On X11, replay modifiers consumed by XIM

src/platform_impl/linux/x11/util/mod.rs

@@ -1,6 +1,12 @@
 // Welcome to the util module, where we try to keep you from shooting yourself in the foot.
 // *results may vary
 
+use std::{
+    mem::{self, MaybeUninit},
+    ops::BitAnd,
+    os::raw::*,
+};
+
 mod client_msg;
 mod cursor;
 mod geometry;
@@ -12,13 +18,10 @@ pub(crate) mod memory;
 mod randr;
 mod window_property;
 mod wm;
+mod xmodmap;
 
-pub use self::{cursor::*, geometry::*, hint::*, input::*, window_property::*, wm::*};
-
-use std::{
-    mem::{self, MaybeUninit},
-    ops::BitAnd,
-    os::raw::*,
+pub use self::{
+    cursor::*, geometry::*, hint::*, input::*, window_property::*, wm::*, xmodmap::ModifierKeymap,
 };
 
 use super::{atoms::*, ffi, VoidCookie, X11Error, XConnection, XError};

src/platform_impl/linux/x11/util/xmodmap.rs

@@ -0,0 +1,56 @@
+use std::collections::HashSet;
+use std::slice;
+
+use x11_dl::xlib::{KeyCode as XKeyCode, XModifierKeymap};
+
+// Offsets within XModifierKeymap to each set of keycodes.
+// We are only interested in Shift, Control, Alt, and Logo.
+//
+// There are 8 sets total. The order of keycode sets is:
+//     Shift, Lock, Control, Mod1 (Alt), Mod2, Mod3, Mod4 (Logo), Mod5
+//
+// https://tronche.com/gui/x/xlib/input/XSetModifierMapping.html
+const NUM_MODS: usize = 8;
+
+/// Track which keys are modifiers, so we can properly replay them when they were filtered.
+#[derive(Debug, Default)]
+pub struct ModifierKeymap {
+    // Maps keycodes to modifiers
+    modifers: HashSet<XKeyCode>,
+}
+
+impl ModifierKeymap {
+    pub fn new() -> ModifierKeymap {
+        ModifierKeymap::default()
+    }
+
+    pub fn is_modifier(&self, keycode: XKeyCode) -> bool {
+        self.modifers.contains(&keycode)
+    }
+
+    pub fn reload_from_x_connection(&mut self, xconn: &super::XConnection) {
+        unsafe {
+            let keymap = (xconn.xlib.XGetModifierMapping)(xconn.display);
+
+            if keymap.is_null() {
+                return;
+            }
+
+            self.reset_from_x_keymap(&*keymap);
+
+            (xconn.xlib.XFreeModifiermap)(keymap);
+        }
+    }
+
+    fn reset_from_x_keymap(&mut self, keymap: &XModifierKeymap) {
+        let keys_per_mod = keymap.max_keypermod as usize;
+
+        let keys = unsafe {
+            slice::from_raw_parts(keymap.modifiermap as *const _, keys_per_mod * NUM_MODS)
+        };
+        self.modifers.clear();
+        for key in keys {
+            self.modifers.insert(*key);
+        }
+    }
+}