Change i32 as exit code to u8

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

src/event_loop.rs

@@ -87,9 +87,11 @@ pub enum ControlFlow {
     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`. The contained number will be used as
-    /// exit code, if the platform supports that (this means _not_ ios, android and wasm32).
-    Exit(i32),
+    /// in the `control_flow` parameter being reset to `Exit`.
+    /// The contained number will be used as exit code, if the platform supports that (this
+    /// _excludes_ ios, android and wasm32), it's an [`u8`] to prevent some weird surprises as
+    /// described in [`std::process::exit`].
+    Exit(u8),
 }
 
 impl Default for ControlFlow {

src/platform/run_return.rs

@@ -22,7 +22,8 @@ pub trait EventLoopExtRunReturn {
     /// Initializes the `winit` event loop.
     ///
     /// Unlike `run`, this function accepts non-`'static` (i.e. non-`move`) closures and returns
-    /// control flow to the caller when `control_flow` is set to `ControlFlow::Exit`.
+    /// control flow to the caller when `control_flow` is set to `ControlFlow::Exit`, where its
+    /// content representing the exit code is the return value.
     ///
     /// # Caveats
     /// Despite its appearance at first glance, this is *not* a perfect replacement for
@@ -33,7 +34,7 @@ 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) -> i32
+    fn run_return<F>(&mut self, event_handler: F) -> u8
     where
         F: FnMut(
             Event<'_, Self::UserEvent>,
@@ -45,7 +46,7 @@ pub trait EventLoopExtRunReturn {
 impl<T> EventLoopExtRunReturn for EventLoop<T> {
     type UserEvent = T;
 
-    fn run_return<F>(&mut self, event_handler: F) -> i32
+    fn run_return<F>(&mut self, event_handler: F) -> u8
     where
         F: FnMut(
             Event<'_, Self::UserEvent>,

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) -> i32
+    pub fn run_return<F>(&mut self, callback: F) -> u8
     where
         F: FnMut(crate::event::Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {

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

@@ -207,10 +207,10 @@ impl<T: 'static> EventLoop<T> {
         F: FnMut(Event<'_, T>, &RootEventLoopWindowTarget<T>, &mut ControlFlow) + 'static,
     {
         let exit_code = self.run_return(callback);
-        process::exit(exit_code);
+        process::exit(i32::from(exit_code));
     }
 
-    pub fn run_return<F>(&mut self, mut callback: F) -> i32
+    pub fn run_return<F>(&mut self, mut callback: F) -> u8
     where
         F: FnMut(Event<'_, T>, &RootEventLoopWindowTarget<T>, &mut ControlFlow),
     {

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) -> i32
+    pub fn run_return<F>(&mut self, mut callback: F) -> u8
     where
         F: FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
@@ -391,7 +391,7 @@ impl<T: 'static> EventLoop<T> {
         F: 'static + FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
         let exit_code = self.run_return(callback);
-        ::std::process::exit(exit_code);
+        ::std::process::exit(i32::from(exit_code));
     }
 
     fn drain_events<F>(&mut self, callback: &mut F, control_flow: &mut ControlFlow)

src/platform_impl/windows/event_loop.rs

@@ -189,10 +189,10 @@ impl<T: 'static> EventLoop<T> {
         F: 'static + FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {
         let exit_code = self.run_return(event_handler);
-        ::std::process::exit(exit_code);
+        ::std::process::exit(i32::from(exit_code));
     }
 
-    pub fn run_return<F>(&mut self, mut event_handler: F) -> i32
+    pub fn run_return<F>(&mut self, mut event_handler: F) -> u8
     where
         F: FnMut(Event<'_, T>, &RootELW<T>, &mut ControlFlow),
     {