Add with_grab() and downcasting to KeyboardHandle

Same deal, lets the compositor inspect the grab should it need it.

src/input/keyboard/mod.rs

@@ -2,6 +2,7 @@
 
 use crate::backend::input::KeyState;
 use crate::utils::{IsAlive, Serial, SERIAL_COUNTER};
+use downcast_rs::{impl_downcast, Downcast};
 use std::collections::HashSet;
 #[cfg(feature = "wayland_frontend")]
 use std::sync::RwLock;
@@ -590,7 +591,7 @@ impl<D: SeatHandler + 'static> Clone for GrabStartData<D> {
 /// When your grab ends (either as you requested it or if it was forcefully cancelled by the server),
 /// the struct implementing this trait will be dropped. As such you should put clean-up logic in the destructor,
 /// rather than trying to guess when the grab will end.
-pub trait KeyboardGrab<D: SeatHandler> {
+pub trait KeyboardGrab<D: SeatHandler>: Downcast {
     /// An input was reported.
     ///
     /// `modifiers` are only passed when their state actually changes. The modifier must be
@@ -623,6 +624,8 @@ pub trait KeyboardGrab<D: SeatHandler> {
     fn unset(&mut self, data: &mut D);
 }
 
+impl_downcast!(KeyboardGrab<D> where D: SeatHandler);
+
 /// An handle to a keyboard handler
 ///
 /// It can be cloned and all clones manipulate the same internal state.
@@ -918,6 +921,16 @@ impl<D: SeatHandler + 'static> KeyboardHandle<D> {
         }
     }
 
+    /// Calls `f` with the active grab, if any.
+    pub fn with_grab<T>(&self, f: impl FnOnce(Serial, &dyn KeyboardGrab<D>) -> T) -> Option<T> {
+        let guard = self.arc.internal.lock().unwrap();
+        if let GrabStatus::Active(s, g) = &guard.grab {
+            Some(f(*s, &**g))
+        } else {
+            None
+        }
+    }
+
     /// Handle a keystroke
     ///
     /// All keystrokes from the input backend should be fed _in order_ to this method of the

src/wayland/input_method/mod.rs

@@ -81,7 +81,7 @@ use crate::{
 };
 
 pub use input_method_handle::{InputMethodHandle, InputMethodUserData};
-pub use input_method_keyboard_grab::InputMethodKeyboardUserData;
+pub use input_method_keyboard_grab::{InputMethodKeyboardGrab, InputMethodKeyboardUserData};
 pub use input_method_popup_surface::InputMethodPopupSurfaceUserData;
 
 use super::text_input::TextInputHandle;