MacOS not sending ReceivedCharacter event

[chrisduerr]

It has been reported to Alacritty that on macOS, specific key combinations do not always emit ReceivedCharacter events on macOS.

The specific example was Ctrl+Q and it appears that while the first press does not emit an event, the second does.

This has been reported to Alacritty in alacritty/alacritty#1359 and here's an excerpt from the relevant event log (full log can be found in the issue):

[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 62, state: Pressed, virtual_keycode: Some(RControl), modifiers: ModifiersState { shift: false, ctrl: true, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 12, state: Pressed, virtual_keycode: Some(Q), modifiers: ModifiersState { shift: false, ctrl: true, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 12, state: Released, virtual_keycode: Some(Q), modifiers: ModifiersState { shift: false, ctrl: true, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 62, state: Released, virtual_keycode: Some(RControl), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 62, state: Pressed, virtual_keycode: Some(RControl), modifiers: ModifiersState { shift: false, ctrl: true, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 12, state: Pressed, virtual_keycode: Some(Q), modifiers: ModifiersState { shift: false, ctrl: true, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: ReceivedCharacter('\u{11}') }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 12, state: Released, virtual_keycode: Some(Q), modifiers: ModifiersState { shift: false, ctrl: true, alt: false, logo: false } } } }
[2019-11-08 10:53] [INFO] glutin event: WindowEvent { window_id: WindowId(Id(140382647460256)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 62, state: Released, virtual_keycode: Some(RControl), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }

[jayache80]

I was just investigating alacritty/alacritty#2788 and I believe it's caused by this bug.

I built winit examples using cargo build --examples and ran target/debug/window and observed its debug output.

Here's the behavior that I observe:

• press and hold "j" and get repeated KeyboardInput and ReceivedCharacter('j') events
• while still holding "j", press and hold "k" and now get repeated KeyboardInput and ReceivedCharacter('k') (and no longer any ReceivedCharacter('j') events
• release "j" (but continue holding "k") and notice the event of releasing "j" KeyboardInput { scancode: 38, state: Released, virtual_keycode: Some(J), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } but not longer getting the ReceivedCharacter('k') events (though still KeyboardInput events corresponding to "k" being held down)

Here's the examples/window output showing that observation with the repeated outputs truncated 3 and some comments interspersed:

### Hold down "j":

WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 38, state: Pressed, virtual_keycode: Some(J), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
WindowEvent { window_id: WindowId(Id(140368075138752)), event: ReceivedCharacter('j') }
EventsCleared
NewEvents(WaitCancelled { start: Instant { t: 24391360193286 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 38, state: Pressed, virtual_keycode: Some(J), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
WindowEvent { window_id: WindowId(Id(140368075138752)), event: ReceivedCharacter('j') }
EventsCleared
NewEvents(WaitCancelled { start: Instant { t: 24391600661713 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 38, state: Pressed, virtual_keycode: Some(J), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
WindowEvent { window_id: WindowId(Id(140368075138752)), event: ReceivedCharacter('j') }
EventsCleared

### While still holding down "j", begin holding down "k":

NewEvents(WaitCancelled { start: Instant { t: 24391872973697 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 40, state: Pressed, virtual_keycode: Some(K), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
WindowEvent { window_id: WindowId(Id(140368075138752)), event: ReceivedCharacter('k') }
EventsCleared
NewEvents(WaitCancelled { start: Instant { t: 24391891868049 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 40, state: Pressed, virtual_keycode: Some(K), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
WindowEvent { window_id: WindowId(Id(140368075138752)), event: ReceivedCharacter('k') }
EventsCleared
NewEvents(WaitCancelled { start: Instant { t: 24392142471924 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 40, state: Pressed, virtual_keycode: Some(K), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
WindowEvent { window_id: WindowId(Id(140368075138752)), event: ReceivedCharacter('k') }
EventsCleared

### Release "j":

NewEvents(WaitCancelled { start: Instant { t: 24392412497351 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 38, state: Released, virtual_keycode: Some(J), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }

### ...but continue holding "k":

WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 40, state: Pressed, virtual_keycode: Some(K), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { t: 24392449916680 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 40, state: Pressed, virtual_keycode: Some(K), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { t: 24392483384856 }, requested_resume: None })
WindowEvent { window_id: WindowId(Id(140368075138752)), event: KeyboardInput { device_id: DeviceId(DeviceId), input: KeyboardInput { scancode: 40, state: Pressed, virtual_keycode: Some(K), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } } } }
EventsCleared

### Notice the lack of accompanying ReceivedCharacter('k') events for the last 3 Some(K) KeyboardInput events

[Osspial]

Re-opening because #1501.

[kchibisov]

There's no such event anymore.