Remove EventLoopError::AlreadyRunning

This is already prevented by the type-system, and as such it doesn't
make sense to have an error case for this.

CHANGELOG.md

@@ -37,6 +37,7 @@ Unreleased` header.
 - on Windows: add `with_system_backdrop`, `with_border_color`, `with_title_background_color`, `with_title_text_color` and `with_corner_preference`
 - On Windows, Remove `WS_CAPTION`, `WS_BORDER` and `WS_EX_WINDOWEDGE` styles for child windows without decorations.
 - On Windows, fixed a race condition when sending an event through the loop proxy.
+- **Breaking:** Removed `EventLoopError::AlreadyRunning`, which can't happen as it is already prevented by the type system.
 
 # 0.29.10
 

src/error.rs

@@ -35,8 +35,6 @@ pub enum EventLoopError {
     NotSupported(NotSupportedError),
     /// The OS cannot perform the operation.
     Os(OsError),
-    /// The event loop can't be re-run while it's already running
-    AlreadyRunning,
     /// The event loop can't be re-created.
     RecreationAttempt,
     /// Application has exit with an error status.
@@ -105,7 +103,6 @@ impl fmt::Display for NotSupportedError {
 impl fmt::Display for EventLoopError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
         match self {
-            EventLoopError::AlreadyRunning => write!(f, "EventLoop is already running"),
             EventLoopError::RecreationAttempt => write!(f, "EventLoop can't be recreated"),
             EventLoopError::NotSupported(e) => e.fmt(f),
             EventLoopError::Os(e) => e.fmt(f),

src/platform/run_on_demand.rs

@@ -55,7 +55,7 @@ pub trait EventLoopExtRunOnDemand {
     ///   loop that would block the browser and there is nothing that can be
     ///   polled to ask for new events. Events are delivered via callbacks based
     ///   on an event loop that is internal to the browser itself.
-    /// - **iOS:** It's not possible to stop and start an `NSApplication` repeatedly on iOS.
+    /// - **iOS:** It's not possible to stop and start an `UIApplication` repeatedly on iOS.
     ///
     #[cfg_attr(
         not(web_platform),
@@ -87,3 +87,16 @@ impl EventLoopWindowTarget {
         self.p.clear_exit()
     }
 }
+
+/// ```compile_fail
+/// use winit::event_loop::EventLoop;
+/// use winit::platform::run_on_demand::EventLoopExtRunOnDemand;
+///
+/// let mut event_loop = EventLoop::new().unwrap();
+/// event_loop.run_on_demand(|_, _| {
+///     // Attempt to run the event loop re-entrantly; this must fail.
+///     event_loop.run_on_demand(|_, _| {});
+/// });
+/// ```
+#[allow(dead_code)]
+fn test_run_on_demand_cannot_access_event_loop() {}

src/platform_impl/android/mod.rs

@@ -491,10 +491,6 @@ impl<T: 'static> EventLoop<T> {
     where
         F: FnMut(event::Event<T>, &event_loop::EventLoopWindowTarget),
     {
-        if self.loop_running {
-            return Err(EventLoopError::AlreadyRunning);
-        }
-
         loop {
             match self.pump_events(None, &mut event_handler) {
                 PumpStatus::Exit(0) => {

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

@@ -192,10 +192,6 @@ impl<T: 'static> EventLoop<T> {
     where
         F: FnMut(Event<T>, &RootEventLoopWindowTarget),
     {
-        if self.loop_running {
-            return Err(EventLoopError::AlreadyRunning);
-        }
-
         let exit = loop {
             match self.pump_events(None, &mut event_handler) {
                 PumpStatus::Exit(0) => {

src/platform_impl/linux/x11/mod.rs

@@ -402,10 +402,6 @@ impl<T: 'static> EventLoop<T> {
     where
         F: FnMut(Event<T>, &RootELW),
     {
-        if self.loop_running {
-            return Err(EventLoopError::AlreadyRunning);
-        }
-
         let exit = loop {
             match self.pump_events(None, &mut event_handler) {
                 PumpStatus::Exit(0) => {

src/platform_impl/macos/event_loop.rs

@@ -279,10 +279,6 @@ impl<T> EventLoop<T> {
     where
         F: FnMut(Event<T>, &RootWindowTarget),
     {
-        if self.delegate.is_running() {
-            return Err(EventLoopError::AlreadyRunning);
-        }
-
         let callback = map_user_event(callback, self.receiver.clone());
 
         // # Safety

src/platform_impl/windows/event_loop.rs

@@ -94,8 +94,6 @@ use crate::{
 };
 use runner::{EventLoopRunner, EventLoopRunnerShared};
 
-use self::runner::RunnerState;
-
 use super::{window::set_skip_taskbar, SelectedCursor};
 
 /// some backends like macos uses an uninhabited `Never` type,
@@ -246,9 +244,6 @@ impl<T: 'static> EventLoop<T> {
     {
         {
             let runner = &self.window_target.p.runner_shared;
-            if runner.state() != RunnerState::Uninitialized {
-                return Err(EventLoopError::AlreadyRunning);
-            }
 
             let event_loop_windows_ref = &self.window_target;
             let user_event_receiver = &self.user_event_receiver;

src/platform_impl/windows/event_loop/runner.rs

@@ -143,10 +143,6 @@ impl<T> EventLoopRunner<T> {
         }
     }
 
-    pub fn state(&self) -> RunnerState {
-        self.runner_state.get()
-    }
-
     pub fn set_control_flow(&self, control_flow: ControlFlow) {
         self.control_flow.set(control_flow)
     }