macOS: add a way to hook standard keybinding events

Add macOS specific application handler to deliver macOS specific
events.

Co-authored-by: Mads Marquart <mads@marquart.dk>

examples/window.rs

@@ -22,7 +22,9 @@ use winit::event::{DeviceEvent, DeviceId, Ime, MouseButton, MouseScrollDelta, Wi
 use winit::event_loop::{ActiveEventLoop, EventLoop};
 use winit::keyboard::{Key, ModifiersState};
 #[cfg(macos_platform)]
-use winit::platform::macos::{OptionAsAlt, WindowAttributesExtMacOS, WindowExtMacOS};
+use winit::platform::macos::{
+    ApplicationHandlerExtMacOS, OptionAsAlt, WindowAttributesExtMacOS, WindowExtMacOS,
+};
 #[cfg(any(x11_platform, wayland_platform))]
 use winit::platform::startup_notify::{
     self, EventLoopExtStartupNotify, WindowAttributesExtStartupNotify, WindowExtStartupNotify,
@@ -552,6 +554,23 @@ impl ApplicationHandler for Application {
         // We must drop the context here.
         self.context = None;
     }
+
+    #[cfg(target_os = "macos")]
+    fn macos_handler(&mut self) -> Option<&mut dyn ApplicationHandlerExtMacOS> {
+        Some(self)
+    }
+}
+
+#[cfg(target_os = "macos")]
+impl ApplicationHandlerExtMacOS for Application {
+    fn standard_key_binding(
+        &mut self,
+        _event_loop: &dyn ActiveEventLoop,
+        window_id: WindowId,
+        action: &str,
+    ) {
+        info!(?window_id, ?action, "macOS standard key binding");
+    }
 }
 
 /// State of the window.

src/application.rs

@@ -2,6 +2,8 @@
 
 use crate::event::{DeviceEvent, DeviceId, StartCause, WindowEvent};
 use crate::event_loop::ActiveEventLoop;
+#[cfg(any(docsrs, macos_platform))]
+use crate::platform::macos::ApplicationHandlerExtMacOS;
 use crate::window::WindowId;
 
 /// The handler of the application events.
@@ -343,6 +345,15 @@ pub trait ApplicationHandler {
     fn memory_warning(&mut self, event_loop: &dyn ActiveEventLoop) {
         let _ = event_loop;
     }
+
+    /// The macOS-specific handler.
+    ///
+    /// The return value from this should not change at runtime.
+    #[cfg(any(docsrs, macos_platform))]
+    #[inline(always)]
+    fn macos_handler(&mut self) -> Option<&mut dyn ApplicationHandlerExtMacOS> {
+        None
+    }
 }
 
 #[deny(clippy::missing_trait_methods)]
@@ -411,6 +422,12 @@ impl<A: ?Sized + ApplicationHandler> ApplicationHandler for &mut A {
     fn memory_warning(&mut self, event_loop: &dyn ActiveEventLoop) {
         (**self).memory_warning(event_loop);
     }
+
+    #[cfg(any(docsrs, macos_platform))]
+    #[inline]
+    fn macos_handler(&mut self) -> Option<&mut dyn ApplicationHandlerExtMacOS> {
+        (**self).macos_handler()
+    }
 }
 
 #[deny(clippy::missing_trait_methods)]
@@ -479,4 +496,10 @@ impl<A: ?Sized + ApplicationHandler> ApplicationHandler for Box<A> {
     fn memory_warning(&mut self, event_loop: &dyn ActiveEventLoop) {
         (**self).memory_warning(event_loop);
     }
+
+    #[cfg(any(docsrs, macos_platform))]
+    #[inline]
+    fn macos_handler(&mut self) -> Option<&mut dyn ApplicationHandlerExtMacOS> {
+        (**self).macos_handler()
+    }
 }

src/changelog/unreleased.md

@@ -60,6 +60,8 @@ changelog entry.
   and `Serialize` on many types.
 - Add `MonitorHandle::current_video_mode()`.
 - Add basic iOS IME support. The soft keyboard can now be shown using `Window::set_ime_allowed`.
+- Add `ApplicationHandlerExtMacOS` trait, and a `macos_handler` method to `ApplicationHandler` which returns a `dyn ApplicationHandlerExtMacOS` which allows for macOS specific extensions to winit.
+- Add a `standard_key_binding` method to the `ApplicationHandlerExtMacOS` trait. This allows handling of standard keybindings such as "go to end of line" on macOS.
 - On macOS, add `WindowExtMacOS::set_borderless_game` and `WindowAttributesExtMacOS::with_borderless_game`
   to fully disable the menu bar and dock in Borderless Fullscreen as commonly done in games.
 - Add `WindowId::into_raw()` and `from_raw()`.

src/platform/macos.rs

@@ -75,9 +75,10 @@ use std::os::raw::c_void;
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
+use crate::application::ApplicationHandler;
 use crate::event_loop::{ActiveEventLoop, EventLoopBuilder};
 use crate::monitor::MonitorHandle;
-use crate::window::{Window, WindowAttributes};
+use crate::window::{Window, WindowAttributes, WindowId};
 
 /// Additional methods on [`Window`] that are specific to MacOS.
 pub trait WindowExtMacOS {
@@ -548,3 +549,52 @@ pub enum OptionAsAlt {
     #[default]
     None,
 }
+
+/// Additional events on [`ApplicationHandler`] that are specific to macOS.
+///
+/// This can be registered with [`ApplicationHandler::macos_handler`].
+pub trait ApplicationHandlerExtMacOS: ApplicationHandler {
+    /// The system interpreted a keypress as a standard key binding command.
+    ///
+    /// Examples include inserting tabs and newlines, or moving the insertion point, see
+    /// [`NSStandardKeyBindingResponding`] for the full list of key bindings. They are often text
+    /// editing related.
+    ///
+    /// This corresponds to the [`doCommandBySelector:`] method on `NSTextInputClient`.
+    ///
+    /// The `action` parameter contains the string representation of the selector. Examples include
+    /// `"insertBacktab:"`, `"indent:"` and `"noop:"`.
+    ///
+    /// # Example
+    ///
+    /// ```ignore
+    /// impl ApplicationHandlerExtMacOS for App {
+    ///     fn standard_key_binding(
+    ///         &mut self,
+    ///         event_loop: &dyn ActiveEventLoop,
+    ///         window_id: WindowId,
+    ///         action: &str,
+    ///     ) {
+    ///         match action {
+    ///             "moveBackward:" => self.cursor.position -= 1,
+    ///             "moveForward:" => self.cursor.position += 1,
+    ///             _ => {} // Ignore other actions
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`NSStandardKeyBindingResponding`]: https://developer.apple.com/documentation/appkit/nsstandardkeybindingresponding?language=objc
+    /// [`doCommandBySelector:`]: https://developer.apple.com/documentation/appkit/nstextinputclient/1438256-docommandbyselector?language=objc
+    #[doc(alias = "doCommandBySelector:")]
+    fn standard_key_binding(
+        &mut self,
+        event_loop: &dyn ActiveEventLoop,
+        window_id: WindowId,
+        action: &str,
+    ) {
+        let _ = event_loop;
+        let _ = window_id;
+        let _ = action;
+    }
+}

src/platform_impl/apple/appkit/view.rs

@@ -412,8 +412,9 @@ declare_class!(
         // Basically, we're sent this message whenever a keyboard event that doesn't generate a "human
         // readable" character happens, i.e. newlines, tabs, and Ctrl+C.
         #[method(doCommandBySelector:)]
-        fn do_command_by_selector(&self, _command: Sel) {
+        fn do_command_by_selector(&self, command: Sel) {
             trace_scope!("doCommandBySelector:");
+
             // We shouldn't forward any character from just committed text, since we'll end up sending
             // it twice with some IMEs like Korean one. We'll also always send `Enter` in that case,
             // which is not desired given it was used to confirm IME input.
@@ -428,6 +429,18 @@ declare_class!(
                 // Leave preedit so that we also report the key-up for this key.
                 self.ivars().ime_state.set(ImeState::Ground);
             }
+
+            // Send command action to user if they requested it.
+            let window_id = self.window().id();
+            self.ivars().app_state.maybe_queue_with_handler(move |app, event_loop| {
+                if let Some(handler) = app.macos_handler() {
+                    handler.standard_key_binding(event_loop, window_id, command.name());
+                }
+            });
+
+            // The documentation for `-[NSTextInputClient doCommandBySelector:]` clearly states that
+            // we should not be forwarding this event up the responder chain, so no calling `super`
+            // here either.
         }
     }