On X11, avoid false positive key repeats

Instead of a single `bool` indicating that a key press has occured and
no key has been released since then, we store the scancode of the last
pressed key (if it is a key that repeats when held). This fixes a bug
where pressing a new key while one is already held down will be flagged
as a repeat even though it is obviously not a repeat.

CHANGELOG.md

@@ -8,6 +8,8 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- On X11, fix false positive flagging of key repeats when pressing different keys with no release
+  between presses.
 - Implement `PartialOrd` and `Ord` for `KeyCode` and `NativeKeyCode`.
 
 # 0.29.0-beta.0

src/platform_impl/linux/common/xkb_state.rs

@@ -354,7 +354,6 @@ impl KbdState {
         self.post_init(state, keymap);
     }
 
-    #[cfg(feature = "wayland")]
     pub fn key_repeats(&mut self, keycode: ffi::xkb_keycode_t) -> bool {
         unsafe { (XKBH.xkb_keymap_key_repeats)(self.xkb_keymap, keycode) == 1 }
     }

src/platform_impl/linux/x11/event_processor.rs

@@ -31,8 +31,11 @@ pub(super) struct EventProcessor<T: 'static> {
     pub(super) kb_state: KbdState,
     // Number of touch events currently in progress
     pub(super) num_touch: u32,
-    // Whether we've got a key release for the key press.
-    pub(super) got_key_release: bool,
+    // This is the last pressed key that is repeatable (if it hasn't been
+    // released).
+    //
+    // Used to detect key repeats.
+    pub(super) held_key_press: Option<u32>,
     pub(super) first_touch: Option<u64>,
     // Currently focused window belonging to this process
     pub(super) active_window: Option<ffi::Window>,
@@ -548,13 +551,39 @@ impl<T: 'static> EventProcessor<T> {
                 let device_id = mkdid(util::VIRTUAL_CORE_KEYBOARD);
 
                 let keycode = xkev.keycode as _;
-                let repeat = ty == ffi::KeyPress && !self.got_key_release;
-                // Update state after the repeat setting.
+
+                // Update state to track key repeats and determine whether this key was a repeat.
+                //
+                // Note, when a key is held before focusing on this window the first
+                // (non-synthetic) event will not be flagged as a repeat (also note that the
+                // synthetic press event that is generated before this when the window gains focus
+                // will also not be flagged as a repeat).
+                //
+                // Only keys that can repeat should change the held_key_press state since a
+                // continuously held repeatable key may continue repeating after the press of a
+                // non-repeatable key.
+                let repeat = if self.kb_state.key_repeats(keycode) {
+                    let is_latest_held = self.held_key_press == Some(keycode);
+
+                    if ty == ffi::KeyPress {
+                        self.held_key_press = Some(keycode);
+                        is_latest_held
+                    } else {
+                        // Check that the released key is the latest repeatable key that has been
+                        // pressed, since repeats will continue for the latest key press if a
+                        // different previously pressed key is released.
+                        if is_latest_held {
+                            self.held_key_press = None;
+                        }
+                        false
+                    }
+                } else {
+                    false
+                };
+
                 let state = if ty == ffi::KeyPress {
-                    self.got_key_release = false;
                     ElementState::Pressed
                 } else {
-                    self.got_key_release = true;
                     ElementState::Released
                 };
 
@@ -926,6 +955,9 @@ impl<T: 'static> EventProcessor<T> {
                                 &mut self.kb_state,
                                 &mut callback,
                             );
+                            // Clear this so detecting key repeats is consistently handled when the
+                            // window regains focus.
+                            self.held_key_press = None;
 
                             callback(Event::WindowEvent {
                                 window_id,

src/platform_impl/linux/x11/mod.rs

@@ -289,10 +289,10 @@ impl<T: 'static> EventLoop<T> {
             xkbext,
             kb_state,
             num_touch: 0,
+            held_key_press: None,
             first_touch: None,
             active_window: None,
             is_composing: false,
-            got_key_release: true,
         };
 
         // Register for device hotplug events