }
+        };
 
         unsafe {
             runner.loop_destroyed();
         }
+
         runner.reset_runner();
+        exit_code
     }
 
     pub fn create_proxy(&self) -> EventLoopProxy<T> {
@@ -763,7 +767,7 @@ unsafe fn process_control_flow<T: 'static>(runner: &EventLoopRunner<T>) {
                 Box::into_raw(WaitUntilInstantBox::new(until)) as LPARAM,
             );
         }
-        ControlFlow::Exit => (),
+        ControlFlow::ExitWithCode(_) => (),
     }
 }
 

src/platform_impl/windows/event_loop/runner.rs

@@ -241,10 +241,10 @@ impl<T> EventLoopRunner<T> {
             let mut event_handler = self.event_handler.take()
                 .expect("either event handler is re-entrant (likely), or no event handler is registered (very unlikely)");
 
-            if control_flow != ControlFlow::Exit {
-                event_handler(event, &mut control_flow);
+            if let ControlFlow::ExitWithCode(code) = control_flow  {
+                event_handler(event, &mut ControlFlow::ExitWithCode(code));
             } else {
-                event_handler(event, &mut ControlFlow::Exit);
+                event_handler(event, &mut control_flow);
             }
 
             assert!(self.event_handler.replace(Some(event_handler)).is_none());
@@ -372,10 +372,12 @@ impl<T> EventLoopRunner<T> {
         let start_cause = match (init, self.control_flow()) {
             (true, _) => StartCause::Init,
             (false, ControlFlow::Poll) => StartCause::Poll,
-            (false, ControlFlow::Exit) | (false, ControlFlow::Wait) => StartCause::WaitCancelled {
+            (false, ControlFlow::ExitWithCode(_)) | (false, ControlFlow::Wait) => {
+                StartCause::WaitCancelled {
                     requested_resume: None,
                     start: self.last_events_cleared.get(),
-            },
+                }
+            }
             (false, ControlFlow::WaitUntil(requested_resume)) => {
                 if Instant::now() < requested_resume {
                     StartCause::WaitCancelled {