event: Unwrap user event in map_nonuser_event Err()

Currently separating an Event<T> into a user event T and Event<()> is
not ergonomic: when map_nonuser_event returns Err() the caller "knows"
this can only contain UserEvent(T), yet has to write additional
unpacking logic to extract the event, with an unnecessary
unreachable!().

Solve this by returning T directly in the Err case, instead of
Event<'a, T>.

CHANGELOG.md

@@ -5,6 +5,7 @@
 - **Breaking:** On Web, remove the `stdweb` backend.
 - Added `Window::focus_window`to bring the window to the front and set input focus.
 - On Wayland and X11, implement `is_maximized` method on `Window`.
+- **Breaking:** `map_nonuser_event` now returns the unwrapped user event `T` in `Err()`.
 
 # 0.25.0 (2021-05-15)
 

src/event.rs

@@ -143,10 +143,10 @@ impl<T: Clone> Clone for Event<'static, T> {
 }
 
 impl<'a, T> Event<'a, T> {
-    pub fn map_nonuser_event<U>(self) -> Result<Event<'a, U>, Event<'a, T>> {
+    pub fn map_nonuser_event<U>(self) -> Result<Event<'a, U>, T> {
         use self::Event::*;
         match self {
-            UserEvent(_) => Err(self),
+            UserEvent(user_event) => Err(user_event),
             WindowEvent { window_id, event } => Ok(WindowEvent { window_id, event }),
             DeviceEvent { device_id, event } => Ok(DeviceEvent { device_id, event }),
             NewEvents(cause) => Ok(NewEvents(cause)),