X11: Sync key press/release with window focus

[murarth]

• When a window loses focus, key release events are issued for all pressed keys
• When a window gains focus, key press events are issued for all pressed keys
• Adds is_synthetic field to WindowEvent variant KeyboardInput
  to indicate that these events are synthetic.
• Adds is_synthetic: false to WindowEvent::KeyboardInput events issued
  on all other platforms

Addresses #1272 (but doesn't close, as that issue affects other platforms).

• Tested on all platforms changed
• Compilation warnings were addressed
• cargo fmt has been run on this branch
• cargo doc builds successfully
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

[goddessfreya]

So, under i3wm there are some unfortunate focus issues that make this operate in an unexpected manner.

It's hard to spot, but becomes more obvious while testing this PR as it leads to the synthetic key events to get repeated.

For context, the window is on workspace 5 and my terminal on workspace 4. Logo-5 moves your focus to workspace 5, Logo-4 moves it to workspace 4.

More precisely, when Logo-<num> is pressed, ALL windows lose focus, the cursor is moved onto the appropriate workstation and the window that will become focused is highlighted.

The window that will become focused, however, only gains it's focus when the <num> key is released. Releasing the Logo key has no effect.

Here we have the window in focus. We hold Logo then 4. We receive two focus lost events. Upon releasing the 4 we receive a third. This is likely just i3wm being janky and reporting multiple focus lost events to the client that just lost focus- once when it sends it to all clients, and twice for some odd reason to the specific client that lost focus.

NewEvents(WaitCancelled { start: Instant { tv_sec: 2167648, tv_nsec: 411933429 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: ModifiersChanged { modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: false } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167653, tv_nsec: 272226669 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 5, state: Pressed, virtual_keycode: Some(Key4), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }) }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 5, state: Released, virtual_keycode: Some(Key4), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Released, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: Focused(false) }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167654, tv_nsec: 194180513 }, requested_resume: None })
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 5, state: Released, virtual_keycode: Some(Key4), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Released, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: Focused(false) }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167654, tv_nsec: 201562658 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 5, state: Released, virtual_keycode: Some(Key4), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }) }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Released, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: Focused(false) }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: CursorLeft { device_id: DeviceId(X(DeviceId(2))) } }
EventsCleared

However, consider the following: when the window is regaining focus, we receive two focus gained events- one before the <num> key is released and one after. The first focus event actually arrives before the window has gained focus! I tested the behavior out in some other applications: firefox seams to recognize that they have not gained focus, but riot-desktop, keepassxc, file-roller, and xfce4-terminal do not.

NewEvents(WaitCancelled { start: Instant { tv_sec: 2167884, tv_nsec: 50759782 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }) }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167886, tv_nsec: 682480255 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 6, state: Pressed, virtual_keycode: Some(Key5), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }) }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167889, tv_nsec: 258764883 }, requested_resume: None })
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167889, tv_nsec: 267693397 }, requested_resume: None })
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: Focused(true) }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: CursorMoved { device_id: DeviceId(X(DeviceId(2))), position: LogicalPosition { x: -919.3846153846155, y: 488.3076923076923 }, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 6, state: Pressed, virtual_keycode: Some(Key5), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167889, tv_nsec: 270401893 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 6, state: Released, virtual_keycode: Some(Key5), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }) }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: Focused(true) }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: CursorMoved { device_id: DeviceId(X(DeviceId(2))), position: LogicalPosition { x: -919.3846153846155, y: 488.3076923076923 }, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }, is_synthetic: true } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: CursorEntered { device_id: DeviceId(X(DeviceId(2))) } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: CursorMoved { device_id: DeviceId(X(DeviceId(2))), position: LogicalPosition { x: 884.3076923076924, y: 475.3846153846154 }, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: CursorMoved { device_id: DeviceId(X(DeviceId(2))), position: LogicalPosition { x: 884.3076923076924, y: 475.3846153846154 }, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: AxisMotion { device_id: DeviceId(X(DeviceId(2))), axis: 0, value: 2880.0 } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: AxisMotion { device_id: DeviceId(X(DeviceId(2))), axis: 1, value: 539.0 } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 2167894, tv_nsec: 276126253 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 125, state: Released, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } }) }
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: ModifiersChanged { modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } }
WindowEvent { window_id: WindowId(X(WindowId(71303169))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Released, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }, is_synthetic: false } }
EventsCleared

Anyways, as it stands, these synthetic errors are getting duplicated multiple times. I'll leave it up to you to decide if that's okay.

[murarth]

@goddessfreya If there are no further issues with this PR, can I get an explicit approval?